Search a list of records: Difference between revisions
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=={{header|Mathematica}}== |
=={{header|Mathematica}}/{{header|Wolfram Language}}== |
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<lang Mathematica> |
<lang Mathematica>data = Dataset[{ |
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data = Dataset[{ |
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<|"name" -> "Lagos", "population" -> 21.|>, |
<|"name" -> "Lagos", "population" -> 21.|>, |
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<|"name" -> "Cairo", "population" -> 15.2|>, |
<|"name" -> "Cairo", "population" -> 15.2|>, |
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<|"name" -> "Casablanca", "population" -> 3.98|> |
<|"name" -> "Casablanca", "population" -> 3.98|> |
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}] |
}] |
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data[Position["Dar Es Salaam"], "name"][1, 1] - 1 |
data[Position["Dar Es Salaam"], "name"][1, 1] - 1 |
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data[Select[#population < 5 &]][1, "name"] |
data[Select[#population < 5 &]][1, "name"] |
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data[Select[StringMatchQ[#name, "A*"] &]][1, "population"]</lang> |
data[Select[StringMatchQ[#name, "A*"] &]][1, "population"]</lang> |
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=={{header|Nim}}== |
=={{header|Nim}}== |
Revision as of 10:02, 14 August 2021
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
You are encouraged to solve this task according to the task description, using any language you may know.
Many programming languages provide convenient ways to look for a known value in a simple list of strings or numbers.
But what if the elements of the list are themselves compound records/objects/data-structures, and the search condition is more complex than a simple equality test?
Write a function/method/etc. that can find the first element in a given list matching a given condition.
It should be as generic and reusable as possible.
(Of course if your programming language already provides such a feature, you can use that instead of recreating it.)
Then to demonstrate its functionality, create the data structure specified under #Data set, and perform on it the searches specified under #Test cases.
The data structure to be used contains the names and populations (in millions) of the 10 largest metropolitan areas in Africa, and looks as follows when represented in JSON:
<lang JavaScript>[
{ "name": "Lagos", "population": 21.0 }, { "name": "Cairo", "population": 15.2 }, { "name": "Kinshasa-Brazzaville", "population": 11.3 }, { "name": "Greater Johannesburg", "population": 7.55 }, { "name": "Mogadishu", "population": 5.85 }, { "name": "Khartoum-Omdurman", "population": 4.98 }, { "name": "Dar Es Salaam", "population": 4.7 }, { "name": "Alexandria", "population": 4.58 }, { "name": "Abidjan", "population": 4.4 }, { "name": "Casablanca", "population": 3.98 }
]</lang>
However, you shouldn't parse it from JSON, but rather represent it natively in your programming language.
- The top-level data structure should be an ordered collection (i.e. a list, array, vector, or similar).
- Each element in this list should be an associative collection that maps from keys to values (i.e. a struct, object, hash map, dictionary, or similar).
- Each of them has two entries: One string value with key "name", and one numeric value with key "population".
- You may rely on the list being sorted by population count, as long as you explain this to readers.
If any of that is impossible or unreasonable in your programming language, then feel free to deviate, as long as you explain your reasons in a comment above your solution.
Search | Expected result |
---|---|
Find the (zero-based) index of the first city in the list whose name is "Dar Es Salaam" | 6 |
Find the name of the first city in this list whose population is less than 5 million | Khartoum-Omdurman |
Find the population of the first city in this list whose name starts with the letter "A" | 4.58 |
If your programming language supports higher-order programming, then the most elegant way to implement the requested functionality in a generic and reusable way, might be to write a function (maybe called "find_index" or similar), that takes two arguments:
- The list to search through.
- A function/lambda/closure (the so-called "predicate"), which will be applied in turn to each element in the list, and whose boolean return value defines whether that element matches the search requirement.
If this is not the approach which would be most natural or idiomatic in your language, explain why, and show what is.
11l
<lang 11l>T City
String name Float population
F (name, population) .name = name .population = population
V cities = [
City(‘Lagos’, 21), City(‘Cairo’, 15.2), City(‘Kinshasa-Brazzaville’, 11.3), City(‘Greater Johannesburg’, 7.55), City(‘Mogadishu’, 5.85), City(‘Khartoum-Omdurman’, 4.98), City(‘Dar Es Salaam’, 4.7), City(‘Alexandria’, 4.58), City(‘Abidjan’, 4.4), City(‘Casablanca’, 3.98) ]
F first_index(cities, condition)
L(city) cities I condition(city) R L.index
F first(cities, condition)
L(city) cities I condition(city) R city
print(first_index(cities, city -> city.name == ‘Dar Es Salaam’)) print(first(cities, city -> city.population < 5.0).name) print(first(cities, city -> city.name[0] == ‘A’).population)</lang>
- Output:
6 Khartoum-Omdurman 4.58
8th
8th uses JSON as its native data representation, so using it is quite natural: <lang forth>[
{ "name": "Lagos", "population": 21.0 }, { "name": "Cairo", "population": 15.2 }, { "name": "Kinshasa-Brazzaville", "population": 11.3 }, { "name": "Greater Johannesburg", "population": 7.55 }, { "name": "Mogadishu", "population": 5.85 }, { "name": "Khartoum-Omdurman", "population": 4.98 }, { "name": "Dar Es Salaam", "population": 4.7 }, { "name": "Alexandria", "population": 4.58 }, { "name": "Abidjan", "population": 4.4 }, { "name": "Casablanca", "population": 3.98 }
] var, cities-raw
"Index of first occurrence of 'Dar Es Salaam': " . "Dar Es Salaam" >r cities-raw @ (
"name" m:@ r@ s:= if drop . cr ;; then 2drop
) a:each drop rdrop
"The name of the first city in this list whose population is less than 5 million: " . 5 >r cities-raw @ (
nip "population" m:@ r@ n:< if "name" m:@ . cr break then drop
) a:each drop rdrop
"The population of the first city in this list whose name starts with the letter \"A\": " . 'A >r cities-raw @ (
nip "name" m:@ 0 s:@ r@ n:= if drop "population" m:@ . cr break then 2drop
) a:each drop rdrop
bye</lang>
- Output:
Index of first occurrence of 'Dar Es Salaam': 6 The name of the first city in this list whose population is less than 5 million: Khartoum-Omdurman The population of the first city in this list whose name starts with the letter "A": 4.58000
Ada
This solution in inspired by how the Ada.Containers
child packages work. Usually a Cursor
contains two accesses: one to the container and one to the element. Since we want to get the index of the element as well, the index was stored instead.
<lang Ada>with Ada.Strings.Unbounded; use Ada.Strings.Unbounded; with Ada.Text_IO;
procedure Search_A_List_Of_Records is
function "+"(input : in String) return Unbounded_String renames To_Unbounded_String; function "+"(input : in Unbounded_String) return String renames To_String;
type City is record name : Unbounded_String; population : Float; end record;
type City_Array is array(Positive range <>) of City; type City_Array_Access is access City_Array;
type Cursor is record container : City_Array_Access; index : Natural; end record;
function Element(C : in Cursor) return City is begin if C.container = null or C.index = 0 then raise Constraint_Error with "No element."; end if;
return C.container.all(C.index); end Element;
function Index_0(C : in Cursor) return Natural is begin if C.container = null or C.index = 0 then raise Constraint_Error with "No element."; end if;
return C.index - C.container.all'First; end Index_0;
function Find (container : in City_Array; check : not null access function(Element : in City) return Boolean) return Cursor is begin for I in container'Range loop if check.all(container(I)) then return (new City_Array'(container), I); end if; end loop; return (null, 0); end;
function Dar_Es_Salaam(Element : in City) return Boolean is begin return Element.name = "Dar Es Salaam"; end Dar_Es_Salaam;
function Less_Than_Five_Million(Element : in City) return Boolean is begin return Element.population < 5.0; end Less_Than_Five_Million;
function Starts_With_A(Item : in City) return Boolean is begin return Element(Item.name, 1) = 'A'; end Starts_With_A;
cities : constant City_Array := ((+"Lagos", 21.0), (+"Cairo", 15.2), (+"Kinshasa-Brazzaville", 11.3), (+"Greater Johannesburg", 7.55), (+"Mogadishu", 5.85), (+"Khartoum-Omdurman", 4.98), (+"Dar Es Salaam", 4.7 ), (+"Alexandria", 4.58), (+"Abidjan", 4.4 ), (+"Casablanca", 3.98));
begin
Ada.Text_IO.Put_Line(Index_0(Find(cities, Dar_Es_Salaam'Access))'Img); Ada.Text_IO.Put_Line(+Element(Find(cities, Less_Than_Five_Million'Access)).name); Ada.Text_IO.Put_Line(Element(Find(cities, Starts_With_A'Access)).population'Img);
end Search_A_List_Of_Records;</lang>
- Output:
6 Khartoum-Omdurman 4.58000E+00
ALGOL 68
<lang algol68># Algol 68 doesn't have generic array searches but we can easily provide #
- type specific ones #
- mode to hold the city/population info #
MODE CITYINFO = STRUCT( STRING name, REAL population in millions );
- array of cities and populations #
[ 1 : 10 ]CITYINFO cities := ( ( "Lagos", 21.0 )
, ( "Cairo", 15.2 ) , ( "Kinshasa-Brazzaville", 11.3 ) , ( "Greater Johannesburg", 7.55 ) , ( "Mogadishu", 5.85 ) , ( "Khartoum-Omdurman", 4.98 ) , ( "Dar Es Salaam", 4.7 ) , ( "Alexandria", 4.58 ) , ( "Abidjan", 4.4 ) , ( "Casablanca", 3.98 ) );
- operator to find the first city with the specified criteria, expressed as a procedure #
- returns the index of the CITYINFO. We can also overload FIND so it can be applied to #
- arrays of other types #
- If there is no city matching the criteria, a value greater than the upper bound of #
- the cities array is returned #
PRIO FIND = 1; OP FIND = ( REF[]CITYINFO cities, PROC( REF CITYINFO )BOOL criteria )INT:
BEGIN INT result := UPB cities + 1; BOOL found := FALSE; FOR pos FROM LWB cities TO UPB cities WHILE NOT found DO IF criteria( cities[ pos ] ) THEN found := TRUE; result := pos FI OD; result END # FIND # ;
- convenience operator to determine whether a STRING starts with a particular character #
- returns TRUE if s starts with c, FALSE otherwise #
PRIO STARTSWITH = 9; OP STARTSWITH = ( STRING s, CHAR c )BOOL:
IF LWB s > UPB s THEN FALSE # empty string # ELSE s[ LWB s ] = c FI # STARTSWITH # ;
- find the 0-based index of Dar Es Salaam #
- ( if we remove the "[ @ 0 ]", it would find the 1-based index ) #
- NB - this assumes there is one - would get a subscript bound error if there isn't #
print( ( "index of Dar Es Salaam (from 0): "
, whole( cities[ @ 0 ] FIND ( ( REF CITYINFO city )BOOL: name OF city = "Dar Es Salaam" ), 0 ) , newline ) );
- find the first city with population under 5M #
- NB - this assumes there is one - would get a subscript bound error if there isn't #
print( ( name OF cities[ cities FIND ( ( REF CITYINFO city )BOOL: population in millions OF city < 5.0 ) ]
, " has a population under 5M" , newline ) );
- find the population of the first city whose name starts with "A" #
- NB - this assumes there is one - would get a subscript bound error if there isn't #
print( ( "The population of a city named ""A..."" is: "
, fixed( population in millions OF cities[ cities FIND ( ( REF CITYINFO city )BOOL: name OF city STARTSWITH "A" ) ], 0, 2 ) , newline ) )
</lang>
- Output:
index of Dar Es Salaam (from 0): 6 Khartoum-Omdurman has a population under 5M The population of a city named "A..." is: 4.58
AppleScript
<lang AppleScript>-- RECORDS
property lstCities : [¬
of rec = "Dar Es Salaam"
end nameIsDar -- popBelow :: Record -> Bool on popBelow5M(rec) population of rec < 5 end popBelow5M -- nameBeginsWith :: Record -> Bool on nameBeginsWithA(rec) text 1 of |name| of rec = "A" end nameBeginsWithA
return {¬ findIndex(nameIsDar, lstCities), ¬ ¬ |
of find(popBelow5M, lstCities), ¬
¬ population of find(nameBeginsWithA, lstCities)} end run
-- find :: (a -> Bool) -> [a] -> Maybe a on find(f, xs) tell mReturn(f) set lng to length of xs repeat with i from 1 to lng if lambda(item i of xs) then return item i of xs end repeat return missing value end tell end find -- findIndex :: (a -> Bool) -> [a] -> Maybe Int on findIndex(f, xs) tell mReturn(f) set lng to length of xs repeat with i from 1 to lng if lambda(item i of xs) then return i end repeat return missing value end tell end findIndex -- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: Handler -> Script on mReturn(f) if class of f is script then f else script property lambda : f end script end if end mReturn</lang>
<lang AppleScript>{6, "Khartoum-Omdurman", 4.58}</lang> AppleScriptObjectiveCWhile vanilla AppleScript doesn't provide filters for its own lists and records (and, by the way, has never officially supported square-bracket lists like the one used in the script above), its extension AppleScriptObjectiveC can filter the equivalent Foundation classes. So bridging between the classes may occasionally be useful. For efficiency, one would try to avoid repeatedly bridging the same objects. <lang applescript>use AppleScript version "2.4" -- OS X 10.10 (Yosemite) or later use framework "Foundation" -- Return the zero-based index of the first dictionary in an array which matches a given criterion or criteria. on indexOfFirstDictionaryInArray:theArray |whose|:predicateText set filter to current application's class "NSPredicate"'s predicateWithFormat:(predicateText) set filteredArray to theArray's filteredArrayUsingPredicate:(filter) if ((count filteredArray) > 0) then return (theArray's indexOfObjectIdenticalTo:(filteredArray's firstObject())) as integer else return missing value -- No match. end if end indexOfFirstDictionaryInArray:|whose|: on run local listOfRecords, arrayOfDictionaries, result1, result2, result3 set listOfRecords to {¬ Arturo<lang rebol>define :city [name population][] records: map [ ["Lagos" 21.0] ["Cairo" 15.2] ["Kinshasa-Brazzaville" 11.3] ["Greater Johannesburg" 7.55] ["Mogadishu" 5.85] ["Khartoum-Omdurman" 4.98] ["Dar Es Salaam" 4.7] ["Alexandria" 4.58] ["Abidjan" 4.4] ["Casablanca" 3.98] ] => [to :city] find: function [block f][ loop.with: 'i block 'elt [ if f elt -> return @[elt i] ] return false ]
print last find records $[c][equal? c\name "Dar Es Salaam"]
print get first find records $[c][less? c\population 5] 'name
print get first find records $[c][equal? first c\name `A`] 'population </lang>
6 Khartoum-Omdurman 4.58 CThis solution makes use of the 'bsearch' and 'lfind' library functions. Note: 'lfind' is available only on Posix systems, and is found in the 'search.h' header. However it is also part of the Ming C Compiler for Windows. <lang c>
struct cd { char *name; double population; }; /* Return -1 if name could not be found */ int search_get_index_by_name(const char *name, const struct cd *data, const size_t data_length, int (*cmp_func)(const void *, const void *)) { struct cd key = { (char *) name, 0 }; struct cd *match = bsearch(&key, data, data_length, sizeof(struct cd), cmp_func); if (match == NULL) return -1; else return ((intptr_t) match - (intptr_t) data) / sizeof(struct cd); } /* Return -1 if no matching record can be found */ double search_get_pop_by_name(const char *name, const struct cd *data, size_t data_length, int (*cmp_func)(const void *, const void *)) { struct cd key = { (char *) name, 0 }; struct cd *match = lfind(&key, data, &data_length, sizeof(struct cd), cmp_func); if (match == NULL) return -1; else return match->population; } /* Return NULL if no value satisfies threshold */ char* search_get_pop_threshold(double pop_threshold, const struct cd *data, size_t data_length, int (*cmp_func)(const void *, const void *)) { struct cd key = { NULL, pop_threshold }; struct cd *match = lfind(&key, data, &data_length, sizeof(struct cd), cmp_func); if (match == NULL) return NULL; else return match->name; } int cd_nameChar_cmp(const void *a, const void *b) { struct cd *aa = (struct cd *) a; struct cd *bb = (struct cd *) b; int i,len = strlen(aa->name); for(i=0;i<len;i++) if(bb->name[i]!=aa->name[i]) return -1; return 0; } int cd_name_cmp(const void *a, const void *b) { struct cd *aa = (struct cd *) a; struct cd *bb = (struct cd *) b; return strcmp(bb->name, aa->name); } int cd_pop_cmp(const void *a, const void *b) { struct cd *aa = (struct cd *) a; struct cd *bb = (struct cd *) b; return bb->population >= aa->population; } int main(void) { const struct cd citydata[] = { { "Lagos", 21 }, { "Cairo", 15.2 }, { "Kinshasa-Brazzaville", 11.3 }, { "Greater Johannesburg", 7.55 }, { "Mogadishu", 5.85 }, { "Khartoum-Omdurman", 4.98 }, { "Dar Es Salaam", 4.7 }, { "Alexandria", 4.58 }, { "Abidjan", 4.4 }, { "Casablanca", 3.98 } }; const size_t citydata_length = LEN(citydata); printf("%d\n", search_get_index_by_name("Dar Es Salaam", citydata, citydata_length, cd_name_cmp)); printf("%s\n", search_get_pop_threshold(5, citydata, citydata_length, cd_pop_cmp)); printf("%lf\n", search_get_pop_by_name("A", citydata, citydata_length, cd_nameChar_cmp)); return 0; } </lang> Output 6 Khartoum-Omdurman 4.580000 C#<lang csharp>using System; using System.Collections.Generic; namespace RosettaSearchListofRecords { class Program { static void Main(string[] args) { var dataset = new List<Dictionary<string, object>>() { new Dictionary<string, object> {{ "name" , "Lagos"}, {"population", 21.0 }}, new Dictionary<string, object> {{ "name" , "Cairo"}, {"population", 15.2 }}, new Dictionary<string, object> {{ "name" , "Kinshasa-Brazzaville"}, {"population", 11.3 }}, new Dictionary<string, object> {{ "name" , "Greater Johannesburg"}, {"population", 7.55 }}, new Dictionary<string, object> {{ "name" , "Mogadishu"}, {"population", 5.85 }}, new Dictionary<string, object> {{ "name" , "Khartoum-Omdurman"}, {"population", 4.98 }}, new Dictionary<string, object> {{ "name" , "Dar Es Salaam"}, {"population", 4.7 }}, new Dictionary<string, object> {{ "name" , "Alexandria"}, {"population", 4.58 }}, new Dictionary<string, object> {{ "name" , "Abidjan"}, {"population", 4.4 }}, new Dictionary<string, object> {{ "name" , "Casablanca"}, {"population", 3.98 }} }; // Find the (zero-based) index of the first city in the list whose name is "Dar Es Salaam" var index = dataset.FindIndex(x => ((string)x["name"]) == "Dar Es Salaam"); Console.WriteLine(index); // Find the name of the first city in this list whose population is less than 5 million var name = (string)dataset.Find(x => (double)x["population"] < 5.0)["name"]; Console.WriteLine(name); // Find the population of the first city in this list whose name starts with the letter "A" var aNamePopulation = (double)dataset.Find(x => ((string)x["name"]).StartsWith("A"))["population"]; Console.WriteLine(aNamePopulation); } } }</lang>
6 Khartoum-Omdurman 4.58 C++std::find_if accepts a lambda as predicate. <lang cpp>#include <iostream>
struct city { std::string name; float population; }; int main() { std::vector<city> cities = { { "Lagos", 21 }, { "Cairo", 15.2 }, { "Kinshasa-Brazzaville", 11.3 }, { "Greater Johannesburg", 7.55 }, { "Mogadishu", 5.85 }, { "Khartoum-Omdurman", 4.98 }, { "Dar Es Salaam", 4.7 }, { "Alexandria", 4.58 }, { "Abidjan", 4.4 }, { "Casablanca", 3.98 }, }; auto i1 = std::find_if( cities.begin(), cities.end(), [](city c){ return c.name == "Dar Es Salaam"; } ); if (i1 != cities.end()) { std::cout << i1 - cities.begin() << "\n"; } auto i2 = std::find_if( cities.begin(), cities.end(), [](city c){ return c.population < 5.0; } ); if (i2 != cities.end()) { std::cout << i2->name << "\n"; } auto i3 = std::find_if( cities.begin(), cities.end(), [](city c){ return c.name.length() > 0 && c.name[0] == 'A'; } ); if (i3 != cities.end()) { std::cout << i3->population << "\n"; } }</lang>
6 Khartoum-Omdurman 4.58
ClojureIn order to not rely on the input ordering of the data records, this example adds an "idx" value to the records, for purposes of being able to report the answer to the queries which rely on the original ordering. The data records are then re-sorted to be ordered by city name. This helps to make it clear that the query relying on sort-by-population is properly handled in the query itself. <lang Clojure>(def records [{:idx 8, :name "Abidjan", :population 4.4} {:idx 7, :name "Alexandria", :population 4.58} {:idx 1, :name "Cairo", :population 15.2} {:idx 9, :name "Casablanca", :population 3.98} {:idx 6, :name "Dar Es Salaam", :population 4.7} {:idx 3, :name "Greater Johannesburg", :population 7.55} {:idx 5, :name "Khartoum-Omdurman", :population 4.98} {:idx 2, :name "Kinshasa-Brazzaville", :population 11.3} {:idx 0, :name "Lagos", :population 21.0} {:idx 4, :name "Mogadishu", :population 5.85}]) (defn city->idx [recs city] (-> (some #(when (= city (:name %)) %) recs) :idx)) (defn rec-with-max-population-below-n [recs limit] (->> (sort-by :population > recs) (drop-while (fn [r] (>= (:population r) limit))) first)) (defn most-populous-city-below-n [recs limit] (:name (rec-with-max-population-below-n recs limit)))</lang>
(city->idx records "Dar Es Salaam") ; 6 (most-populous-city-below-n records 5.0) ; "Khartoum-Omdurman" (->> (sort-by :idx records) (drop-while #(not (clojure.string/starts-with? (:name %) "A"))) first :population) ; 4.58 Common Lisp<lang lisp>(defstruct city (name nil :type string) (population nil :type number)) (defparameter *cities* (list (make-city :name "Lagos" :population 21.0) (make-city :name "Cairo" :population 15.2) (make-city :name "Kinshasa-Brazzaville" :population 11.3) (make-city :name "Greater Johannesburg" :population 7.55) (make-city :name "Mogadishu" :population 5.85) (make-city :name "Khartoum-Omdurman" :population 4.98) (make-city :name "Dar Es Salaam" :population 4.7) (make-city :name "Alexandria" :population 4.58) (make-city :name "Abidjan" :population 4.4) (make-city :name "Casablanca" :population 3.98))) (defun main () (let ((answer1 (position "Dar Es Salaam" *cities* :key #'city-name :test #'string=)) (answer2 (city-name (find-if (lambda (population) (< population 5)) *cities* :key #'city-population))) (answer3 (city-population (find-if (lambda (name) (char= (char name 0) #\A)) *cities* :key #'city-name)))) (format t "Answer 1: ~A~%" answer1) (format t "Answer 2: ~A~%" answer2) (format t "Answer 3: ~A~%" answer3)))</lang>
Answer 1: 6 Answer 2: Khartoum-Omdurman Answer 3: 4.58 EchoLispWe demonstrate the vector-search primitive, which takes as input a vector, and a predicate. <lang scheme> (require 'struct) (require 'json)
(define cities
[{"name":"Lagos", "population":21}, {"name":"Cairo", "population":15.2}, {"name":"Kinshasa-Brazzaville", "population":11.3}, {"name":"Greater Johannesburg", "population":7.55}, {"name":"Mogadishu", "population":5.85}, {"name":"Khartoum-Omdurman", "population":4.98}, {"name":"Dar Es Salaam", "population":4.7}, {"name":"Alexandria", "population":4.58}, {"name":"Abidjan", "population":4.4}, {"name":"Casablanca", "population":3.98}] >>#)
(struct city (name population))
(set! cities (vector-map (lambda(x) (json->struct x struct:city)) (json-import cities)))
(define (city-index name) (vector-search (lambda(x) (string-ci=? (city-name x) name)) cities))
(define (city-pop seuil) (define idx (vector-search (lambda(x) (< (city-population x) seuil)) cities)) (if idx (city-name (vector-ref cities idx)) (cons seuil 'not-found)))
ElenaELENA 5.0 : <lang elena>import extensions; import system'routines; public program() { var dataset := new object[] { new { Name = "Lagos"; Population = 21.0r; }, new { Name = "Cairo"; Population = 15.2r; }, new { Name = "Kinshasa-Brazzaville"; Population = 11.3r; }, new { Name = "Greater Johannesburg"; Population = 7.55r; }, new { Name = "Mogadishu"; Population = 5.85r; }, new { Name = "Khartoum-Omdurman"; Population = 4.98r; }, new { Name = "Dar Es Salaam"; Population = 4.7r; }, new { Name = "Alexandria"; Population = 4.58r; }, new { Name = "Abidjan"; Population = 4.4r; }, new { Name = "Casablanca"; Population = 3.98r; } }; var index := dataset.selectBy:(r => r.Name).toArray().indexOfElement("Dar Es Salaam"); console.printLine(index); var name := dataset.filterBy:(c => c.Population < 5.0r).toArray().FirstMember.Name; console.printLine(name); var namePopulation := dataset.filterBy:(c => c.Name.startingWith("A")).toArray().FirstMember.Population; console.printLine(namePopulation) }</lang>
6 Khartoum-Omdurman 4.58 Elixir<lang elixir>cities = [ [name: "Lagos", population: 21.0 ], [name: "Cairo", population: 15.2 ], [name: "Kinshasa-Brazzaville", population: 11.3 ], [name: "Greater Johannesburg", population: 7.55], [name: "Mogadishu", population: 5.85], [name: "Khartoum-Omdurman", population: 4.98], [name: "Dar Es Salaam", population: 4.7 ], [name: "Alexandria", population: 4.58], [name: "Abidjan", population: 4.4 ], [name: "Casablanca", population: 3.98] ] IO.puts Enum.find_index(cities, fn city -> city[:name] == "Dar Es Salaam" end) IO.puts Enum.find(cities, fn city -> city[:population] < 5.0 end)[:name] IO.puts Enum.find(cities, fn city -> String.first(city[:name])=="A" end)[:population]</lang>
6 Khartoum-Omdurman 4.58 FactorFor our associative structure, we use the tuple: an object composed of named slots, each holding a value which can be accessed using automatically-generated accessors. Factor is built around combinators (Factor's word for higher-order functions), so completing the task as requested is idiomatic. Not only does TUPLE: city name pop ; CONSTANT: data { T{ city f "Lagos" 21.0 } T{ city f "Cairo" 15.2 } T{ city f "Kinshasa-Brazzaville" 11.3 } T{ city f "Greater Johannesburg" 7.55 } T{ city f "Mogadishu" 5.85 } T{ city f "Khartoum-Omdurman" 4.98 } T{ city f "Dar Es Salaam" 4.7 } T{ city f "Alexandria" 4.58 } T{ city f "Abidjan" 4.4 } T{ city f "Casablanca" 3.98 } } | ||||||||
Print the index of the first city named Dar Es Salaam.
data [ name>> "Dar Es Salaam" = ] find drop . |
Print the name of the first city with under 5 million people.
data [ pop>> 5 < ] find nip name>> print |
Print the population of the first city starting with 'A'.
data [ name>> first CHAR: A = ] find nip pop>> .</lang>
6 Khartoum-Omdurman 4.58 FortranIn order to employ a compound data aggregate such as CITY with components CITY.NAME and CITY.POPULATION, F90 is required. Earlier, one would have employed a collection of separate arrays with similar names, such as CNAME and CPOP. This may still be desirable when array parameters from a data aggregate will be passed via copy-in and copy-out instead of by reference. An alternative declaration would be to have the components of the aggregate use the array aspect, as in As for the names, one must choose a maximum size for the city name, and 28 seems a perfect choice, even for names in Madagascar. Later fortran offers facilities for character variables "fitted to size", at the cost of extra indirection. Fortran does not offer a "pass-by-name" facility, whereby the test function for the searches could be specified in the manner of Jensen's_Device, something like Instead, two search functions. Using the function's name as a variable within the function could not be relied on prior to F90: some compilers would disallow it and in other cases odd results might be produced, so a local variable would have to be used. These functions turn out to be general in the sense that they're not limited to a type of CITYSTAT. Instead, FIRSTMATCH searches an array of texts, and FIRSTLESS an array of floating-point numbers - they could be applied to any such arrays. But sometimes at a cost. They are not prepared to deal with arrays having a "stride" other than one, such as the CITY.NAME entries, whose successive elements are not in successive storage locations. Instead, the compiler generates code to copy the desired elements from the CITY aggregate into a temporary variable having that arrangement, and passes that to the routine by reference. One could use the special declaration Although F90 allows an array to be defined with a lower bound other than the default of one, this requires such a non-default lower bound to be specified in every declaration, which is tiresome, and leads to confusion over counting. Still, to suit the requirement, the index found for Dar Es Salaam is reduced by one. Returning a value of zero for "not found" is helpful (-1 would be good too, but this can't be an unsigned integer) and it is often useful to have an actual element zero with a dummy entry, such as The specification mentions an ordered list: here, the items are indeed ordered in storage (as first, second, etc) but ordering more usefully refers to the values of the components. The example is presented in reducing order of population. More generally, the storage order might be arbitrary, and one would use indices, arrays such as XCNAME which would list the entries in the order of their names, and XCPOP their populations. These arrays would each be produced by an indexed sort process that would not move the data about, and so long as entries were not frequently altered (requiring re-sorting) these indices could be used for searching. Such arrays involve the ability to access an individual city's information at random, simply by specifying the index into the CITY array, however the given problem requires only sequential access. In such a case, the storage for the city elements could be formed as a linked-list which would be followed sequentially. Even so, random access can be regained via an array such as XCNAME, which now would hold the storage address of the corresponding CITY element. And as ever, how long is a piece of string? Here, ten. If the data were stored as records in a disc file, a record zero won't exist and so appropriate testing for "not found" will be required. For this example however there is no attempt either to prepare a suitable "not found" entry nor to test and evade such a misfortune. The test data employed do not provoke such errors... <lang Fortran> MODULE SEMPERNOVIS !Keep it together. TYPE CITYSTAT !Define a compound data type. CHARACTER*28 NAME !Long enough? REAL POPULATION !Accurate enough. END TYPE CITYSTAT !Just two parts, but different types. TYPE(CITYSTAT) CITY(10) !Righto, I'll have some. DATA CITY/ !Supply the example's data. 1 CITYSTAT("Lagos", 21.0 ), 2 CITYSTAT("Cairo", 15.2 ), 3 CITYSTAT("Kinshasa-Brazzaville",11.3 ), 4 CITYSTAT("Greater Johannesburg", 7.55), 5 CITYSTAT("Mogadishu", 5.85), 6 CITYSTAT("Khartoum-Omdurman", 4.98), 7 CITYSTAT("Dar Es Salaam", 4.7 ), 8 CITYSTAT("Alexandria", 4.58), 9 CITYSTAT("Abidjan", 4.4 ), o CITYSTAT("Casablanca", 3.98)/ CONTAINS INTEGER FUNCTION FIRSTMATCH(TEXT,TARGET) !First matching. CHARACTER*(*) TEXT(:) !An array of texts. CHARACTER*(*) TARGET !The text to look for. DO FIRSTMATCH = 1,UBOUND(TEXT,DIM = 1) !Scan the array from the start. IF (TEXT(FIRSTMATCH) .EQ. TARGET) RETURN !An exact match? Ignoring trailing spaces. END DO !Try the next. FIRSTMATCH = 0 !No match. Oh dear. END FUNCTION FIRSTMATCH INTEGER FUNCTION FIRSTLESS(VAL,TARGET) !First matching. REAL VAL(:) !An array of values. REAL TARGET !The value to look for. DO FIRSTLESS = 1,UBOUND(VAL,DIM = 1) !Step through the array from the start. IF (VAL(FIRSTLESS) .LT. TARGET) RETURN !Suitable? END DO !Try the next. FIRSTLESS = 0 !No match. Oh dear. END FUNCTION FIRSTLESS END MODULE SEMPERNOVIS PROGRAM POKE USE SEMPERNOVIS !Ex Africa, ... CHARACTER*(*) BLAH !Save on some typing. PARAMETER (BLAH = "The first city in the list whose ") !But also, for layout. WRITE (6,1) BLAH,FIRSTMATCH(CITY.NAME,"Dar Es Salaam") - 1 !My array starts with one. 1 FORMAT (A,"name is Dar Es Salaam, counting with zero, is #",I0) WRITE (6,2) BLAH,CITY(FIRSTLESS(CITY.POPULATION,5.0)).NAME 2 FORMAT (A,"population is less than 5 is ",A) WRITE (6,3) BLAH,CITY(FIRSTMATCH(CITY.NAME(1:1),"A")).POPULATION 3 FORMAT (A,"whose name starts with A has population",F5.2) END</lang> The words NAME and TARGET can have special usages in F90, but fortran has no reserved words so these names can be put to ordinary use. Alas, the syntax highlighter does not recognise their non-special use and gives them colour. One could fuss further over the layout of the output, but here it is: The first city in the list whose name is Dar Es Salaam, counting with zero, is #6 The first city in the list whose population is less than 5 is Khartoum-Omdurman The first city in the list whose whose name starts with 'A' has population 4.58 GoBasic solution: <lang go>package main import ( "fmt" "strings" ) type element struct { name string population float64 } var list = []element{ {"Lagos", 21}, {"Cairo", 15.2}, {"Kinshasa-Brazzaville", 11.3}, {"Greater Johannesburg", 7.55}, {"Mogadishu", 5.85}, {"Khartoum-Omdurman", 4.98}, {"Dar Es Salaam", 4.7}, {"Alexandria", 4.58}, {"Abidjan", 4.4}, {"Casablanca", 3.98}, } func find(cond func(*element) bool) int { for i := range list { if cond(&list[i]) { return i } } return -1 } func main() { fmt.Println(find(func(e *element) bool { return e.name == "Dar Es Salaam" })) i := find(func(e *element) bool { return e.population < 5 }) if i < 0 { fmt.Println("*** not found ***") } else { fmt.Println(list[i].name) } i = find(func(e *element) bool { return strings.HasPrefix(e.name, "A") }) if i < 0 { fmt.Println("*** not found ***") } else { fmt.Println(list[i].population) } }</lang>
6 Khartoum-Omdurman 4.58 Data conversion solution: The prohibition on parsing JSON is unreasonable in any language. The alternative to parsing by computer is parsing manually, reformatting data with human fingers on a keyboard. It's okay for ten lines of test data but would be unreasonable in any real application. But let's say than in real life you have a pointy-haired boss that decrees that no JSON parsing will be done — even though he has contracted a vendor that supplies JSON only. You would write a data converter that quietly converts data outside the application. First, a package to define the data structure needed. This package will be imported by both the data conversion tool and the application. <lang go>package datadef type Element struct { Name string Population float64 } type List []Element</lang> Then the data conversion tool. This program reads JSON from stdin and generates the Go code of a package "data" containing an equivalent Go literal. <lang go>package main import ( "encoding/json" "fmt" "go/build" "log" "os" "path/filepath" "datadef" ) func main() { var l datadef.List if err := json.NewDecoder(os.Stdin).Decode(&l); err != nil { log.Fatal(err) } pp := filepath.Join(filepath.SplitList(build.Default.GOPATH)[0], "src/data") f, err := os.Create(filepath.Join(pp, "data.go")) if err != nil { log.Fatal(err) } fmt.Fprintln(f, `package data import "datadef" var List = datadef.List {`) for i, e := range l { fmt.Fprintf(f, " %d: {%q, %g},\n", i, e.Name, e.Population) } fmt.Fprintln(f, "}") }</lang>
<lang go>package data import "datadef" var List = datadef.List { 0: {"Lagos", 21}, 1: {"Cairo", 15.2}, 2: {"Kinshasa-Brazzaville", 11.3}, 3: {"Greater Johannesburg", 7.55}, 4: {"Mogadishu", 5.85}, 5: {"Khartoum-Omdurman", 4.98}, 6: {"Dar Es Salaam", 4.7}, 7: {"Alexandria", 4.58}, 8: {"Abidjan", 4.4}, 9: {"Casablanca", 3.98}, }</lang> The desired program imports the generated package containing the converted data. Program and imported data are JSON-free. <lang go>package main import ( "fmt" "strings" "data" "datadef" ) func find(cond func(*datadef.Element) bool) int { for i := range data.List { if cond(&data.List[i]) { return i } } return -1 } func main() { i := find(func(e *datadef.Element) bool { return e.Name == "Dar Es Salaam" }) if i < 0 { fmt.Println("*** not found ***") } else { fmt.Println(i) } i = find(func(e *datadef.Element) bool { return e.Population < 5 }) if i < 0 { fmt.Println("*** not found ***") } else { fmt.Println(data.List[i].Name) } i = find(func(e *datadef.Element) bool { return strings.HasPrefix(e.Name, "A") }) if i < 0 { fmt.Println("*** not found ***") } else { fmt.Println(data.List[i].Population) } }</lang> Output same as basic solution. Solution using sorted population count: The population ordering is useful only for queries against population and so cannot be used, at least not in any simple way, by the general find function shown above. The sort package of the Go standard library however contains a function for making general queries against an ordered list. This solution shows how the population query can be done with this function. <lang go>package main import ( "fmt" "sort" "data" ) func main() { if !sort.SliceIsSorted(data.List, func(i, j int) bool { return data.List[i].Population > data.List[j].Population }) { panic("data not sorted by decreasing population") } i := sort.Search(len(data.List), func(i int) bool { return data.List[i].Population < 5 }) if i == len(data.List) { fmt.Println("*** not found ***") } else { fmt.Println(data.List[i].Name) } }</lang>
Khartoum-Omdurman sort.Search for the other queries: The same sort.Search function is general enough to be used for the other two queries of the task as long as appropriate indexes are constructed. sort.Search is interesting because it is in the standard library and is much like the function required by the task, being generalized to take a function as an argument. It does not completely meet task requirements though because it works on a single ordering that must already exist or already be computed. A function that would analyze a general query, use available orderings when possible, and fall back on linear search otherwise is surely beyond the task scope. <lang go>package main import ( "fmt" "sort" "strings" "data" ) func main() { nx := make([]int, len(data.List)) for i := range nx { nx[i] = i } sort.Slice(nx, func(i, j int) bool { return data.List[nx[i]].Name < data.List[nx[j]].Name }) i := sort.Search(len(nx), func(i int) bool { return data.List[nx[i]].Name >= "Dar Es Salaam" }) if i == len(nx) || data.List[nx[i]].Name != "Dar Es Salaam" { fmt.Println("*** not found ***") } else { fmt.Println(nx[i]) } for i := range nx { nx[i] = i } sort.SliceStable(nx, func(i, j int) bool { return data.List[nx[i]].Name[0] < data.List[nx[j]].Name[0] }) i = sort.Search(len(nx), func(i int) bool { return data.List[nx[i]].Name >= "A" }) if i == len(nx) || !strings.HasPrefix(data.List[nx[i]].Name, "A") { fmt.Println("*** not found ***") } else { fmt.Println(data.List[nx[i]].Population) } }</lang>
6 4.58 Haskell<lang Haskell>import Data.List (findIndex, find) data City = City { name :: String , population :: Float } deriving (Read, Show) -- CITY PROPERTIES ------------------------------------------------------------ cityName :: City -> String cityName (City x _) = x cityPop :: City -> Float cityPop (City _ x) = x mbCityName :: Maybe City -> Maybe String mbCityName (Just x) = Just (cityName x) mbCityName _ = Nothing mbCityPop :: Maybe City -> Maybe Float mbCityPop (Just x) = Just (cityPop x) mbCityPop _ = Nothing -- EXAMPLES ------------------------------------------------------------------- mets :: [City] mets = [ City { name = "Lagos" , population = 21.0 } , City { name = "Cairo" , population = 15.2 } , City { name = "Kinshasa-Brazzaville" , population = 11.3 } , City { name = "Greater Johannesburg" , population = 7.55 } , City { name = "Mogadishu" , population = 5.85 } , City { name = "Khartoum-Omdurman" , population = 4.98 } , City { name = "Dar Es Salaam" , population = 4.7 } , City { name = "Alexandria" , population = 4.58 } , City { name = "Abidjan" , population = 4.4 } , City { name = "Casablanca" , population = 3.98 } ] -- TEST ----------------------------------------------------------------------- main :: IO () main = do mbPrint $ findIndex (("Dar Es Salaam" ==) . cityName) mets mbPrint $ mbCityName $ find ((< 5.0) . cityPop) mets mbPrint $ mbCityPop $ find (("A" ==) . take 1 . cityName) mets mbPrint :: Show a => Maybe a -> IO () mbPrint (Just x) = print x mbPrint x = print x</lang>
6 "Khartoum-Omdurman" 4.58 JTo represent the data in the task description, we will be using a tabular format as follows: <lang J>colnumeric=: 0&".&.>@{`[`]} data=: 1 colnumeric |: fixcsv 0 :0 Lagos, 21 Cairo, 15.2 Kinshasa-Brazzaville, 11.3 Greater Johannesburg, 7.55 Mogadishu, 5.85 Khartoum-Omdurman, 4.98 Dar Es Salaam, 4.7 Alexandria, 4.58 Abidjan, 4.4 Casablanca, 3.98 )</lang> And here are the required computations: <lang J> (0 { data) i. <'Dar Es Salaam' 6 (i. >./)@(* 5&>)@:>@{: data 5 5 {:: 0 {data Khartoum-Omdurman (1 { data) {::~ 'A' i.~ {.&> 0 { data 4.58</lang> The "general search function" mentioned in the task does not seem a natural fit for this set of data, because of the multi-column nature of this data. Nevertheless, we could for example define: <lang j>gsf=: 1 :0 I. u x { y )</lang> This uses the single argument aspect of the definition of Thus, we could say: <lang J> 1 (= >./)@(* 5&>)@:> gsf data 5</lang> But this doesn't seem any clearer or more concise than our previous expression which finds the index of the first example of the most populous city with a population less than five million. Not only that, but if there were multiple cities which had the same population number which satisfied this constraint, this version would return all of those indices where the task explicitly required we return the first example. J: Another approachThe following approach is arguably more natural in J than requiring a dictionary-type structure. <lang j> city=: <;._1 ';Lagos;Cairo;Kinshasa-Brazzaville;Greater Johannesburg;Mogadishu;Khartoum-Omdurman;Dar Es Salaam;Alexandria;Abidjan;Casablanca' popln=: 21 15.2 11.3 7.55 5.85 4.98 4.7 4.58 4.4 3.98 city i. <'Dar Es Salaam' NB. index of Dar Es Salaam 6 (city i. boxopen) 'Dar Es Salaam' NB. anonymous search function with city name as argument 6 city {::~ (popln < 5) {.@# \: popln NB. name of first city with population less than 5 million Khartoum-Omdurman popln&(city {::~ \:@[ {.@#~ <) 5 NB. anonymous search function with popln limit as argument Khartoum-Omdurman popln {~ 'A' i.~ {.&> city NB. population of first city whose name starts with "A" 4.58 (popln {~ ({.&> city)&i.) 'A' NB. anonymous search function with first letter as argument 4.58</lang> JavaJava (up to and including) version 7 was not capable of using Predicates or the mentioned higher-order-Programming without external libraries. Java 8 introduced Predicated and Streams (not to be confused with the Java-IO-Streams!) that changed the way how collections of objects can be processed. This example illustrates the changes by solving the three subtasks in different ways:
<lang Java>import java.util.Arrays; import java.util.Collections; import java.util.List; import java.util.function.Consumer; import java.util.function.Predicate; /** * Represent a City and it's population. * City-Objects do have a natural ordering, they are ordered by their poulation (descending) */ class City implements Comparable<City> { private final String name; private final double population; City(String name, double population) { this.name = name; this.population = population; } public String getName() { return this.name; } public double getPopulation() { return this.population; } @Override public int compareTo(City o) { //compare for descending order. for ascending order, swap o and this return Double.compare(o.population, this.population); } } public class SearchListOfRecords { public static void main(String[] args) { //Array-of-City-Objects-Literal City[] datasetArray = {new City("Lagos", 21.), new City("Cairo", 15.2), new City("Kinshasa-Brazzaville", 11.3), new City("Greater Johannesburg", 7.55), new City("Mogadishu", 5.85), new City("Khartoum-Omdurman", 4.98), new City("Dar Es Salaam", 4.7), new City("Alexandria", 4.58), new City("Abidjan", 4.4), new City("Casablanca", 3.98)}; //Since this is about "collections smarter that arrays", the Array is converted to a List List<City> dataset = Arrays.asList(datasetArray); //the City-Objects know that they are supposed to be compared by population Collections.sort(dataset);
//Find the first City that matches the given predicate and print it's index in the dataset //the Predicate here is given in the form a Java 8 Lambda that returns true if the given name //Note that the Predicate is not limited to searching for names. It can operate on anything one can done with // and compared about City-Objects System.out.println(findIndexByPredicate(dataset, city -> city.getName().equals("Dar Es Salaam"))); //Find the first City whose population matches the given Predicate (here: population <= 5.) and print it's name //here the value is returned an printed by the caller System.out.println(findFirstCityByPredicate(dataset, city -> city.getPopulation() <= 5.)); //Find the first City that matches the given predicate (here: name starts with "A") and //apply the given consumer (here: print the city's population) //here the caller specifies what to do with the object. This is the most generic solution and could also be used to solve Task 2 applyConsumerByPredicate(dataset, city -> city.getName().startsWith("A"), city -> System.out.println(city.getPopulation())); } /** * Finds a City by Predicate. * The predicate can be anything that can be done or compared about a City-Object.* * Since the task was to "find the index" it is not possible to use Java 8's stream facilities to solve this. * The Predicate is used very explicitly here - this is unusual. * * @param dataset the data to operate on, assumed to be sorted * @param p the Predicate that wraps the search term. * @return the index of the City in the dataset */ public static int findIndexByPredicate(List<City> dataset, Predicate<City> p) { for (int i = 0; i < dataset.size(); i++) { if (p.test(dataset.get(i))) return i; } return -1; } /** * Finds and returns the name of the first City where the population matches the Population-Predicate. * This solutions makes use of Java 8's stream facilities. * * @param dataset the data to operate on, assumed to be sorted * @param predicate a predicate that specifies the city searched. Can be "any predicate that can be applied to a City" * @return the name of the first City in the dataset whose population matches the predicate */ private static String findFirstCityByPredicate(List<City> dataset, Predicate<City> predicate) { //turn the List into a Java 8 stream, so it can used in stream-operations //filter() by the specified predicate (to the right of this operation, only elements matching the predicate are left in the stream) //find the first element (which is "the first city..." from the task) //get() the actualy object (this is necessary because it is wrapped in a Java 8 Optional<T> //getName() the name and return it. return dataset.stream().filter(predicate).findFirst().get().getName(); } /** * In specified dataset, find the first City whose name matches the specified predicate, and apply the specified consumer * * Since this can be solved pretty much like the "find a city by population", this has been varied. The caller specifies what to do with the result. * So this method does not return anything, but requiers a "consumer" that processes the result. * * @param dataset the data to operate on, assumed to be sorted * @param predicate a predicate that specifies the city searched. Can be "any predicate that can be applied to a City" * @param doWithResult a Consumer that specified what to do with the results */ private static void applyConsumerByPredicate(List<City> dataset, Predicate<City> predicate, Consumer<City> doWithResult) { //turn the List in to a Java 8 stream in stream-operations //filter() by the specified predicate (to the right of this operation, only elements matching the predicate are left in the stream) //find the first element (which is "the first city..." from the task) // if there is an element found, feed it to the Consumer dataset.stream().filter(predicate).findFirst().ifPresent(doWithResult); } } </lang>
6 Khartoum-Omdurman 4.58 JavaScriptES5<lang JavaScript>(function () { 'use strict'; // find :: (a -> Bool) -> [a] -> Maybe a function find(f, xs) { for (var i = 0, lng = xs.length; i < lng; i++) { if (f(xs[i])) return xs[i]; } return undefined; } // findIndex :: (a -> Bool) -> [a] -> Maybe Int function findIndex(f, xs) { for (var i = 0, lng = xs.length; i < lng; i++) { if (f(xs[i])) return i; } return undefined; } var lst = [ { "name": "Lagos", "population": 21.0 }, { "name": "Cairo", "population": 15.2 }, { "name": "Kinshasa-Brazzaville", "population": 11.3 }, { "name": "Greater Johannesburg", "population": 7.55 }, { "name": "Mogadishu", "population": 5.85 }, { "name": "Khartoum-Omdurman", "population": 4.98 }, { "name": "Dar Es Salaam", "population": 4.7 }, { "name": "Alexandria", "population": 4.58 }, { "name": "Abidjan", "population": 4.4 }, { "name": "Casablanca", "population": 3.98 } ]; return { darEsSalaamIndex: findIndex(function (x) { return x.name === 'Dar Es Salaam'; }, lst), firstBelow5M: find(function (x) { return x.population < 5; }, lst) .name, firstApop: find(function (x) { return x.name.charAt(0) === 'A'; }, lst) .population }; })();</lang>
{"darEsSalaamIndex":6, "firstBelow5M":"Khartoum-Omdurman", "firstApop":4.58} ES6<lang JavaScript>(() => { 'use strict'; let lst = [ { "name": "Lagos", "population": 21.0 }, { "name": "Cairo", "population": 15.2 }, { "name": "Kinshasa-Brazzaville", "population": 11.3 }, { "name": "Greater Johannesburg", "population": 7.55 }, { "name": "Mogadishu", "population": 5.85 }, { "name": "Khartoum-Omdurman", "population": 4.98 }, { "name": "Dar Es Salaam", "population": 4.7 }, { "name": "Alexandria", "population": 4.58 }, { "name": "Abidjan", "population": 4.4 }, { "name": "Casablanca", "population": 3.98 } ]; return { darEsSalaamIndex: lst.findIndex(x => x.name === 'Dar Es Salaam'), firstBelow5M: lst.find(x => x.population < 5) .name, firstApop: lst.find(x => x.name[0] === 'A') .population }; })();</lang>
{"darEsSalaamIndex":6, "firstBelow5M":"Khartoum-Omdurman", "firstApop":4.58} jq"jq" is so-name because it is a JSON Query Language, and thus all the abstractions are already available for the given searches, except that early versions of jq do not have `first/1` as a builtin. If your jq does not define `first/1`, then for present purposes, an appropriate definition would be: <lang jq>def first(s): [s][0];</lang> This will emit `null` if the stream, s, is empty. In each case where `first/1` is used below, a less efficient alternative is also shown. Find the (zero-based) index of the first city in the list whose name is "Dar Es Salaam"map(.name) | index("Dar Es Salaam") Find the name of the first city in this list whose population is less than 5 millionfirst(.[] | select(.population < 5)) | .name # Alternatively: map(select(.population < 5)) | .[0] | .name Find the population of the first city in this list whose name starts with the letter "A"first(.[] | select(.name[0:1] == "A")) | .population # Alternatively: map(select(.name[0:1] == "A")) | .[0] | .population Julia<lang julia>using DataFrames dataset = DataFrame(name=["Lagos", "Cairo", "Kinshasa-Brazzaville", "Greater Johannesburg", "Mogadishu", "Khartoum-Omdurman", "Dar Es Salaam", "Alexandria", "Abidjan", "Casablanca"], population=[21.0, 15.2, 11.3, 7.55, 5.85, 4.98, 4.7, 4.58, 4.4, 3.98]) print("Find the (one-based) index of the first city in the list whose name is \"Dar Es Salaam\": ") println(findfirst(dataset[:name], "Dar Es Salaam")) print("Find the name of the first city in this list whose population is less than 5 million: ") println(dataset[first(find(dataset[:population] .< 5)), :name]) print("Find the population of the first city in this list whose name starts with the letter \"A\": ") println(dataset[first(find(startswith.(dataset[:name], 'A'))), :population])</lang>
Find the (one-based) index of the first city in the list whose name is "Dar Es Salaam": 7 Find the name of the first city in this list whose population is less than 5 million: Khartoum-Omdurman Find the population of the first city in this list whose name starts with the letter "A": 4.58 Kotlin<lang scala>// version 1.1.2 class City(val name: String, val pop: Double) val cities = listOf( City("Lagos", 21.0), City("Cairo", 15.2), City("Kinshasa-Brazzaville", 11.3), City("Greater Johannesburg", 7.55), City("Mogadishu", 5.85), City("Khartoum-Omdurman", 4.98), City("Dar Es Salaam", 4.7), City("Alexandria", 4.58), City("Abidjan", 4.4), City("Casablanca", 3.98) ) fun main(args: Array<String>) { val index = cities.indexOfFirst { it.name == "Dar Es Salaam" } println("Index of first city whose name is 'Dar Es Salaam' = $index") val name = cities.first { it.pop < 5.0 }.name println("Name of first city whose population is less than 5 million = $name") val pop = cities.first { it.name[0] == 'A' }.pop println("Population of first city whose name starts with 'A' = $pop") }</lang>
Index of first city whose name is 'Dar Es Salaam' = 6 Name of first city whose population is less than 5 million = Khartoum-Omdurman Population of first city whose name starts with 'A' = 4.58 Lingo<lang lingo>on findFirstRecord (data, condition) cnt = data.count repeat with i = 1 to cnt record = data[i] if value(condition) then return [#index:i-1, #record:record] end repeat end</lang> <lang lingo>data = [\ [ "name": "Lagos", "population": 21.0 ],\ [ "name": "Cairo", "population": 15.2 ],\ [ "name": "Kinshasa-Brazzaville", "population": 11.3 ],\ [ "name": "Greater Johannesburg", "population": 7.55 ],\ [ "name": "Mogadishu", "population": 5.85 ],\ [ "name": "Khartoum-Omdurman", "population": 4.98 ],\ [ "name": "Dar Es Salaam", "population": 4.7 ],\ [ "name": "Alexandria", "population": 4.58 ],\ [ "name": "Abidjan", "population": 4.4 ],\ [ "name": "Casablanca", "population": 3.98 ]\ ] q = QUOTE -- Find the (zero-based) index of the first city in the list whose name is "Dar Es Salaam" res = findFirstRecord(data, "record.name="&q&"Dar Es Salaam"&q) if listP(res) then put res.index -- 6 -- Find the name of the first city in this list whose population is less than 5 million res = findFirstRecord(data, "record.population<5") if listP(res) then put res.record.name -- "Khartoum-Omdurman" -- Find the population of the first city in this list whose name starts with the letter "A" res = findFirstRecord(data, "record.name.char[1]="&q&"A"&q) if listP(res) then put res.record.population -- 4.5800</lang> LuaLua tables are well suited as the element type for this task. The master data structure is a table of tables. <lang Lua>-- Dataset declaration local cityPops = { {name = "Lagos", population = 21.0}, {name = "Cairo", population = 15.2}, {name = "Kinshasa-Brazzaville", population = 11.3}, {name = "Greater Johannesburg", population = 7.55}, {name = "Mogadishu", population = 5.85}, {name = "Khartoum-Omdurman", population = 4.98}, {name = "Dar Es Salaam", population = 4.7}, {name = "Alexandria", population = 4.58}, {name = "Abidjan", population = 4.4}, {name = "Casablanca", population = 3.98} } -- Function to search a dataset using a custom match function function recordSearch (dataset, matchFunction) local returnValue for index, element in pairs(dataset) do returnValue = matchFunction(index, element) if returnValue then return returnValue end end return nil end -- Main procedure local testCases = { function (i, e) if e.name == "Dar Es Salaam" then return i - 1 end end, function (i, e) if e.population < 5 then return e.name end end, function (i, e) if e.name:sub(1, 1) == "A" then return e.population end end } for _, func in pairs(testCases) do print(recordSearch(cityPops, func)) end</lang>
6 Khartoum-Omdurman 4.58 Maple<lang Maple>rec := [table(["name"="Lagos","population"=21.0]), table(["name"="Cairo","population"=15.2]), table(["name"="Kinshasa-Brazzaville","population"=11.3]), table(["name"="Greater Johannesburg","population"=7.55]), table(["name"="Mogadishu","population"=5.85]), table(["name"="Khartoum-Omdurman","population"=4.98]), table(["name"="Dar Es Salaam","population"=4.7 ]), table(["name"="Alexandria","population"=4.58]), table(["name"="Abidjan","population"=4.4]), table(["name"="Casablanca","population"=3.98])]: searchRec := proc(rec, pred, operation) local i: for i to numelems(rec) do if pred(rec[i]) then return operation(rec[i],i): fi: od: end proc: searchRec(rec, x->x["name"] = "Dar Es Salaam", (x,i)->print(i-1)): # minus 1 since Maple is 1-indexed searchRec(rec, x->x["population"]<5, (x,i)->print(x["name"])): searchRec(rec, x->x["name"][1] = "A", (x,i)->print(x["population"])):</lang>
6 "Khartoum-Omdurman" 4.58 Mathematica /Wolfram Language<lang Mathematica>data = Dataset[{ <|"name" -> "Lagos", "population" -> 21.|>, <|"name" -> "Cairo", "population" -> 15.2|>, <|"name" -> "Kinshasa-Brazzaville", "population" -> 11.3|>, <|"name" -> "Greater Johannesburg", "population" -> 7.55|>, <|"name" -> "Mogadishu", "population" -> 5.85|>, <|"name" -> "Khartoum-Omdurman", "population" -> 4.98|>, <|"name" -> "Dar Es Salaam", "population" -> 4.7|>, <|"name" -> "Alexandria", "population" -> 4.58|>, <|"name" -> "Abidjan", "population" -> 4.4|>, <|"name" -> "Casablanca", "population" -> 3.98|> }] data[Position["Dar Es Salaam"], "name"][1, 1] - 1 data[Select[#population < 5 &]][1, "name"] data[Select[StringMatchQ[#name, "A*"] &]][1, "population"]</lang> NimTo solve this task, we define a template “findIt” similar to the templates provided by the standard library module “sequtils”. As First argument it accepts any collection providing a “pairs” iterator (yielding an index and a value), for instance a sequence (list) or a table (hash). The second argument of the template is a predicate, i.e. an expression containing the “it” variable. This way, the template is able to work in a lot of contexts. <lang Nim>template findIt(data, pred: untyped): int = ## Return the index of the first element in "data" satisfying ## the predicate "pred" or -1 if no such element is found. var result = -1 for i, it {.inject.} in data.pairs: if pred: result = i break result
import strutils type City = tuple[name: string; population: float] const Cities: seq[City] = @[("Lagos", 21.0), ("Cairo", 15.2), ("Kinshasa-Brazzaville", 11.3), ("Greater Johannesburg", 7.55), ("Mogadishu", 5.85), ("Khartoum-Omdurman", 4.98), ("Dar Es Salaam", 4.7), ("Alexandria", 4.58), ("Abidjan", 4.4), ("Casablanca", 3.98)] echo "Index of the first city whose name is “Dar Es Salaam”: ", Cities.findIt(it.name == "Dar Es Salaam") let idx1 = Cities.findIt(it.population < 5) echo "Name of the first city whose population is less than 5 million: ", if idx1 == -1: "<none>" else: Cities[idx1].name let idx2 = Cities.findIt(it.name.startsWith("A")) echo "Population of the first city whose name starts with the letter “A”: ", if idx2 == -1: "<none>" else: $Cities[idx2].population</lang>
Index of the first city whose name is “Dar Es Salaam”: 6 Name of the first city whose population is less than 5 million: Khartoum-Omdurman Population of the first city whose name starts with the letter “A”: 4.58 OCaml<lang ocaml>
* task. *) (* First: Definition of the record type. *) type city = { name : string; population : float } (* Second: The actual list of records containing the data. *) let cities = [ { name = "Lagos"; population = 21.0 }; { name = "Cairo"; population = 15.2 }; { name = "Kinshasa-Brazzaville"; population = 11.3 }; { name = "Greater Johannesburg"; population = 7.55 }; { name = "Mogadishu"; population = 5.85 }; { name = "Khartoum-Omdurman"; population = 4.98 }; { name = "Dar Es Salaam"; population = 4.7 }; { name = "Alexandria"; population = 4.58 }; { name = "Abidjan"; population = 4.4 }; { name = "Casablanca"; population = 3.98 } ]
* an index. Well, never mind, I make my own... *) let find_index pred = let rec doloop i = function |
[] -> raise Not_found | x :: xs -> if pred x then i else doloop (i + 1) xs
in doloop 0
* List.filter or List.find_all would return *all* the elements that satisfy the * predicate. *) let get_first pred = List.find pred
Str.string_match (Str.regexp sub) s 0
(* We use a typical dot notation to access the record fields. *) find_index (fun c -> c.name = "Dar Es Salaam") cities |
> print_int | > print_newline;
(get_first (fun c -> c.population < 5.0) cities).name |
> print_endline;
(get_first (fun c -> startswith "A" c.name) cities).population |
> print_float | > print_newline;
</lang>
6 Khartoum-Omdurman 4.58 PerlThe first function from the core module List::Util provides short-circuiting search using a block as predicate. However, it can only return the value of the found element, not its index – so for the first test-case we need to operate on the list of indices. <lang perl>use feature 'say'; use List::Util qw(first); my @cities = ( { name => 'Lagos', population => 21.0 }, { name => 'Cairo', population => 15.2 }, { name => 'Kinshasa-Brazzaville', population => 11.3 }, { name => 'Greater Johannesburg', population => 7.55 }, { name => 'Mogadishu', population => 5.85 }, { name => 'Khartoum-Omdurman', population => 4.98 }, { name => 'Dar Es Salaam', population => 4.7 }, { name => 'Alexandria', population => 4.58 }, { name => 'Abidjan', population => 4.4 }, { name => 'Casablanca', population => 3.98 }, ); my $index1 = first { $cities[$_]{name} eq 'Dar Es Salaam' } 0..$#cities; say $index1; my $record2 = first { $_->{population} < 5 } @cities; say $record2->{name}; my $record3 = first { $_->{name} =~ /^A/ } @cities; say $record3->{population};</lang>
6 Khartoum-Omdurman 4.58 The CPAN module List::MoreUtils provides the first_index function which could be used to write that first case more elegantly: <lang perl>use List::MoreUtils qw(first_index); $index1 = first_index { $_->{name} eq 'Dar Es Salaam' } @cities;</lang> Phixconstant CITY_NAME = 1, POPULATION = 2 constant municipalities = {{"Lagos",21}, {"Cairo",15.2}, {"Kinshasa-Brazzaville",11.3}, {"Greater Johannesburg",7.55}, {"Mogadishu",5.85}, {"Khartoum-Omdurman",4.98}, {"Dar Es Salaam",4.7}, {"Alexandria",4.58}, {"Abidjan",4.4}, {"Casablanca",3.98}} function searchfor(sequence s, integer rid, object user_data, bool return_index=false) for i=1 to length(s) do if rid(s[i],user_data) then return iff(return_index?i:s[i]) end if end for return 0 -- not found end function function city_named(sequence si, string city_name) return si[CITY_NAME]==city_name end function ?searchfor(municipalities,city_named,"Dar Es Salaam",true) function smaller_than(sequence si, atom population) return si[POPULATION]<population end function ?searchfor(municipalities,smaller_than,5)[CITY_NAME] function starts_with(sequence si, integer ch) return si[CITY_NAME][1]=ch end function ?searchfor(municipalities,starts_with,'A')[POPULATION] The columnize function reorganises hetrogenous data into corresponding homogenous arrays, which can make this sort of thing much simpler, at least for exact matches. constant {cities,populations} = columnize(municipalities) ?populations[find("Dar Es Salaam",cities)]
7 "Khartoum-Omdurman" 4.58 4.7 Note that Phix subscripts are 1-based, hence the output of 7 not 6. PHP<lang PHP> <?php $data_array = [ ['name' => 'Lagos', 'population' => 21.0], ['name' => 'Cairo', 'population' => 15.2], ['name' => 'Kinshasa-Brazzaville', 'population' => 11.3], ['name' => 'Greater Johannesburg', 'population' => 7.55], ['name' => 'Mogadishu', 'population' => 5.85], ['name' => 'Khartoum-Omdurman', 'population' => 4.98], ['name' => 'Dar Es Salaam', 'population' => 4.7], ['name' => 'Alexandria', 'population' => 4.58], ['name' => 'Abidjan', 'population' => 4.4], ['name' => 'Casablanca', 'population' => 3.98], ]; $found=0; $search_name = 'Dar Es Salaam'; echo "Find the (zero-based) index of the first city in the list whose name is \"$search_name\" - 6"; $index = array_search($search_name, array_column($data_array, 'name')); $population = $data_array[$index]['population']; echo "\nAnswer 1: Index: [$index] Population for $search_name is $population Million\n"; $search_val = 5; echo "\nFind the name of the first city in this list whose population is less than $search_val million - Khartoum-Omdurman"; foreach ($data_array as $index => $row) { if ($row['population'] < $search_val) { $name = $row['name']; echo "\nAnswer 2: Index [$index] Population for $row[name] is $row[population] Million\n"; break; } } $search_term = 'A'; echo "\n\nFind the population of the first city in this list whose name starts with the letter \"$search_term\" - 4.58"; foreach ($data_array as $index => $row) { if (strpos($row['name'], $search_term) === 0) { echo "\nAnswer 3: Index: [$index] Population for $row[name] is $row[population] Million\n"; break; } } echo "\nDone..."; Output: Find the (zero-based) index of the first city in the list whose name is "Dar Es Salaam" - 6 Answer 1: Index: [6] Population for Dar Es Salaam is 4.7 Million Find the name of the first city in this list whose population is less than 5 million - Khartoum-Omdurman Answer 2: Index [5] Population for Khartoum-Omdurman is 4.98 Million Find the population of the first city in this list whose name starts with the letter "A" - 4.58 Answer 3: Index: [7] Population for Alexandria is 4.58 Million Done... </lang> PicoLisp<lang PicoLisp>(scl 2) (de *Data ("Lagos" 21.0) ("Cairo" 15.2) ("Kinshasa-Brazzaville" 11.3) ("Greater Johannesburg" 7.55) ("Mogadishu" 5.85) ("Khartoum-Omdurman" 4.98) ("Dar Es Salaam" 4.7) ("Alexandria" 4.58) ("Abidjan" 4.4) ("Casablanca" 3.98) ) (test 6 (dec (index (assoc "Dar Es Salaam" *Data) *Data)) ) (test "Khartoum-Omdurman" (car (find '((L) (> 5.0 (cadr L))) *Data)) ) (test 4.58 (cadr (find '((L) (pre? "A" (car L))) *Data)) )</lang> PowerShellThe { "Name": "Lagos", "Population": 21.0 }, { "Name": "Cairo", "Population": 15.2 }, { "Name": "Kinshasa-Brazzaville", "Population": 11.3 }, { "Name": "Greater Johannesburg", "Population": 7.55 }, { "Name": "Mogadishu", "Population": 5.85 }, { "Name": "Khartoum-Omdurman", "Population": 4.98 }, { "Name": "Dar Es Salaam", "Population": 4.7 }, { "Name": "Alexandria", "Population": 4.58 }, { "Name": "Abidjan", "Population": 4.4 }, { "Name": "Casablanca", "Population": 3.98 } ] '@ $cities = $jsonData | ConvertFrom-JSON
</lang>
The
Name Population ---- ---------- Lagos 21.0 Cairo 15.2 Kinshasa-Brazzaville 11.3 Greater Johannesburg 7.55 Mogadishu 5.85 Khartoum-Omdurman 4.98 Dar Es Salaam 4.7 Alexandria 4.58 Abidjan 4.4 Casablanca 3.98 Find the index of the first city in the list whose name is "Dar Es Salaam": <lang PowerShell> $cities.Name.IndexOf("Dar Es Salaam") </lang>
6 Find the name of the first city in this list whose population is less than 5 million: <lang PowerShell> ($cities | Where-Object -Property Population -LT 5)[0].Name </lang>
Khartoum-Omdurman Find the population of the first city in this list whose name starts with the letter "A": <lang PowerShell> ($cities | Where-Object -Property Name -Match "^A")[0].Population </lang>
4.58 Python<lang Python>cities = [ { "name": "Lagos", "population": 21.0 }, { "name": "Cairo", "population": 15.2 }, { "name": "Kinshasa-Brazzaville", "population": 11.3 }, { "name": "Greater Johannesburg", "population": 7.55 }, { "name": "Mogadishu", "population": 5.85 }, { "name": "Khartoum-Omdurman", "population": 4.98 }, { "name": "Dar Es Salaam", "population": 4.7 }, { "name": "Alexandria", "population": 4.58 }, { "name": "Abidjan", "population": 4.4 }, { "name": "Casablanca", "population": 3.98 } ] def first(query): return next(query, None) print( first(index for index, city in enumerate(cities) if city['name'] == "Dar Es Salaam"), first(city['name'] for city in cities if city['population'] < 5), first(city['population'] for city in cities if city['name'][0] == 'A'), sep='\n')</lang>
6 Khartoum-Omdurman 4.58 RacketThe more idiomatic functions for the task is
(define (findf/pos proc lst) (let loop ([lst lst] [pos 0]) (cond [(null? lst) #f] [(proc (car lst)) pos] [else (loop (cdr lst) (add1 pos))]))) </lang> Now we define the list that has the data for the task. <lang Racket> (define data '(#hash((name . "Lagos") (population . 21)) #hash((name . "Cairo") (population . 15.2)) #hash((name . "Kinshasa-Brazzaville") (population . 11.3)) #hash((name . "Greater Johannesburg") (population . 7.55)) #hash((name . "Mogadishu") (population . 5.85)) #hash((name . "Khartoum-Omdurman") (population . 4.98)) #hash((name . "Dar Es Salaam") (population . 4.7)) #hash((name . "Alexandria") (population . 4.58)) #hash((name . "Abidjan") (population . 4.4)) #hash((name . "Casablanca") (population . 3.98)))) </lang> We write tiny wrappers to retrieve values from the hash. <lang Racket> (define get-name (lambda (x) (hash-ref x 'name))) (define get-population (lambda (x) (hash-ref x 'population))) </lang> For completeness, ensure the data is sorted by population largest to smallest. <lang Racket> (define sorted-data (sort data > #:key get-population)) </lang> Use an unnamed function with our findf/pos function to get the position of "Dar Es Salaam". <lang Racket> (findf/pos (lambda (x) (equal? "Dar Es Salaam" (get-name x))) sorted-data)
</lang> Use unnamed functions with findf for the other two test cases. <lang Racket> (get-name (findf (lambda (x) (< (get-population x) 5)) sorted-data))
(get-population (findf (lambda (x) (regexp-match? #rx"^A" (get-name x))) sorted-data))
</lang>
6 "Khartoum-Omdurman" 4.58 Raku(formerly Perl 6) The built-in method .first fulfills the requirements of this task. <lang perl6>my @cities = { name => 'Lagos', population => 21.0 }, { name => 'Cairo', population => 15.2 }, { name => 'Kinshasa-Brazzaville', population => 11.3 }, { name => 'Greater Johannesburg', population => 7.55 }, { name => 'Mogadishu', population => 5.85 }, { name => 'Khartoum-Omdurman', population => 4.98 }, { name => 'Dar Es Salaam', population => 4.7 }, { name => 'Alexandria', population => 4.58 }, { name => 'Abidjan', population => 4.4 }, { name => 'Casablanca', population => 3.98 }, say @cities.first(*<name> eq 'Dar Es Salaam', :k); say @cities.first(*<population> < 5).<name>; say @cities.first(*<name>.match: /^A/).<population>;</lang>
6 Khartoum-Omdurman 4.58 REXXIt is more idiomatic in REXX to use sparse arrays to express a list of CSV values, especially those which have
Most REXX interpreters use (very efficient) hashing to index sparse arrays, which is much faster than performing an
Only one loop is needed to find the result for the 2nd task requirement (although the loop could be eliminated).
The approach taken in this REXX program makes use of a DO WHILE and DO UNTIL structure which
This REXX version does not rely on the list being sorted by population count. <lang rexx>/*REXX program (when using criteria) locates values (indices) from an associate array. */ $="Lagos=21, Cairo=15.2, Kinshasa-Brazzaville=11.3, Greater Johannesburg=7.55, Mogadishu=5.85,", "Khartoum-Omdurman=4.98, Dar Es Salaam=4.7, Alexandria=4.58, Abidjan=4.4, Casablanca=3.98" @.= '(city not found)'; city.= "(no city)" /*city search results for not found.*/ /* [↓] construct associate arrays. */ do #=0 while $\=; parse var $ c '=' p "," $; c=space(c); parse var c a 2; @.c=# city.#=c; pop.#=p; pop.c=#; if @.a==@. then @.a=c; /*assign city, pop, indices.*/ end /*#*/ /* [↑] city array starts at 0 index*/ /*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ task 1: show the INDEX of a city.*/ town= 'Dar Es Salaam' /*the name of a city for the search.*/ say 'The city of ' town " has an index of: " @.town /*show (zero─based) index of a city.*/ say /*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ task 2: show 1st city whose pop<5 M*/ many=5 /*size of a city's pop in millions. */ do k=0 for # until pop.k<many; end /*find a city's pop from an index. */ say '1st city that has a population less than ' many " million is: " city.k say /*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ task 3: show 1st city with A* name.*/ c1= 'A' /*1st character of a city for search*/ say '1st city that starts with the letter' c1 "is: " @.c1 /*stick a fork in it, all done*/</lang> output when using the default inputs: The city of Dar Es Salaam has an index of: 6 1st city that has a population less than 5 million is: Khartoum-Omdurman 1st city that starts with the letter A is: Alexandria Ring<lang ring>
cities = [[:name = "Lagos",:population = 21.0 ], [:name = "Cairo",:population = 15.2 ], [:name = "Kinshasa-Brazzaville",:population = 11.3 ], [:name = "Greater Johannesburg",:population = 7.55], [:name = "Mogadishu",:population = 5.85], [:name = "Khartoum-Omdurman",:population = 4.98], [:name = "Dar Es Salaam",:population = 4.7 ], [:name = "Alexandria",:population = 4.58], [:name = "Abidjan",:population = 4.4 ], [:name = "Casablanca",:population = 3.98]] for n = 1 to len(cities) if cities[n][:name] = "Dar Es Salaam" see n-1 + nl ok next for n = 1 to len(cities) if cities[n][:population] < 5.00 see cities[n][:name] + nl exit ok next for n = 1 to len(cities) if left(cities[n][:name],1) = "A" see cities[n][:population] + nl exit ok next </lang> Output: 6 Khartoum-Omdurman 4.58 Ruby<lang Ruby>cities = [ {name: "Lagos", population: 21}, {name: "Cairo", population: 15.2}, {name: "Kinshasa-Brazzaville", population: 11.3}, {name: "Greater Johannesburg", population: 7.55}, {name: "Mogadishu", population: 5.85}, {name: "Khartoum-Omdurman", population: 4.98}, {name: "Dar Es Salaam", population: 4.7}, {name: "Alexandria", population: 4.58}, {name: "Abidjan", population: 4.4}, {name: "Casablanca", population: 3.98}, ] puts cities.index{|city| city[:name] == "Dar Es Salaam"} # => 6 puts cities.find {|city| city[:population] < 5.0}[:name] # => Khartoum-Omdurman puts cities.find {|city| city[:name][0] == "A"}[:population] # => 4.58 </lang> Rust<lang Rust>struct City { name: &'static str, population: f64, } fn main() { let cities = [ City { name: "Lagos", population: 21.0, }, City { name: "Cairo", population: 15.2, }, City { name: "Kinshasa-Brazzaville", population: 11.3, }, City { name: "Greater Johannesburg", population: 7.55, }, City { name: "Mogadishu", population: 5.85, }, City { name: "Khartoum-Omdurman", population: 4.98, }, City { name: "Dar Es Salaam", population: 4.7, }, City { name: "Alexandria", population: 4.58, }, City { name: "Abidjan", population: 4.4, }, City { name: "Casablanca", population: 3.98, }, ]; println!( "{:?}", cities.iter().position(|city| city.name == "Dar Es Salaam") ); println!( "{:?}", cities .iter() .find(|city| city.population < 5.0) .map(|city| city.name) ); println!( "{:?}", cities .iter() .find(|city| city.name.starts_with('A')) .map(|city| city.population) ); } </lang>
Some(6) Some("Khartoum-Omdurman") Some(4.58) Scala
<lang Scala>object SearchListOfRecords extends App { val cities = Vector( City("Lagos", 21.0e6), City("Cairo", 15.2e6), City("Kinshasa-Brazzaville", 11.3e6), City("Greater Johannesburg", 7.55e6), City("Mogadishu", 5.85e6), City("Khartoum-Omdurman", 4.98e6), City("Dar Es Salaam", 4.7e6), City("Alexandria", 4.58e6), City("Abidjan", 4.4e6), City("Casablanca", 3.98e6) ) def index = cities.indexWhere((_: City).name == "Dar Es Salaam") def name = cities.find(_.pop < 5.0e6).map(_.name) def pop = cities.find(_.name(0) == 'A').map(_.pop) case class City(name: String, pop: Double) println( s"Index of first city whose name is 'Dar Es Salaam' = $index\n" + s"Name of first city whose population is less than 5 million = ${name.get}\n" + f"Population of first city whose name starts with 'A' = ${pop.get}%,.0f") }</lang>
Index of first city whose name is 'Dar Es Salaam' = 6 Name of first city whose population is less than 5 million = Khartoum-Omdurman Population of first city whose name starts with 'A' = 4,580,000 SchemeHigh-level functions for finding items in lists are provided by the (srfi 1) library:
The predicate can be used to pick out the part of a compound structure we want to find. In a similar way (srfi 132) provides sorting routines with user-defined predicates: one is illustrated to ensure the list of items is sorted in decreasing population order. <lang scheme> (import (scheme base) (scheme char) (scheme write) (srfi 1) ; lists (srfi 132)) ; sorting (define-record-type <places> ; compound data type is a record with two fields (make-place name population) place? (name place-name) (population place-population)) (define *items* (list-sort ; sort by decreasing population (lambda (r1 r2) (> (place-population r1) (place-population r2))) (list (make-place "Lagos" 21.0) (make-place "Cairo" 15.2) (make-place "Kinshasa-Brazzaville" 11.3) (make-place "Greater Johannesburg" 7.55) (make-place "Mogadishu" 5.85) (make-place "Khartoum-Omdurman" 4.98) (make-place "Dar Es Salaam" 4.7) (make-place "Alexandria" 4.58) (make-place "Abidjan" 4.4) (make-place "Casablanca" 3.98))))
(display "Test 1: ") (display (list-index (lambda (item) (string=? "Dar Es Salaam" (place-name item))) *items*)) (newline)
(display "Test 2: ") (display (place-name (find (lambda (item) (< (place-population item) 5.0)) *items*))) (newline)
(display "Test 3: ") (display (place-population (find (lambda (item) (char=? (string-ref (place-name item) 0) #\A)) *items*))) (newline) </lang>
Test 1: 6 Test 2: Khartoum-Omdurman Test 3: 4.58 Sidef<lang ruby>struct City { String name, Number population, } var cities = [ City("Lagos", 21), City("Cairo", 15.2), City("Kinshasa-Brazzaville", 11.3), City("Greater Johannesburg", 7.55), City("Mogadishu", 5.85), City("Khartoum-Omdurman", 4.98), City("Dar Es Salaam", 4.7), City("Alexandria", 4.58), City("Abidjan", 4.4), City("Casablanca", 3.98), ] say cities.index{|city| city.name == "Dar Es Salaam"} say cities.first{|city| city.population < 5.0}.name say cities.first{|city| city.name.begins_with("A")}.population</lang>
6 Khartoum-Omdurman 4.58 Standard ML<lang sml>type city = { name : string, population : real } val citys : city list = [ { name = "Lagos", population = 21.0 }, { name = "Cairo", population = 15.2 }, { name = "Kinshasa-Brazzaville", population = 11.3 }, { name = "Greater Johannesburg", population = 7.55 }, { name = "Mogadishu", population = 5.85 }, { name = "Khartoum-Omdurman", population = 4.98 }, { name = "Dar Es Salaam", population = 4.7 }, { name = "Alexandria", population = 4.58 }, { name = "Abidjan", population = 4.4 }, { name = "Casablanca", population = 3.98 } ] val firstCityi = #1 (valOf (List.findi (fn (_, city) => #name(city) = "Dar Es Salaam") citys)) val firstBelow5M = #name (valOf (List.find (fn city => #population(city) < 5.0) citys)) val firstPopA = #population (valOf (List.find (fn city => String.substring (#name(city), 0, 1) = "A") citys))</lang>
val firstCityi = 6 : int val firstBelow5M = "Khartoum-Omdurman" : string val firstPopA = 4.58 : real SwiftData: <lang swift>struct Place { var name: String var population: Double } let places = [ Place(name: "Lagos", population: 21.0), Place(name: "Cairo", population: 15.2), Place(name: "Kinshasa-Brazzaville", population: 11.3), Place(name: "Greater Johannesburg", population: 7.55), Place(name: "Mogadishu", population: 5.85), Place(name: "Khartoum-Omdurman", population: 4.98), Place(name: "Dar Es Salaam", population: 4.7), Place(name: "Alexandria", population: 4.58), Place(name: "Abidjan", population: 4.4), Place(name: "Casablanca", population: 3.98) ]</lang> Using built-in methods<lang swift>guard let salaamI = places.firstIndex(where: { $0.name == "Dar Es Salaam" }) else { fatalError() } print("Dar Es Salaam has index: \(salaamI)") guard let lessThan5 = places.first(where: { $0.population < 5 }) else { fatalError() } print("First city with less than 5mil population: \(lessThan5.name)") guard let startsWithA = places.first(where: { $0.name.hasPrefix("A") }) else { fatalError() } print("Population of first city starting with A: \(startsWithA.population)")</lang>
Dar Es Salaam has index: 6 First city with less than 5mil population: Khartoum-Omdurman Population of first city starting with A: 4.58 Custom method using Key Paths<lang swift>extension Collection { func firstIndex<V: Equatable>( withProperty prop: KeyPath<Element, V>, _ op: (V, V) -> Bool, _ val: V ) -> Index? { for i in indices where op(self[i][keyPath: prop], val) { return i } return nil } } guard let salaamI = places.firstIndex(withProperty: \.name, ==, "Dar Es Salaam") else { fatalError() } print("Dar Es Salaam has index: \(salaamI)") guard let lessThan5I = places.firstIndex(withProperty: \.population, <, 5) else { fatalError() } print("First city with less than 5mil population: \(places[lessThan5I].name)") guard let aI = places.firstIndex(withProperty: \.name, { $0.hasPrefix($1) }, "A") else { fatalError() } print("Population of first city starting with A: \(places[aI].population)")</lang>
Same as first method Tcl<lang Tcl># records is a list of dicts. set records { { name "Lagos" population 21.0 } { name "Cairo" population 15.2 } { name "Kinshasa-Brazzaville" population 11.3 } { name "Greater Johannesburg" population 7.55 } { name "Mogadishu" population 5.85 } { name "Khartoum-Omdurman" population 4.98 } { name "Dar Es Salaam" population 4.7 } { name "Alexandria" population 4.58 } { name "Abidjan" population 4.4 } { name "Casablanca" population 3.98 } }
proc search {records test action} { set index 0 foreach record $records { dict with record {} if $test $action incr index } error "No match found!" }
puts [search $records {$name eq "Dar Es Salaam"} {return $index}]
puts [search $records {$population < 5.0} {return $name}]
puts [search $records {[string match A* $name]} {return $population}] </lang>
6 Khartoum-Omdurman 4.58 Wren<lang ecmascript>import "/dynamic" for Tuple var Element = Tuple.create("Element", ["record", "index"]) var findFirst = Fn.new { |seq, pred| var i = 0 for (e in seq) { if (pred.call(e)) return Element.new(e, i) i = i + 1 } return Element.new(null, -1) } var City = Tuple.create("City", ["name", "pop"]) var cities = [ City.new("Lagos", 21.0), City.new("Cairo", 15.2), City.new("Kinshasa-Brazzaville", 11.3), City.new("Greater Johannesburg", 7.55), City.new("Mogadishu", 5.85), City.new("Khartoum-Omdurman", 4.98), City.new("Dar Es Salaam", 4.7), City.new("Alexandria", 4.58), City.new("Abidjan", 4.4), City.new("Casablanca", 3.98) ] var index = findFirst.call(cities) { |c| c.name == "Dar Es Salaam" }.index System.print("Index of the first city whose name is 'Dar Es Salaam' is %(index).") var city = findFirst.call(cities) { |c| c.pop < 5 }.record.name System.print("First city whose population is less than 5 million is %(city).") var pop = findFirst.call(cities) { |c| c.name[0] == "A" }.record.pop System.print("The population of the first city whose name begins with 'A' is %(pop).")</lang>
Index of the first city whose name is 'Dar Es Salaam' is 6. First city whose population is less than 5 million is Khartoum-Omdurman. The population of the first city whose name begins with 'A' is 4.58. zkl<lang zkl>list:=T(SD("name","Lagos", "population",21.0), // SD is a fixed dictionary SD("name","Cairo", "population",15.2), SD("name","Kinshasa-Brazzaville", "population",11.3), SD("name","Greater Johannesburg", "population", 7.55), SD("name","Mogadishu", "population", 5.85), SD("name","Khartoum-Omdurman", "population", 4.98), SD("name","Dar Es Salaam", "population", 4.7), SD("name","Alexandria", "population", 4.58), SD("name","Abidjan", "population", 4.4), SD("name","Casablanca", "population", 3.98)); // Test case 1: n:=list.filter1n(fcn(city){ city["name"]=="Dar Es Salaam" }); // one way n:=list.filter1n(fcn(city){ city["name"].matches("dar es salaam") }); // or this way n.println("==index of ",list[n].values); // Test case 2: city:=list.filter1(fcn(city){ city["population"]<5.0 }); // stop after first match city["name"].println(" is the first city with population under 5 million."); // Test case 3: city:=list.filter1(fcn(city){ city["name"][0]=="A" }); println("The first \"A*\" city (%s) with population under 5 million: %f".fmt(city.values.xplode()));</lang> where a SD is a small read only dictionary and filter1 is a filter that stops at the first match (returning the matched item). The filter method returns False on failure. The YAJL library could be used to parse the JSON data directly (eg if the data is from the web).
6==index of L("Dar Es Salaam",4.7) Khartoum-Omdurman is the first city with population under 5 million. The first "A*" city (Alexandria) with population under 5 million: 4.580000 |
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