Associative array/Creation: Difference between revisions
Content added Content deleted
m (→[[Ruby]]: Updated formatting. Added link to nil.) |
|||
Line 138: | Line 138: | ||
hash[777] # => 'unknown key 777' |
hash[777] # => 'unknown key 777' |
||
hash[666] # => 'devil' |
hash[666] # => 'devil' |
||
==[[OCaml]]== |
|||
A simple idiom to create a hash table mapping strings to integers: |
|||
let hash = Hashtbl.create 0;; |
|||
List.iter (fun (key, value) -> Hashtbl.add hash key value) |
|||
["foo", 5; "bar", 10; "baz", 15];; |
|||
To retrieve a value: |
|||
let bar = Hashtbl.find hash "bar";; (* bar = 5 *) |
|||
To retrieve a value, returning a default if the key is not found: |
|||
let quux = try Hashtbl.find hash "quux" with Not_found -> some_value;; |
Revision as of 21:33, 23 January 2007
![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.
In this task, the goal is to create an associative array.
C++
Compiler: g++ 4.0.2
#include <map> #include <string> #include <iostream> #include <ostream> int main() { // This is an associative array which maps strings to ints typedef std::map<std::string, int> colormap_t; colormap_t colormap; // First, populate it with some values colormap["red"] = 0xff0000; colormap["green"] = 0x00ff00; colormap["blue"] = 0x0000ff; colormap["my favourite color"] = 0x00ffff; // then, get some values out int color = colormap["green"]; // color gets 0x00ff00 color = colormap["black"]; // accessing unassigned values assigns them to 0 // get some value out without accidentally inserting new ones colormap_t::iterator i = colormap.find("green"); if (i == colormap.end()) { std::cerr << "color not found!\n"; } else { color = i->second; } // Now I changed my mind about my favourite color, so change it colormap["my favourite color"] = 0x337733; // print out all defined colors for (colormap_t::iterator i = colormap.begin(); i != colormap.end(); ++i) std::cerr << "colormap[\"" << i->first << "\"] = 0x" << std::hex << i->second << "\n"; }
Perl
Interpeter: Perl
Defining a Hash
# using => key does not need to be quoted unless it contains special chars my %hash = ( key1 => 'val1', 'key-2' => 2, three => -238.83, 4 => 'val3', ); # using , both key and value need to be quoted if containing something non-numeric in nature my %hash = ( 'key1', 'val1', 'key-2', 2, 'three', -238.83, 4, 'val3', );
Defining a HashRef
my $hashref = { key1 => 'val1', 'key-2' => 2, three => -238.83, 4 => 'val3', }
Using a Hash
print $hash{'key1'}; $hash{'key1'} = 'val1'; @hash{'key1', 'three'} = ('val1', -238.83);
Using a HashRef
print $hash->{'key1'}; $hash->{'key1'} = 'val1'; @hash->{'key1', 'three'} = ('val1', -238.83);
Python
In Python, hashes are called dictionaries.
# empty dictionary d = {} d['spam'] = 1 d['eggs'] = 2
# dictionaries with two keys d1 = {'spam': 1, 'eggs': 2} d2 = dict(spam=1, eggs=2)
# dictionaries from tuple list d1 = dict([('spam', 1), ('eggs', 2)]) d2 = dict(zip(['spam', 'eggs'], [1, 2]))
# iterating over keys for key in d: print key, d[key]
# iterating over (key, value) pairs for key, value in d.iteritems(): print key, value
Create a generic mapping function that applys a callback to elements in a list:
Ruby
A hash object that returns nil for unknown keys
hash={} hash[666]='devil' hash[777] # => nil hash[666] # => 'devil'
A hash object that returns 'unknown key' for unknown keys
hash=Hash.new('unknown key') hash[666]='devil' hash[777] # => 'unknown key' hash[666] # => 'devil'
A hash object that returns "unknown key #{key}" for unknown keys
hash=Hash.new{|h,k|h[k]="unknown key #{k}"} hash[666]='devil' hash[777] # => 'unknown key 777' hash[666] # => 'devil'
OCaml
A simple idiom to create a hash table mapping strings to integers:
let hash = Hashtbl.create 0;; List.iter (fun (key, value) -> Hashtbl.add hash key value) ["foo", 5; "bar", 10; "baz", 15];;
To retrieve a value:
let bar = Hashtbl.find hash "bar";; (* bar = 5 *)
To retrieve a value, returning a default if the key is not found:
let quux = try Hashtbl.find hash "quux" with Not_found -> some_value;;