Remove duplicate elements: Difference between revisions
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=={{header|FreeBASIC}}== |
=={{header|FreeBASIC}}== |
Revision as of 23:40, 15 January 2018
You are encouraged to solve this task according to the task description, using any language you may know.
Given an Array, derive a sequence of elements in which all duplicates are removed.
There are basically three approaches seen here:
- Put the elements into a hash table which does not allow duplicates. The complexity is O(n) on average, and O(n2) worst case. This approach requires a hash function for your type (which is compatible with equality), either built-in to your language, or provided by the user.
- Sort the elements and remove consecutive duplicate elements. The complexity of the best sorting algorithms is O(n log n). This approach requires that your type be "comparable", i.e., have an ordering. Putting the elements into a self-balancing binary search tree is a special case of sorting.
- Go through the list, and for each element, check the rest of the list to see if it appears again, and discard it if it does. The complexity is O(n2). The up-shot is that this always works on any type (provided that you can test for equality).
360 Assembly
<lang 360asm>* Remove duplicate elements - 18/10/2015 REMDUP CSECT
USING REMDUP,R15 set base register SR R6,R6 i=0 LA R8,1 k=1
LOOPK C R8,N do k=1 to n
BH ELOOPK LR R1,R8 k SLA R1,2 L R9,T-4(R1) e=t(k) LR R7,R8 k BCTR R7,0 j=k-1
LOOPJ C R7,=F'1' do j=k-1 to 1 by -1
BL ELOOPJ LR R1,R7 j SLA R1,2 L R2,T-4(R1) t(j) CR R9,R2 if e=t(j) then goto iter BE ITER BCTR R7,0 j=j-1 B LOOPJ
ELOOPJ LA R6,1(R6) i=i+1
LR R1,R6 i SLA R1,2 ST R9,T-4(R1) t(i)=e
ITER LA R8,1(R8) k=k+1
B LOOPK
ELOOPK LA R10,PG pgi=@pg
LA R8,1 k=1
LOOP CR R8,R6 do k=1 to i
BH ELOOP LR R1,R8 k SLA R1,2 L R2,T-4(R1) t(k) XDECO R2,PG+80 edit t(k) MVC 0(3,R10),PG+89 output t(k) on 3 char LA R10,3(R10) pgi=pgi+3 LA R8,1(R8) k=k+1 B LOOP
ELOOP XPRNT PG,80 print buffer
XR R15,R15 set return code BR R14 return to caller
T DC F'6',F'6',F'1',F'5',F'6',F'2',F'1',F'7',F'5',F'22'
DC F'4',F'19',F'1',F'1',F'6',F'8',F'9',F'10',F'11',F'12'
N DC A((N-T)/4) number of T items PG DC CL92' '
YREGS END REMDUP</lang>
- Output:
6 1 5 2 7 22 4 19 8 9 10 11 12
ACL2
<lang lisp>(remove-duplicates xs)</lang>
Ada
<lang ada>with Ada.Containers.Ordered_Sets; with Ada.Text_IO; use Ada.Text_IO;
procedure Unique_Set is
package Int_Sets is new Ada.Containers.Ordered_Sets(Integer); use Int_Sets; Nums : array (Natural range <>) of Integer := (1,2,3,4,5,5,6,7,1); Unique : Set; Set_Cur : Cursor; Success : Boolean;
begin
for I in Nums'range loop Unique.Insert(Nums(I), Set_Cur, Success); end loop; Set_Cur := Unique.First; loop Put_Line(Item => Integer'Image(Element(Set_Cur))); exit when Set_Cur = Unique.Last; Set_Cur := Next(Set_Cur); end loop;
end Unique_Set;</lang>
ALGOL 68
Using the associative array code from Associative_array/Iteration#ALGOL_68 <lang algol68># use the associative array in the Associate array/iteration task #
- this example uses strings - for other types, the associative #
- array modes AAELEMENT and AAKEY should be modified as required #
PR read "aArray.a68" PR
- returns the unique elements of list #
PROC remove duplicates = ( []STRING list )[]STRING:
BEGIN REF AARRAY elements := INIT LOC AARRAY; INT count := 0; FOR pos FROM LWB list TO UPB list DO IF NOT ( elements CONTAINSKEY list[ pos ] ) THEN # first occurance of this element # elements // list[ pos ] := ""; count +:= 1 FI OD; # construct an array of the unique elements from the # # associative array - the new list will not necessarily be # # in the original order # [ count ]STRING result; REF AAELEMENT e := FIRST elements; FOR pos WHILE e ISNT nil element DO result[ pos ] := key OF e; e := NEXT elements OD; result END; # remove duplicates #
- test the duplicate removal #
print( ( remove duplicates( ( "A", "B", "D", "A", "C", "F", "F", "A" ) ), newline ) ) </lang>
APL
The primitive monad ∪ means "unique", so: <lang apl>∪ 1 2 3 1 2 3 4 1 1 2 3 4</lang>
<lang apl>w←1 2 3 1 2 3 4 1
((⍳⍨w)=⍳⍴w)/w
1 2 3 4</lang>
AppleScript
<lang applescript>unique({1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d"})
on unique(x)
set R to {} repeat with i in x if i is not in R then set end of R to i's contents end repeat return R
end unique</lang>
Or, more generally, we can allow for customised definitions of equality and duplication, by following the Haskell prelude in defining a nub :: [a] -> [a] function which is a special case of nubBy :: (a -> a -> Bool) -> [a] -> [a]
In the following example, equality is defined as case-insensitive for strings. We would obtain a different list of unique strings by adjusting the Eq :: a -> a -> Bool function to make it consider case.
<lang AppleScript>-- CASE-INSENSITIVE UNIQUE ELEMENTS ------------------------------------------
-- nub :: [a] -> [a] on nub(xs)
-- Eq :: a -> a -> Bool script Eq on |λ|(x, y) ignoring case x = y end ignoring end |λ| end script nubBy(Eq, xs)
end nub
-- TEST ----------------------------------------------------------------------
on run
{intercalate(space, ¬ nub(splitOn(space, "4 3 2 8 0 1 9 5 1 7 6 3 9 9 4 2 1 5 3 2"))), ¬ intercalate("", ¬ nub(characters of "abcabc ABCABC"))} --> {"4 3 2 8 0 1 9 5 7 6", "abc "}
end run
-- GENERIC FUNCTIONS ---------------------------------------------------------
-- filter :: (a -> Bool) -> [a] -> [a] on filter(f, xs)
tell mReturn(f) set lst to {} set lng to length of xs repeat with i from 1 to lng set v to item i of xs if |λ|(v, i, xs) then set end of lst to v end repeat return lst end tell
end filter
-- intercalate :: Text -> [Text] -> Text on intercalate(strText, lstText)
set {dlm, my text item delimiters} to {my text item delimiters, strText} set strJoined to lstText as text set my text item delimiters to dlm return strJoined
end intercalate
-- 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 |λ| : f end script end if
end mReturn
-- nubBy :: (a -> a -> Bool) -> [a] -> [a] on nubBy(fnEq, xxs)
set lng to length of xxs if lng > 1 then set x to item 1 of xxs set xs to items 2 thru -1 of xxs set p to mReturn(fnEq) -- notEq :: a -> Bool script notEq on |λ|(a) not (p's |λ|(a, x)) end |λ| end script {x} & nubBy(fnEq, filter(notEq, xs)) else xxs end if
end nubBy
-- splitOn :: Text -> Text -> [Text] on splitOn(strDelim, strMain)
set {dlm, my text item delimiters} to {my text item delimiters, strDelim} set lstParts to text items of strMain set my text item delimiters to dlm return lstParts
end splitOn</lang>
- Output:
<lang AppleScript>{"4 3 2 8 0 1 9 5 7 6", "abc "}</lang>
Applesoft BASIC
<lang basic>100 DIM L$(15) 110 L$(0) = "NOW" 120 L$(1) = "IS" 130 L$(2) = "THE" 140 L$(3) = "TIME" 150 L$(4) = "FOR" 160 L$(5) = "ALL" 170 L$(6) = "GOOD" 180 L$(7) = "MEN" 190 L$(8) = "TO" 200 L$(9) = "COME" 210 L$(10) = "TO" 220 L$(11) = "THE" 230 L$(12) = "AID" 240 L$(13) = "OF" 250 L$(14) = "THE" 260 L$(15) = "PARTY."
300 N = 15 310 GOSUB 400 320 FOR I = 0 TO N 330 PRINT L$(I) " " ; 340 NEXT 350 PRINT 360 END
400 REMREMOVE DUPLICATES 410 FOR I = N TO 1 STEP -1 420 I$ = L$(I) 430 FOR J = 0 TO I - 1 440 EQ = I$ = L$(J) 450 IF NOT EQ THEN NEXT J 460 IF EQ THEN GOSUB 500 470 NEXT I 480 RETURN
500 REMREMOVE ELEMENT 510 L$(I) = L$(N) 520 L$(N) = "" 530 N = N - 1 540 RETURN</lang>
AutoHotkey
Built in Sort has an option to remove duplicates <lang AutoHotkey>a = 1,2,1,4,5,2,15,1,3,4 Sort, a, a, NUD`, MsgBox % a ; 1,2,3,4,5,15</lang>
AWK
We produce an array a with duplicates from a string; then index a second array b with the contents of a, so that duplicates make only one entry; then produce a string with the keys of b, which is finally output. <lang awk>$ awk 'BEGIN{split("a b c d c b a",a);for(i in a)b[a[i]]=1;r="";for(i in b)r=r" "i;print r}' a b c d</lang>
BBC BASIC
<lang bbcbasic> DIM list$(15)
list$() = "Now", "is", "the", "time", "for", "all", "good", "men", \ \ "to", "come", "to", "the", "aid", "of", "the", "party." num% = FNremoveduplicates(list$()) FOR i% = 0 TO num%-1 PRINT list$(i%) " " ; NEXT PRINT END DEF FNremoveduplicates(l$()) LOCAL i%, j%, n%, i$ n% = 1 FOR i% = 1 TO DIM(l$(), 1) i$ = l$(i%) FOR j% = 0 TO i%-1 IF i$ = l$(j%) EXIT FOR NEXT IF j%>=i% l$(n%) = i$ : n% += 1 NEXT = n%</lang>
- Output:
Now is the time for all good men to come aid of party.
Bracmat
Here are three solutions. The first one (A) uses a hash table, the second (B) uses a pattern for spotting the elements that have a copy further on in the list and only adds those elements to the answer that don't have copies further on. The third solution (C) utilises an mechanism that is very typical of Bracmat, namely that sums (and also products) always are transformed to a normalised form upon evaluation. Normalisation means that terms are ordered in a unique way and that terms that are equal, apart from a numerical factor, are replaced by a single term with a numerical factor that is the sum of the numerical factors of each term. The answer is obtained by replacing all numerical factors by 1
as the last step.
The list contains atoms and also a few non-atomic expressions. The hash table needs atomic keys, so we apply the str
function when searching and inserting elements.
<lang bracmat>2 3 5 7 11 13 17 19 cats 222 (-100.2) "+11" (1.1) "+7" (7.) 7 5 5 3 2 0 (4.4) 2:?LIST
(A=
( Hashing = h elm list . new$hash:?h & whl ' ( !arg:%?elm ?arg & ( (h..find)$str$!elm | (h..insert)$(str$!elm.!elm) ) ) & :?list & (h..forall) $ ( = .!arg:(?.?arg)&!arg !list:?list ) & !list )
& put$("Solution A:" Hashing$!LIST \n,LIN) );
(B=
( backtracking = answr elm . :?answr & !arg : ? ( %?`elm ? ( !elm ? | &!answr !elm:?answr ) & ~ ) | !answr )
& put$("Solution B:" backtracking$!LIST \n,LIN) );
(C=
( summing = sum car LIST . !arg:?LIST & 0:?sum & whl ' ( !LIST:%?car ?LIST & (.!car)+!sum:?sum ) & whl ' ( !sum:#*(.?el)+?sum & !el !LIST:?LIST ) & !LIST )
& put$("Solution C:" summing$!LIST \n,LIN) );
( !A & !B & !C & )</lang> Only solution B produces a list with the same order of elements as in the input.
Solution A: 19 (4.4) 17 11 13 (1.1) (7.) 222 +11 7 5 3 2 0 cats (-100.2) +7 Solution B: 11 13 17 19 cats 222 (-100.2) +11 (1.1) +7 (7.) 7 5 3 0 (4.4) 2 Solution C: (7.) (4.4) (1.1) (-100.2) cats 222 19 17 13 11 7 5 3 2 0 +7 +11
Brat
<lang brat>some_array = [1 1 2 1 'redundant' [1 2 3] [1 2 3] 'redundant']
unique_array = some_array.unique</lang>
C
O(n^2) version, using linked lists
Since there's no way to know ahead of time how large the new data structure will need to be, we'll return a linked list instead of an array.
<lang c>#include <stdio.h>
- include <stdlib.h>
struct list_node {int x; struct list_node *next;}; typedef struct list_node node;
node * uniq(int *a, unsigned alen)
{if (alen == 0) return NULL; node *start = malloc(sizeof(node)); if (start == NULL) exit(EXIT_FAILURE); start->x = a[0]; start->next = NULL;
for (int i = 1 ; i < alen ; ++i) {node *n = start; for (;; n = n->next) {if (a[i] == n->x) break; if (n->next == NULL) {n->next = malloc(sizeof(node)); n = n->next; if (n == NULL) exit(EXIT_FAILURE); n->x = a[i]; n->next = NULL; break;}}}
return start;}
int main(void)
{int a[] = {1, 2, 1, 4, 5, 2, 15, 1, 3, 4}; for (node *n = uniq(a, 10) ; n != NULL ; n = n->next) printf("%d ", n->x); puts(""); return 0;}</lang>
- Output:
1 2 4 5 15 3
O(n^2) version, pure arrays
<lang c>#include <stdio.h>
- include <stdlib.h>
- include <stdbool.h>
- include <string.h>
/* Returns `true' if element `e' is in array `a'. Otherwise, returns `false'.
* Checks only the first `n' elements. Pure, O(n). */
bool elem(int *a, size_t n, int e) {
for (size_t i = 0; i < n; ++i) if (a[i] == e) return true;
return false;
}
/* Removes the duplicates in array `a' of given length `n'. Returns the number
* of unique elements. In-place, order preserving, O(n ^ 2). */
size_t nub(int *a, size_t n) {
size_t m = 0;
for (size_t i = 0; i < n; ++i) if (!elem(a, m, a[i])) a[m++] = a[i];
return m;
}
/* Out-place version of `nub'. Pure, order preserving, alloc < n * sizeof(int)
* bytes, O(n ^ 2). */
size_t nub_new(int **b, int *a, size_t n) {
int *c = malloc(n * sizeof(int)); memcpy(c, a, n * sizeof(int)); int m = nub(c, n); *b = malloc(m * sizeof(int)); memcpy(*b, c, m * sizeof(int)); free(c); return m;
}
int main(void) {
int a[] = {1, 2, 1, 4, 5, 2, 15, 1, 3, 4}; int *b;
size_t n = nub_new(&b, a, sizeof(a) / sizeof(a[0]));
for (size_t i = 0; i < n; ++i) printf("%d ", b[i]); puts("");
free(b); return 0;
}</lang>
- Output:
1 2 4 5 15 3
Sorting method
Using qsort and return uniques in-place:<lang c>#include <stdio.h>
- include <stdlib.h>
int icmp(const void *a, const void *b) {
- define _I(x) *(const int*)x
return _I(a) < _I(b) ? -1 : _I(a) > _I(b);
- undef _I
}
/* filter items in place and return number of uniques. if a separate
list is desired, duplicate it before calling this function */
int uniq(int *a, int len) { int i, j; qsort(a, len, sizeof(int), icmp); for (i = j = 0; i < len; i++) if (a[i] != a[j]) a[++j] = a[i]; return j + 1; }
int main() { int x[] = {1, 2, 1, 4, 5, 2, 15, 1, 3, 4}; int i, len = uniq(x, sizeof(x) / sizeof(x[0])); for (i = 0; i < len; i++) printf("%d\n", x[i]);
return 0; }</lang>
- Output:
1 2 3 4 5 15
C#
<lang csharp>int[] nums = { 1, 1, 2, 3, 4, 4 }; List<int> unique = new List<int>(); foreach (int n in nums)
if (!unique.Contains(n)) unique.Add(n);</lang>
<lang csharp>int[] nums = {1, 1, 2, 3, 4, 4}; int[] unique = nums.Distinct().ToArray();</lang>
C++
This version uses std::set, which requires its element type be comparable using the < operator. <lang cpp>#include <set>
- include <iostream>
using namespace std;
int main() {
typedef set<int> TySet; int data[] = {1, 2, 3, 2, 3, 4};
TySet unique_set(data, data + 6);
cout << "Set items:" << endl; for (TySet::iterator iter = unique_set.begin(); iter != unique_set.end(); iter++) cout << *iter << " "; cout << endl;
}</lang>
This version uses hash_set, which is part of the SGI extension to the Standard Template Library. It is not part of the C++ standard library. It requires that its element type have a hash function.
<lang cpp>#include <ext/hash_set>
- include <iostream>
using namespace std;
int main() {
typedef __gnu_cxx::hash_set<int> TyHash; int data[] = {1, 2, 3, 2, 3, 4};
TyHash unique_set(data, data + 6);
cout << "Set items:" << endl; for (TyHash::iterator iter = unique_set.begin(); iter != unique_set.end(); iter++) cout << *iter << " "; cout << endl;
}</lang>
This version uses unordered_set, which is part of the TR1, which is likely to be included in the next version of C++. It is not part of the C++ standard library. It requires that its element type have a hash function.
<lang cpp>#include <tr1/unordered_set>
- include <iostream>
using namespace std;
int main() {
typedef tr1::unordered_set<int> TyHash; int data[] = {1, 2, 3, 2, 3, 4};
TyHash unique_set(data, data + 6);
cout << "Set items:" << endl; for (TyHash::iterator iter = unique_set.begin(); iter != unique_set.end(); iter++) cout << *iter << " "; cout << endl;
}</lang>
Alternative method working directly on the array:
<lang cpp>#include <iostream>
- include <iterator>
- include <algorithm>
// helper template template<typename T> T* end(T (&array)[size]) { return array+size; }
int main() {
int data[] = { 1, 2, 3, 2, 3, 4 }; std::sort(data, end(data)); int* new_end = std::unique(data, end(data)); std::copy(data, new_end, std::ostream_iterator<int>(std::cout, " "); std::cout << std::endl;
}</lang>
Using sort, unique, and erase on a vector.
<lang cpp>#include <algorithm>
- include <iostream>
- include <vector>
int main() {
std::vector<int> data = {1, 2, 3, 2, 3, 4};
std::sort(data.begin(), data.end()); data.erase(std::unique(data.begin(), data.end()), data.end());
for(int& i: data) std::cout << i << " "; std::cout << std::endl; return 0;
}</lang>
CafeOBJ
<lang CafeOBJ> -- The parametrized module NO-DUP-LIST(ELEMENTS :: TRIV) defines the signature of simple Haskell like list structure. -- The removal of duplicates is handled by the equational properties listed after the signature in brackets {} -- The binary operation _,_ is associative, commutative, and idempotent. -- This list structure does not permit duplicates, they are removed during evaluation (called reduction in CafeOBJ) -- Actual code is contained in module called NO-DUP-LIST. -- The tests are performed after opening instantiated NO-DUP-LIST with various concrete types. -- For further details see: http://www.ldl.jaist.ac.jp/cafeobj/ mod! NO-DUP-LIST(ELEMENTS :: TRIV) {
[ List < Elem < Elt] -- Sorts in Ordered Sorted Algebra op [] : -> List { prec: 0 } -- Empty List op _,_ : Elt Elt -> Elt { comm assoc idem prec: 80 l-assoc } op [_] : Elt -> List { prec: 0 }
}
-- Test on lists of INT, CHARACTER, and STRING open NO-DUP-LIST(INT) reduce [ 1 , 2 , 1 , 1 ] . -- Gives [ 1 , 2 ] open NO-DUP-LIST(CHARACTER) reduce [ 'a' , 'b' , 'a' , 'a' ] . -- Gives [ 'a' , 'b' ] open NO-DUP-LIST(STRING) reduce [ "abc" , "def" , "abc" ] . -- Gives [ "def" , "abc" ] </lang>
Ceylon
<lang ceylon><String|Integer>[] data = [1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d"]; <String|Integer>[] unique = HashSet { *data }.sequence();</lang>
Clojure
<lang lisp>user=> (distinct [1 3 2 9 1 2 3 8 8 1 0 2]) (1 3 2 9 8 0) user=></lang>
CoffeeScript
<lang coffeescript>data = [ 1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d" ] set = [] set.push i for i in data when not (i in set)
console.log data console.log set</lang>
- Output:
[ 1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd' ] [ 1, 2, 3, 'a', 'b', 'c', 4, 'd' ]
Common Lisp
To remove duplicates non-destructively:
<lang lisp>(remove-duplicates '(1 3 2 9 1 2 3 8 8 1 0 2)) > (9 3 8 1 0 2)</lang>
Or, to remove duplicates in-place:
<lang lisp>(delete-duplicates '(1 3 2 9 1 2 3 8 8 1 0 2)) > (9 3 8 1 0 2)</lang>
D
<lang d>void main() {
import std.stdio, std.algorithm;
[1, 3, 2, 9, 1, 2, 3, 8, 8, 1, 0, 2] .sort() .uniq .writeln;
}</lang>
- Output:
[0, 1, 2, 3, 8, 9]
Using an associative array: <lang d>void main() {
import std.stdio;
immutable data = [1, 3, 2, 9, 1, 2, 3, 8, 8, 1, 0, 2];
bool[int] hash; foreach (el; data) hash[el] = true; hash.byKey.writeln;
}</lang>
- Output:
[8, 0, 1, 9, 2, 3]
Like code D#1, but with an array returned: <lang d>void main() {
import std.stdio, std.algorithm, std.array;
auto a = [5,4,32,7,6,4,2,6,0,8,6,9].sort.uniq.array; a.writeln;
}</lang>
- Output:
[0, 2, 4, 5, 6, 7, 8, 9, 32]
Déjà Vu
<lang dejavu>} for item in [ 1 10 1 :hi :hello :hi :hi ]: @item !. keys set{</lang>
- Output:
[ 1 :hello 10 :hi ]
Delphi
Generics were added in Delphi2009.
<lang Delphi>program RemoveDuplicateElements;
{$APPTYPE CONSOLE}
uses Generics.Collections;
var
i: Integer; lIntegerList: TList<Integer>;
const
INT_ARRAY: array[1..7] of Integer = (1, 2, 2, 3, 4, 5, 5);
begin
lIntegerList := TList<Integer>.Create; try for i in INT_ARRAY do if not lIntegerList.Contains(i) then lIntegerList.Add(i);
for i in lIntegerList do Writeln(i); finally lIntegerList.Free; end;
end.</lang>
- Output:
1 2 3 4 5
E
<lang e>[1,2,3,2,3,4].asSet().getElements()</lang>
ECL
<lang ecl> inNumbers := DATASET([{1},{2},{3},{4},{1},{1},{7},{8},{9},{9},{0},{0},{3},{3},{3},{3},{3}], {INTEGER Field1}); DEDUP(SORT(inNumbers,Field1)); </lang>
- Output:
0 1 2 3 4 7 8 9
Elena
ELENA 3.3 : <lang elena>import extensions. import system'collections. import system'routines.
program = [
var nums := (1,1,2,3,4,4). dictionary unique := Dictionary new. nums forEach(:n)[ unique[n] := n ]. console printLine(unique).
].</lang>
- Output:
1,2,3,4
Elixir
Elixir has an Enum.uniq
built-in function.
<lang elixir>defmodule RC do
# Set approach def uniq1(list), do: MapSet.new(list) |> MapSet.to_list # Sort approach def uniq2(list), do: Enum.sort(list) |> Enum.dedup # Go through the list approach def uniq3(list), do: uniq3(list, []) defp uniq3([], res), do: Enum.reverse(res) defp uniq3([h|t], res) do if h in res, do: uniq3(t, res), else: uniq3(t, [h | res]) end
end
num = 10000 max = div(num, 10) list = for _ <- 1..num, do: :rand.uniform(max) funs = [&Enum.uniq/1, &RC.uniq1/1, &RC.uniq2/1, &RC.uniq3/1] Enum.each(funs, fn fun ->
result = fun.([1,1,2,1,'redundant',1.0,[1,2,3],[1,2,3],'redundant',1.0]) :timer.tc(fn -> Enum.each(1..100, fn _ -> fun.(list) end) end) |> fn{t,_} -> IO.puts "#{inspect fun}:\t#{t/1000000}\t#{inspect result}" end.()
end)</lang>
- Output:
&Enum.uniq/1: 0.296 [1, 2, 'redundant', 1.0, [1, 2, 3]] &RC.uniq1/1: 0.686 [1, 2, 1.0, [1, 2, 3], 'redundant'] &RC.uniq2/1: 0.921 [1, 1.0, 2, [1, 2, 3], 'redundant'] &RC.uniq3/1: 1.497 [1, 2, 'redundant', 1.0, [1, 2, 3]]
Erlang
<lang erlang>List = [1, 2, 3, 2, 2, 4, 5, 5, 4, 6, 6, 5]. UniqueList = gb_sets:to_list(gb_sets:from_list(List)). % Alternatively the builtin: Unique_list = lists:usort( List ). </lang>
Euphoria
<lang euphoria>include sort.e
function uniq(sequence s)
sequence out s = sort(s) out = s[1..1] for i = 2 to length(s) do if not equal(s[i],out[$]) then out = append(out, s[i]) end if end for return out
end function
constant s = {1, 2, 1, 4, 5, 2, 15, 1, 3, 4} ? s ? uniq(s)</lang>
- Output:
{1,2,1,4,5,2,15,1,3,4} {1,2,3,4,5,15}
F#
The simplest way is to build a set from the given array (this actually works for any enumerable input sequence type, not just arrays): <lang fsharp> set [|1;2;3;2;3;4|] </lang> gives: <lang fsharp> val it : Set<int> = seq [1; 2; 3; 4] </lang>
Factor
<lang factor>USING: sets ; V{ 1 2 1 3 2 4 5 } members .
V{ 1 2 3 4 5 }</lang>
Forth
Forth has no built-in hashtable facility, so the easiest way to achieve this goal is to take the "uniq" program as an example.
The word uniq, if given a sorted array of cells, will remove the duplicate entries and return the new length of the array. For simplicity, uniq has been written to process cells (which are to Forth what "int" is to C), but could easily be modified to handle a variety of data types through deferred procedures, etc.
The input data is assumed to be sorted.
<lang forth>\ Increments a2 until it no longer points to the same value as a1 \ a3 is the address beyond the data a2 is traversing.
- skip-dups ( a1 a2 a3 -- a1 a2+n )
dup rot ?do over @ i @ <> if drop i leave then cell +loop ;
\ Compress an array of cells by removing adjacent duplicates \ Returns the new count
- uniq ( a n -- n2 )
over >r \ Original addr to return stack cells over + >r \ "to" addr now on return stack, available as r@ dup begin ( write read ) dup r@ < while 2dup @ swap ! \ copy one cell cell+ r@ skip-dups cell 0 d+ \ increment write ptr only repeat r> 2drop r> - cell / ;</lang>
Here is another implementation of "uniq" that uses a popular parameters and local variables extension words. It is structurally the same as the above implementation, but uses less overt stack manipulation.
<lang forth>: uniqv { a n \ r e -- n }
a n cells+ to e a dup to r \ the write address lives on the stack begin r e < while r @ over ! r cell+ e skip-dups to r cell+ repeat a - cell / ;</lang>
To test this code, you can execute:
<lang forth>create test 1 , 2 , 3 , 2 , 6 , 4 , 5 , 3 , 6 , here test - cell / constant ntest
- .test ( n -- ) 0 ?do test i cells + ? loop ;
test ntest 2dup cell-sort uniq .test</lang>
- Output:
1 2 3 4 5 6 ok
Fortran
Fortran has no built-in hash functions or sorting functions but the code below implements the compare all elements algorithm.
<lang fortran>
program remove_dups
implicit none integer :: example(12) ! The input integer :: res(size(example)) ! The output integer :: k ! The number of unique elements integer :: i, j
example = [1, 2, 3, 2, 2, 4, 5, 5, 4, 6, 6, 5] k = 1 res(1) = example(1) outer: do i=2,size(example) do j=1,k if (res(j) == example(i)) then ! Found a match so start looking again cycle outer end if end do ! No match found so add it to the output k = k + 1 res(k) = example(i) end do outer write(*,advance='no',fmt='(a,i0,a)') 'Unique list has ',k,' elements: ' write(*,*) res(1:k)
end program remove_dups
</lang>
Same as above but using 'ANY' to check if the input number already exists in the array of unique elements:
<lang fortran> program remove_dups
implicit none integer :: example(12) ! The input integer :: res(size(example)) ! The output integer :: k ! The number of unique elements integer :: i
example = [1, 2, 3, 2, 2, 4, 5, 5, 4, 6, 6, 5] k = 1 res(1) = example(1) do i=2,size(example) ! if the number already exist in res check next if (any( res == example(i) )) cycle ! No match found so add it to the output k = k + 1 res(k) = example(i) end do
write(*,advance='no',fmt='(a,i0,a)') 'Unique list has ',k,' elements: ' write(*,*) res(1:k)
end program remove_dups
</lang>
- Output:
Unique list has 6 elements: 1 2 3 4 5 6
FreeBASIC
<lang freebasic>' FB 1.05.0 Win64
Sub removeDuplicates(a() As Integer, b() As Integer)
Dim lb As Integer = LBound(a) Dim ub As Integer = UBound(a) If ub = -1 Then Return empty array Redim b(lb To ub) b(lb) = a(lb) Dim count As Integer = 1 Dim unique As Boolean For i As Integer = lb + 1 To ub unique = True For j As Integer = lb to i - 1 If a(i) = a(j) Then unique = False Exit For End If Next j If unique Then b(lb + count) = a(i) count += 1 End If Next i
If count > 0 Then Redim Preserve b(lb To lb + count - 1)
End Sub
Dim a(1 To 10) As Integer = {1, 2, 1, 4, 5, 2, 15, 1, 3, 4} Dim b() As Integer removeDuplicates a(), b()
For i As Integer = LBound(b) To UBound(b)
Print b(i); " ";
Next
Print Print "Press any key to quit" Sleep</lang>
- Output:
1 2 4 5 15 3
Frink
The following demonstrates two of the simplest ways of removing duplicates. <lang frink> b = [1, 5, 2, 6, 6, 2, 2, 1, 9, 8, 6, 5]
// One way, using OrderedList. An OrderedList is a type of array that keeps // its elements in order. The items must be comparable. a = new OrderedList println[a.insertAllUnique[b]]
// Another way, using the "set" datatype and back to an array. println[toArray[toSet[b]] </lang>
- Output:
Note that sets are not guaranteed to be printed in any specific order.
[1, 2, 5, 6, 8, 9] [9, 8, 6, 5, 2, 1]
GAP
<lang gap># Built-in, using sets (which are also lists) a := [ 1, 2, 3, 1, [ 4 ], 5, 5, [4], 6 ];
- [ 1, 2, 3, 1, [ 4 ], 5, 5, [ 4 ], 6 ]
b := Set(a);
- [ 1, 2, 3, 5, 6, [ 4 ] ]
IsSet(b);
- true
IsList(b);
- true</lang>
Go
Map solution
<lang go>package main
import "fmt"
func uniq(list []int) []int { unique_set := make(map[int]bool, len(list)) for _, x := range list { unique_set[x] = true } result := make([]int, 0, len(unique_set)) for x := range unique_set { result = append(result, x) } return result }
func main() { fmt.Println(uniq([]int{1, 2, 3, 2, 3, 4})) // prints: [3 4 1 2] (but in a semi-random order) }</lang>
Map preserving order
It takes only small changes to the above code to preserver order. Just store the sequence in the map: <lang go>package main
import "fmt"
func uniq(list []int) []int { unique_set := make(map[int]int, len(list)) i := 0 for _, x := range list { if _, there := unique_set[x]; !there { unique_set[x] = i i++ } } result := make([]int, len(unique_set)) for x, i := range unique_set { result[i] = x } return result }
func main() { fmt.Println(uniq([]int{1, 2, 3, 2, 3, 4})) // prints: [1 2 3 4] }</lang>
Float64, removing duplicate NaNs
In solutions above, you just replace int
with another type to use for a list of another type. (See Associative_arrays/Creation#Go for acceptable types.) Except a weird thing happens with NaNs. They (correctly) don't compare equal, so you have to special case them if you want to remove duplicate NaNs:
<lang go>package main
import ( "fmt" "math" )
func uniq(list []float64) []float64 { unique_set := map[float64]int{} i := 0 nan := false for _, x := range list { if _, exists := unique_set[x]; exists { continue } if math.IsNaN(x) { if nan { continue } else { nan = true } } unique_set[x] = i i++ } result := make([]float64, len(unique_set)) for x, i := range unique_set { result[i] = x } return result }
func main() { fmt.Println(uniq([]float64{1, 2, math.NaN(), 2, math.NaN(), 4})) // Prints [1 2 NaN 4] }</lang>
Any type using reflection
Go doesn't have templates or generics, but it does have reflection. Using this it's possible to build a version that will work on almost any array or slice type. Using the reflect package for this does make the code less readable.
Normally in Go this type of solution is somewhat rare. Instead, for very short code (such as min, max, abs) it's common to cast or make a type specific function by hand as needed. For longer code, often an interface can be used instead (see the sort
package for an example).
Note: due to details with how Go handles map keys that contain a NaN somewhere (including within a complex or even within a sub struct field) this version simply omits any NaN containing values it comes across and returns a bool to indicate if that happened. This version is otherwise a translation of the above order preserving map implementation, it does not for example call reflect.DeepEqual so elements with pointers to distinct but equal values will be treated as non-equal. <lang go>package main
import ( "fmt" "math" "reflect" )
func uniq(x interface{}) (interface{}, bool) { v := reflect.ValueOf(x) if !v.IsValid() { panic("uniq: invalid argument") } if k := v.Kind(); k != reflect.Array && k != reflect.Slice { panic("uniq: argument must be an array or a slice") } elemType := v.Type().Elem() intType := reflect.TypeOf(int(0)) mapType := reflect.MapOf(elemType, intType) m := reflect.MakeMap(mapType) i := 0 for j := 0; j < v.Len(); j++ { x := v.Index(j) if m.MapIndex(x).IsValid() { continue } m.SetMapIndex(x, reflect.ValueOf(i)) if m.MapIndex(x).IsValid() { i++ } } sliceType := reflect.SliceOf(elemType) result := reflect.MakeSlice(sliceType, i, i) hadNaN := false for _, key := range m.MapKeys() { ival := m.MapIndex(key) if !ival.IsValid() { hadNaN = true } else { result.Index(int(ival.Int())).Set(key) } }
return result.Interface(), hadNaN }
type MyType struct { name string value float32 }
func main() { intArray := [...]int{5, 1, 2, 3, 2, 3, 4} intSlice := []int{5, 1, 2, 3, 2, 3, 4} stringSlice := []string{"five", "one", "two", "three", "two", "three", "four"} floats := []float64{1, 2, 2, 4, math.NaN(), 2, math.NaN(), math.Inf(1), math.Inf(1), math.Inf(-1), math.Inf(-1)} complexes := []complex128{1, 1i, 1 + 1i, 1 + 1i, complex(math.NaN(), 1), complex(1, math.NaN()), complex(math.Inf(+1), 1), complex(1, math.Inf(1)), complex(math.Inf(-1), 1), complex(1, math.Inf(1)), } structs := []MyType{ {"foo", 42}, {"foo", 2}, {"foo", 42}, {"bar", 42}, {"bar", 2}, {"fail", float32(math.NaN())}, }
fmt.Print("intArray: ", intArray, " → ") fmt.Println(uniq(intArray)) fmt.Print("intSlice: ", intSlice, " → ") fmt.Println(uniq(intSlice)) fmt.Print("stringSlice: ", stringSlice, " → ") fmt.Println(uniq(stringSlice)) fmt.Print("floats: ", floats, " → ") fmt.Println(uniq(floats)) fmt.Print("complexes: ", complexes, "\n → ") fmt.Println(uniq(complexes)) fmt.Print("structs: ", structs, " → ") fmt.Println(uniq(structs)) // Passing a non slice or array will compile put // then produce a run time panic: //a := 42 //uniq(a) //uniq(nil) }</lang>
- Output:
intArray: [5 1 2 3 2 3 4] → [5 1 2 3 4] false intSlice: [5 1 2 3 2 3 4] → [5 1 2 3 4] false stringSlice: [five one two three two three four] → [five one two three four] false floats: [1 2 2 4 NaN 2 NaN +Inf +Inf -Inf -Inf] → [1 2 4 +Inf -Inf] true complexes: [(1+0i) (0+1i) (1+1i) (1+1i) (NaN+1i) (1+NaNi) (+Inf+1i) (1+Infi) (-Inf+1i) (1+Infi)] → [(1+0i) (0+1i) (1+1i) (+Inf+1i) (1+Infi) (-Inf+1i)] true structs: [{foo 42} {foo 2} {foo 42} {bar 42} {bar 2} {fail NaN}] → [{foo 42} {foo 2} {bar 42} {bar 2}] true
Groovy
<lang groovy>def list = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] assert list.size() == 12 println " Original List: ${list}"
// Filtering the List (non-mutating) def list2 = list.unique(false) assert list2.size() == 8 assert list.size() == 12 println " Filtered List: ${list2}"
// Filtering the List (in place) list.unique() assert list.size() == 8 println " Original List, filtered: ${list}"
def list3 = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] assert list3.size() == 12
// Converting to Set def set = list as Set assert set.size() == 8 println " Set: ${set}"</lang>
- Output:
Original List: [1, 2, 3, a, b, c, 2, 3, 4, b, c, d] Filtered List: [1, 2, 3, a, b, c, 4, d] Original List, filtered: [1, 2, 3, a, b, c, 4, d] Set: [1, 2, 3, a, b, c, 4, d]
Haskell
Usage
<lang haskell> print $ unique [4, 5, 4, 2, 3, 3, 4]
[4,5,2,3]</lang>
Sorted result using Set
O(n ln(n)). Requires there is a partial ordering of elements.
<lang haskell>import qualified Data.Set as Set
unique :: Ord a => [a] -> [a] unique = Set.toList . Set.fromList</lang>
Unsorted result using Set
O(n ln(n)). Retains original order. Requires there is a partial ordering of elements.
<lang haskell>import Data.Set
unique :: Ord a => [a] -> [a] unique = loop empty
where loop s [] = [] loop s (x : xs) | member x s = loop s xs | otherwise = x : loop (insert x s) xs</lang>
Using filter
O(n^2). Retains original order. Only requires that elements can be compared for equality.
<lang haskell>import Data.List
unique :: Eq a => [a] -> [a] unique [] = [] unique (x : xs) = x : unique (filter (x /=) xs)</lang>
Standard Library
<lang haskell>import Data.List Data.List.nub :: Eq a => [a] -> [a] Data.List.Unique.unique :: Ord a => [a] -> [a]</lang>
HicEst
<lang hicest>REAL :: nums(12) CHARACTER :: workspace*100
nums = (1, 3, 2, 9, 1, 2, 3, 8, 8, 1, 0, 2) WRITE(Text=workspace) nums ! convert to string EDIT(Text=workspace, SortDelDbls=workspace) ! do the job for a string READ(Text=workspace, ItemS=individuals) nums ! convert to numeric
WRITE(ClipBoard) individuals, "individuals: ", nums ! 6 individuals: 0 1 2 3 8 9 0 0 0 0 0 0 </lang>
Icon and Unicon
This solution preserves the original order of the elements. <lang Icon>procedure main(args)
every write(!noDups(args))
end
procedure noDups(L)
every put(newL := [], notDup(set(),!L)) return newL
end
procedure notDup(cache, a)
if not member(cache, a) then { insert(cache, a) return a }
end</lang> A sample run is:
->noDups a b c d c a b e a b c d e ->
IDL
<lang idl>non_repeated_values = array[uniq(array, sort( array))]</lang>
Inform 7
<lang inform7>To decide which list of Ks is (L - list of values of kind K) without duplicates: let result be a list of Ks; repeat with X running through L: add X to result, if absent; decide on result.</lang>
J
The verb ~.
removes duplicate items from any array (numeric, character, or other; vector, matrix, rank-n array). For example:
<lang j> ~. 4 3 2 8 0 1 9 5 1 7 6 3 9 9 4 2 1 5 3 2
4 3 2 8 0 1 9 5 7 6
~. 'chthonic eleemosynary paronomasiac'
chtoni elmsyarp</lang> Or (since J defines an item of an n dimensional array as its n-1 dimensional sub arrays):
<lang j> 0 1 1 2 0 */0 1 2 0 0 0 0 1 2 0 1 2 0 2 4 0 0 0
~. 0 1 1 2 0 */0 1 2
0 0 0 0 1 2 0 2 4</lang>
Java
<lang java5>import java.util.*;
class Test {
public static void main(String[] args) {
Object[] data = {1, 1, 2, 2, 3, 3, 3, "a", "a", "b", "b", "c", "d"}; Set<Object> uniqueSet = new HashSet<Object>(Arrays.asList(data)); for (Object o : uniqueSet) System.out.printf("%s ", o); }
}</lang>
1 a 2 b 3 c d
<lang java>import java.util.*;
class Test {
public static void main(String[] args) {
Object[] data = {1, 1, 2, 2, 3, 3, 3, "a", "a", "b", "b", "c", "d"}; Arrays.stream(data).distinct().forEach((o) -> System.out.printf("%s ", o)); }
}</lang>
1 2 3 a b c d
JavaScript
This uses the ===
"strict equality" operator, which does no type conversions (4 == "4"
is true but 4 === "4"
is false)
<lang javascript>function unique(ary) {
// concat() with no args is a way to clone an array var u = ary.concat().sort(); for (var i = 1; i < u.length; ) { if (u[i-1] === u[i]) u.splice(i,1); else i++; } return u;
}
var ary = [1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d", "4"]; var uniq = unique(ary); for (var i = 0; i < uniq.length; i++)
print(uniq[i] + "\t" + typeof(uniq[i]));</lang>
1 - number 2 - number 3 - number 4 - number 4 - string a - string b - string c - string d - string
Or, extend the prototype for Array: <lang javascript>Array.prototype.unique = function() {
var u = this.concat().sort(); for (var i = 1; i < u.length; ) { if (u[i-1] === u[i]) u.splice(i,1); else i++; } return u;
} var uniq = [1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d"].unique();</lang>
With reduce and arrow functions (ES6): <lang javascript>Array.prototype.unique = function() {
return this.sort().reduce( (a,e) => e === a[a.length-1] ? a : (a.push(e), a), [] )
}</lang>
With sets and spread operator (ES6): <lang javascript>Array.prototype.unique = function() {
return [... new Set(this)]
}</lang>
If, however, the array is homogenous, or we wish to interpret it as such by using JavaScript's Abstract Equality comparison (as in '==', see http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3) then it proves significantly faster to use a hash table.
For example, in ES 5:
<lang JavaScript>function uniq(lst) {
var u = [], dct = {}, i = lst.length, v;
while (i--) { v = lst[i], dct[v] || ( dct[v] = u.push(v) ); } u.sort(); // optional return u;
}</lang>
Or, to allow for customised definitions of equality and duplication, we can follow the Haskell prelude in defining a nub :: [a] -> [a] function which is a special case of nubBy :: (a -> a -> Bool) -> [a] -> [a]
<lang JavaScript>(function () {
'use strict';
// nub :: [a] -> [a] function nub(xs) {
// Eq :: a -> a -> Bool function Eq(a, b) { return a === b; }
// nubBy :: (a -> a -> Bool) -> [a] -> [a] function nubBy(fnEq, xs) { var x = xs.length ? xs[0] : undefined;
return x !== undefined ? [x].concat( nubBy(fnEq, xs.slice(1) .filter(function (y) { return !fnEq(x, y); })) ) : []; }
return nubBy(Eq, xs); }
// TEST return [ nub('4 3 2 8 0 1 9 5 1 7 6 3 9 9 4 2 1 5 3 2'.split(' ')) .map(function (x) { return Number(x); }), nub('chthonic eleemosynary paronomasiac'.split()) .join() ]
})();</lang>
- Output:
[[4, 3, 2, 8, 0, 1, 9, 5, 7, 6], "chtoni elmsyarp"]
jq
If it is acceptable to alter the ordering of elements, then the builtin (fast) filter, unique, can be used. It can be used for arrays with elements of any JSON type and returns the distinct elements in sorted order. <lang jq>[4,3,2,1,1,2,3,4] | unique</lang>
If all but the first occurrence of each element should be deleted, then the following function could be used. It retains the advantage of imposing no restrictions on the types of elements in the array and for that reason is slightly more complex than would otherwise be required. <lang jq>def removeAllButFirst:
# The hash table functions all expect the hash table to be the input. # Is x in the hash table? def hashed(x): (x|tostring) as $value | .[$value] as $bucket | $bucket and (.[$value] | index([x]));
# Add x to the hash table: def add_hash(x): (x|tostring) as $value | .[$value] as $bucket | if $bucket and ($bucket | index([x])) then . else .[$value] += [x] end;
reduce .[] as $item ( [[], {}]; # [array, hash] if .[1] | hashed($item) then . else [ (.[0] + [$item]), (.[1] | add_hash($item)) ] end) | .[0];
</lang>
Julia
<lang julia>a = [1, 2, 3, 4, 1, 2, 3, 4] @show unique(a) Set(a)</lang>
- Output:
unique(a) = [1, 2, 3, 4] Set(a) = Set([4, 2, 3, 1])
K
(Inspired by the J version.)
<lang K> a:4 5#20?13 / create a random 4 x 5 matrix (12 7 12 4 3
6 3 7 4 7 3 8 3 1 2 2 12 6 4 1)
,/a / flatten to array
12 7 12 4 3 6 3 7 4 7 3 8 3 1 2 2 12 6 4 1
?,/a / distinct elements
12 7 4 3 6 8 1 2
?"chthonic eleemosynary paronomasiac"
"chtoni elmsyarp"
?("this";"that";"was";"that";"was";"this")
("this"
"that" "was") 0 1 1 2 0 *\: 0 1 2
(0 0 0
0 1 2 0 1 2 0 2 4 0 0 0)
?0 1 1 2 0 *\: 0 1 2
(0 0 0
0 1 2 0 2 4)</lang>
Kotlin
<lang scala>fun main(args: Array<String>) {
val data = listOf(1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d") val set = data.distinct()
println(data) println(set)
}</lang>
- Output:
[1, 2, 3, a, b, c, 2, 3, 4, b, c, d] [1, 2, 3, a, b, c, 4, d]
Lang5
<lang lang5>: dip swap '_ set execute _ ;
- remove-duplicates
[] swap do unique? length 0 == if break then loop drop ;
- unique?
0 extract swap "2dup in if drop else append then" dip ;
[1 2 6 3 6 4 5 6] remove-duplicates .</lang> Built-in function: <lang lang5>[1 2 6 3 6 4 5 6] 's distinct [1 2 6 3 6 4 5 6] 's dress dup union .</lang>
Lasso
<lang Lasso >local( x = array(3,4,8,1,8,1,4,5,6,8,9,6), y = array ) with n in #x where #y !>> #n do => { #y->insert(#n) } // result: array(3, 4, 8, 1, 5, 6, 9)</lang>
Liberty BASIC
LB has arrays, but here the elements are stored in a space-separated string. <lang lb> a$ =" 1 $23.19 2 elbow 3 2 Bork 4 3 elbow 2 $23.19 " print "Original set of elements = ["; a$; "]"
b$ =removeDuplicates$( a$) print "With duplicates removed = ["; b$; "]"
end
function removeDuplicates$( in$)
o$ =" " i =1 do term$ =word$( in$, i, " ") if instr( o$, " "; term$; " ") =0 and term$ <>" " then o$ =o$ +term$ +" " i =i +1 loop until term$ ="" removeDuplicates$ =o$
end function </lang>
Original set of elements = [ 1 $23.19 2 elbow 3 2 Bork 4 3 elbow 2 $23.19 ] With duplicates removed = [ 1 $23.19 2 elbow 3 Bork 4 ]
Logo
<lang logo>show remdup [1 2 3 a b c 2 3 4 b c d] ; [1 a 2 3 4 b c d]</lang>
Lua
<lang Lua>items = {1,2,3,4,1,2,3,4,"bird","cat","dog","dog","bird"} flags = {} io.write('Unique items are:') for i=1,#items do
if not flags[items[i]] then io.write(' ' .. items[i]) flags[items[i]] = true end
end io.write('\n')</lang>
- Output:
Unique items are: 1 2 3 4 bird cat dog
Lua doesn't accept Not-a-Number (NaN) and nil as table key, we can handle them like this (Lua 5.3): <lang Lua>local items = {1,2,3,4,1,2,3,4,0/0,nil,"bird","cat","dog","dog","bird",0/0}
function rmdup(t)
local r,dup,c,NaN = {},{},1,{} for i=1,#t do local e = t[i] local k = e~=e and NaN or e if k~=nil and not dup[k] then c, r[c], dup[k]= c+1, e, true end end return r
end
print(table.concat(rmdup(items),' '))</lang>
- Output:
1 2 3 4 nan bird cat dog
Maple
This is simplest with a list, which is an immutable array. <lang Maple>> L := [ 1, 2, 1, 2, 3, 3, 2, 1, "a", "b", "b", "a", "c", "b" ];
L := [1, 2, 1, 2, 3, 3, 2, 1, "a", "b", "b", "a", "c", "b"]
> [op]({op}(L));
[1, 2, 3, "a", "b", "c"]</lang>
That is idiomatic, but perhaps a bit cryptic; here is a more verbose equivalent: <lang Maple>> convert( convert( L, 'set' ), 'list' );
[1, 2, 3, "a", "b", "c"]</lang>
For an Array, which is mutable, the table solution works well in Maple. <lang Maple>> A := Array( L ): > for u in A do T[u] := 1 end: Array( [indices]( T, 'nolist' ) );
[1, 2, 3, "c", "a", "b"]</lang>
Note that the output (due to the Array() constructor) is in fact an Array.
Mathematica
Built-in function: <lang Mathematica>DeleteDuplicates[{0, 2, 1, 4, 2, 0, 3, 1, 1, 1, 0, 3}]</lang> gives back: <lang Mathematica>{0, 2, 1, 4, 3}</lang>
Delete duplicates and return sorted elements: <lang Mathematica> Union[{0, 2, 1, 4, 2, 0, 3, 1, 1, 1, 0, 3}]</lang>
- gives back
- :
<lang Mathematica>{0, 1, 2, 3, 4}</lang>
MATLAB
MATLAB has a built-in function, "unique(list)", which performs this task.
Sample Usage:
<lang MATLAB>>> unique([1 2 6 3 6 4 5 6])
ans =
1 2 3 4 5 6</lang>
NOTE: The unique function only works for vectors and not for true arrays.
Maxima
<lang maxima>unique([8, 9, 5, 2, 0, 7, 0, 0, 4, 2, 7, 3, 9, 6, 6, 2, 4, 7, 9, 8, 3, 8, 0, 3, 7, 0, 2, 7, 6, 0]); [0, 2, 3, 4, 5, 6, 7, 8, 9]</lang>
MAXScript
<lang maxscript>uniques = #(1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d") for i in uniques.count to 1 by -1 do (
id = findItem uniques uniques[i] if (id != i) do deleteItem uniques i
)</lang>
ML
mLite
A bit like option 3, except copying each element as encountered, and checking to see if it has already been encountered <lang ocaml>fun mem (x, []) = false
| (x eql a, a :: as) = true | (x, _ :: as) = mem (x, as)
fun remdup ([], uniq) = rev uniq | (h :: t, uniq) = if mem(h, uniq) then remdup (t, uniq) else remdup (t, h :: uniq) | L = remdup (L, [])
println ` implode ` remdup ` explode "the quick brown fox jumped over the lazy dog"; println ` remdup [1,2,3,4,4,3,2,1, "dog","cat","dog", 1.1, 2.2, 3.3, 1.1]; </lang>
- Output:
the quickbrownfxjmpdvlazyg [1, 2, 3, 4, dog, cat, 1.1, 2.2, 3.3]
MUMPS
We'll take advantage of the fact that an array can only have one index of any specific value. Sorting into canonical order is a side effect. If the indices are strings containing the separator string, they'll be split apart.
<lang MUMPS>REMDUPE(L,S)
;L is the input listing ;S is the separator between entries ;R is the list to be returned NEW Z,I,R FOR I=1:1:$LENGTH(L,S) SET Z($PIECE(L,S,I))="" ;Repack for return SET I="",R="" FOR SET I=$O(Z(I)) QUIT:I="" SET R=$SELECT($L(R)=0:I,1:R_S_I) KILL Z,I QUIT R</lang>
Example:
USER>W $$REMDUPE^ROSETTA("1,2,3,4,5,2,5,""HELLO"",42,""WORLD""",",") 1,2,3,4,5,42,"HELLO","WORLD"
Nemerle
<lang Nemerle>using System.Console;
module RemDups {
Main() : void { def nums = array[1, 4, 6, 3, 6, 2, 7, 2, 5, 2, 6, 8]; def unique = $[n | n in nums].RemoveDuplicates(); WriteLine(unique); }
}</lang>
NetRexx
This sample takes advantage of the NetRexx built-in Rexx object's indexed string capability (associative arrays). Rexx indexed strings act very like hash tables: <lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols nobinary
-- Note: Task requirement is to process "arrays". The following converts arrays into simple lists of words: -- Putting the resulting list back into an array is left as an exercise for the reader. a1 = [2, 3, 5, 7, 11, 13, 17, 19, 'cats', 222, -100.2, +11, 1.1, +7, '7.', 7, 5, 5, 3, 2, 0, 4.4, 2] a2 = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] a3 = ['Now', 'is', 'the', 'time', 'for', 'all', 'good', 'men', 'to', 'come', 'to', 'the', 'aid', 'of', 'the', 'party.'] x = 0 lists = x = x + 1; lists[0] = x; lists[x] = array2wordlist(a1) x = x + 1; lists[0] = x; lists[x] = array2wordlist(a2) x = x + 1; lists[0] = x; lists[x] = array2wordlist(a3)
loop ix = 1 to lists[0]
nodups_list = remove_dups(lists[ix]) say ix.right(4)':' lists[ix] say .right(4)':' nodups_list say end ix
return
-- ============================================================================= method remove_dups(list) public static
newlist = nodups = '0' loop w_ = 1 to list.words() ix = list.word(w_) nodups[ix] = nodups[ix] + 1 -- we can even collect a count of dups if we want end w_ loop k_ over nodups newlist = newlist k_ end k_
return newlist.space
-- ============================================================================= method array2wordlist(ra = Rexx[]) public static
wordlist = loop r_ over ra wordlist = wordlist r_ end r_
return wordlist.space
</lang>
- Output:
1: 2 3 5 7 11 13 17 19 cats 222 -100.2 11 1.1 7 7. 7 5 5 3 2 0 4.4 2 : 13 2 3 17 19 7. 4.4 5 222 7 -100.2 1.1 cats 0 11 2: 1 2 3 a b c 2 3 4 b c d : c 2 d 3 4 a b 1 3: Now is the time for all good men to come to the aid of the party. : Now aid for men to the party. come time of is all good
NewLISP
<lang NewLISP>(unique '(1 2 3 a b c 2 3 4 b c d))</lang>
Nial
<lang nial>uniques := [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] cull uniques =+-+-+-+-+-+-+-+-+ =|1|2|3|a|b|c|4|d| =+-+-+-+-+-+-+-+-+</lang>
Using strand form <lang nial>cull 1 1 2 2 3 3 =1 2 3</lang>
Nim
<lang nim>import sequtils, algorithm, intsets
- Go through the list, and for each element, check the rest of the list to see
- if it appears again,
var items = @[1, 2, 3, 2, 3, 4, 5, 6, 7] echo deduplicate(items) # O(n^2)
proc filterDup(xs): seq[int] =
result = @[xs[0]] var last = xs[0] for x in xs[1..xs.high]: if x != last: result.add(x) last = x
- Put the elements into a hash table which does not allow duplicates.
var s = initIntSet() for x in items:
s.incl(x)
echo s
- Sort the elements and remove consecutive duplicate elements.
sort(items, system.cmp[int]) # O(n log n) echo filterDup(items) # O(n)</lang>
Objeck
<lang objeck> use Structure;
bundle Default {
class Unique { function : Main(args : String[]) ~ Nil { nums := [1, 1, 2, 3, 4, 4]; unique := IntVector->New();
each(i : nums) { n := nums[i]; if(unique->Has(n) = false) { unique->AddBack(n); }; };
each(i : unique) { unique->Get(i)->PrintLine(); }; } }
} </lang>
Objective-C
<lang objc>NSArray *items = [NSArray arrayWithObjects:@"A", @"B", @"C", @"B", @"A", nil];
NSSet *unique = [NSSet setWithArray:items];</lang>
OCaml
<lang ocaml>let uniq lst =
let unique_set = Hashtbl.create (List.length lst) in List.iter (fun x -> Hashtbl.replace unique_set x ()) lst; Hashtbl.fold (fun x () xs -> x :: xs) unique_set []
let _ =
uniq [1;2;3;2;3;4]</lang>
Another solution (preserves order of first occurrence): <lang ocaml>let uniq lst =
let seen = Hashtbl.create (List.length lst) in List.filter (fun x -> let tmp = not (Hashtbl.mem seen x) in Hashtbl.replace seen x (); tmp) lst
let _ =
uniq [1;2;3;2;3;4]</lang>
Solution reversing list order : <lang ocaml>let uniq l =
let rec tail_uniq a l = match l with | [] -> a | hd::tl -> tail_uniq (hd::a) (List.filter (fun x -> x != hd) tl) in tail_uniq [] l</lang>
<lang ocaml>List.sort_uniq compare [1;2;3;2;3;4]</lang>
Octave
<lang octave> input=[1 2 6 4 2 32 5 5 4 3 3 5 1 2 32 4 4]; output=unique(input); </lang>
Oforth
The list is converted to a set to remove duplicate elements
- Output:
import: set [ 1, 2, 3, 1, 2, 4, 1, 3, 4, 5 ] asSet println [1, 2, 3, 4, 5]
ooRexx
<lang ooRexx>data = .array~of(1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d") uniqueData = .set~new~union(data)~makearray~sort
say "Unique elements are" say do item over uniqueData
say item
end</lang>
- Output:
Unique elements are 1 2 3 4 a b c d
Oz
The following solutions only works if the value type is allowed as a key in a dictionary.
<lang oz>declare
fun {Nub Xs} D = {Dictionary.new} in for X in Xs do D.X := unit end {Dictionary.keys D} end
in
{Show {Nub [1 2 1 3 5 4 3 4 4]}}</lang>
PARI/GP
Sort and remove duplicates. Other methods should be implemented as well. <lang parigp>rd(v)={
vecsort(v,,8)
};</lang>
Pascal
<lang pascal>Program RemoveDuplicates;
const
iArray: array[1..7] of integer = (1, 2, 2, 3, 4, 5, 5);
var
rArray: array[1..7] of integer; i, pos, last: integer; newNumber: boolean;
begin
rArray[1] := iArray[1]; last := 1; pos := 1; while pos < high(iArray) do begin inc(pos); newNumber := true; for i := low(rArray) to last do if iArray[pos] = rArray[i] then begin newNumber := false;
break;
end; if newNumber then begin inc(last); rArray[last] := iArray[pos]; end; end; for i := low(rArray) to last do writeln (rArray[i]);
end.</lang>
- Output:
% ./RemoveDuplicates 1 2 3 4 5
Perl
(this version even preserves the order of first appearance of each element) <lang perl>use List::MoreUtils qw(uniq);
my @uniq = uniq qw(1 2 3 a b c 2 3 4 b c d);</lang>
It is implemented like this: <lang perl>my %seen; my @uniq = grep {!$seen{$_}++} qw(1 2 3 a b c 2 3 4 b c d);</lang>
Note: the following two solutions convert elements to strings in the result, so if you give it references they will lose the ability to be dereferenced.
Alternately: <lang perl>my %hash = map { $_ => 1 } qw(1 2 3 a b c 2 3 4 b c d); my @uniq = keys %hash;</lang>
Alternately: <lang perl>my %seen; @seen{qw(1 2 3 a b c 2 3 4 b c d)} = (); my @uniq = keys %seen;</lang>
Perl 6
<lang perl6>my @unique = [1, 2, 3, 5, 2, 4, 3, -3, 7, 5, 6].unique;</lang> Or just make a set of it. <lang perl6>set(1,2,3,5,2,4,3,-3,7,5,6).list</lang>
Phix
Preserves order of first occurence. Applies to any data type. Should be pretty efficient, as the tagsort is O(n log n), then there are two O(n) loops. <lang Phix>sequence test
function alpha(integer i, integer j) integer res
res = compare(test[i],test[j]) if res=0 then res = compare(i,j) end if return res
end function
function unique(sequence s) sequence at, valid = repeat(1,length(s)) object last, this integer ai, nxt
test = s at = custom_sort(routine_id("alpha"),tagset(length(test))) last = test[at[1]] for i=2 to length(at) do ai = at[i] this = test[ai] valid[ai] = last!=this last = this end for
nxt = find(0,valid) if nxt then for i=nxt+1 to length(test) do if valid[i] then test[nxt] = test[i] nxt += 1 end if end for test = test[1..nxt-1] end if return test
end function
?join(unique(split("Now is the time for all good men to come to the aid of the party."))) ?unique({1, 2, 1, 4, 5, 2, 15, 1, 3, 4}) ?unique({1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d"}) ?unique({1,3,2,9,1,2,3,8,8,1,0,2}) ?unique("chthonic eleemosynary paronomasiac")</lang>
- Output:
"Now is the time for all good men to come aid of party." {1,2,4,5,15,3} {1,2,3,"a","b","c",4,"d"} {1,3,2,9,8,0} "chtoni elmsyarp"
PHP
<lang php>$list = array(1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'); $unique_list = array_unique($list);</lang>
PicoLisp
There is a built-in function <lang PicoLisp>(uniq (2 4 6 1 2 3 4 5 6 1 3 5))</lang>
- Output:
-> (2 4 6 1 3 5)
PL/I
<lang PL/I>*process mar(1,72); remdup: Proc options(main);
declare t(20) fixed initial (6, 6, 1, 5, 6, 2, 1, 7, 5, 22, 4, 19, 1, 1, 6, 8, 9, 10, 11, 12); declare (i, j, k, n, e) fixed;
put skip list ('Input:'); put edit ((t(k) do k = 1 to hbound(t))) (skip,20(f(3))); n = hbound(t,1); i = 0;
outer:
do k = 1 to n; e = t(k); do j = k-1 to 1 by -1; if e = t(j) then iterate outer; end; i = i + 1; t(i) = e; end;
put skip list ('Unique elements are:'); put edit ((t(k) do k = 1 to i)) (skip,20(f(3)));
end;</lang>
- Output:
Input: 6 6 1 5 6 2 1 7 5 22 4 19 1 1 6 8 9 10 11 12 Unique elements are: 6 1 5 2 7 22 4 19 8 9 10 11 12
Pop11
<lang pop11>;;; Initial array lvars ar = {1 2 3 2 3 4};
- Create a hash table
lvars ht= newmapping([], 50, 0, true);
- Put all array as keys into the hash table
lvars i; for i from 1 to length(ar) do
1 -> ht(ar(i))
endfor;
- Collect keys into a list
lvars ls = []; appdata(ht, procedure(x); cons(front(x), ls) -> ls; endprocedure);</lang>
PostScript
<lang postscript>
[10 8 8 98 32 2 4 5 10 ] dup length dict begin aload let* currentdict {pop} map end
</lang>
PowerShell
The common array for both approaches: <lang powershell>$data = 1,2,3,1,2,3,4,1</lang> Using a hash table to remove duplicates: <lang powershell>$h = @{} foreach ($x in $data) {
$h[$x] = 1
}
$h.Keys</lang>
Sorting and removing duplicates along the way can be done with the Sort-Object
cmdlet.
<lang powershell>$data | Sort-Object -Unique</lang>
Removing duplicates without sorting can be done with the Select-Object
cmdlet.
<lang powershell>$data | Select-Object -Unique</lang>
Prolog
<lang prolog>uniq(Data,Uniques) :- sort(Data,Uniques).</lang>
Example usage: <lang prolog>?- uniq([1, 2, 3, 2, 3, 4],Xs). Xs = [1, 2, 3, 4]</lang>
Because sort/2 is GNU prolog and not ISO here is an ISO compliant version:
<lang prolog>member1(X,[H|_]) :- X==H,!.
member1(X,[_|T]) :- member1(X,T).
distinct([],[]). distinct([H|T],C) :- member1(H,T),!, distinct(T,C). distinct([H|T],[H|C]) :- distinct(T,C).</lang>
Example usage: <lang prolog>?- distinct([A, A, 1, 2, 3, 2, 3, 4],Xs). Xs = [A, 1, 2, 3, 4]</lang>
PureBasic
Task solved with the built in Hash Table which are called Maps in PureBasic <lang PureBasic>NewMap MyElements.s()
For i=0 To 9 ;Mark 10 items at random, causing high risk of duplication items.
x=Random(9) t$="Number "+str(x)+" is marked" MyElements(str(x))=t$ ; Add element 'X' to the hash list or overwrite if already included.
Next
ForEach MyElements()
Debug MyElements()
Next</lang> Output may look like this, e.g. duplicated items are automatically removed as they have the same hash value.
Number 0 is marked Number 2 is marked Number 5 is marked Number 6 is marked
Python
If all the elements are hashable (this excludes list, dict, set, and other mutable types), we can use a set: <lang python>items = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] unique = list(set(items))</lang>
or if we want to keep the order of the elements
<lang python>items = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] unique = [] helperset = set() for x in items:
if x not in helperset: unique.append(x) helperset.add(x)</lang>
If all the elements are comparable (i.e. <, >=, etc. operators; this works for list, dict, etc. but not for complex and many other types, including most user-defined types), we can sort and group: <lang python>import itertools items = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] unique = [k for k,g in itertools.groupby(sorted(items))]</lang>
If both of the above fails, we have to use the brute-force method, which is inefficient: <lang python>items = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] unique = [] for x in items:
if x not in unique: unique.append(x)</lang>
another way of removing duplicate elements from a list, while preserving the order would be to use OrderedDict module like so
<lang python>
from collections import OrderedDict as od
print(list(od.fromkeys([1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd']).keys())) </lang>
See also http://www.peterbe.com/plog/uniqifiers-benchmark and http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560
Qi
<lang qi> (define remove-duplicates
[] -> [] [A|R] -> (remove-duplicates R) where (element? A R) [A|R] -> [A|(remove-duplicates R)])
(remove-duplicates [a b a a b b c d e]) </lang>
R
<lang r>items <- c(1,2,3,2,4,3,2) unique (items)</lang>
Racket
Using the built-in function <lang Racket> -> (remove-duplicates '(2 1 3 2.0 a 4 5 b 4 3 a 7 1 3 x 2)) '(2 1 3 2.0 a 4 5 b 7 x) </lang>
Using a hash-table: <lang Racket> (define (unique/hash lst)
(hash-keys (for/hash ([x (in-list lst)]) (values x #t))))
</lang>
Using a set: <lang Racket> (define unique/set (compose1 set->list list->set)) </lang>
A definition that works with arbitrary sequences and allows specification of an equality predicate.
<lang Racket> (define (unique seq #:same-test [same? equal?])
(for/fold ([res '()]) ([x seq] #:unless (memf (curry same? x) res)) (cons x res)))
</lang>
-> (unique '(2 1 3 2.0 a 4 5 b 4 3 a 7 1 3 x 2)) '(1 2 3 a b x 4 5 7 2.0) -> (unique '(2 1 3 2.0 4 5 4.0 3 7 1 3 2) #:same-test =) '(7 5 4 3 1 2) -> (unique #(2 1 3 2.0 4 5 4.0 3 7 1 3 2)) '(7 5 4 3 1 2) -> (apply string (unique "absbabsbdbfbd")) "fdsba"
Raven
<lang raven>[ 1 2 3 'a' 'b' 'c' 2 3 4 'b' 'c' 'd' ] as items items copy unique print
list (8 items)
0 => 1 1 => 2 2 => 3 3 => "a" 4 => "b" 5 => "c" 6 => 4 7 => "d"</lang>
REBOL
<lang REBOL>print mold unique [1 $23.19 2 elbow 3 2 Bork 4 3 elbow 2 $23.19]</lang>
- Output:
[1 $23.19 2 elbow 3 Bork 4]
Red
<lang Red>>> items: [1 "a" "c" 1 3 4 5 "c" 3 4 5] >> unique items == [1 "a" "c" 3 4 5]</lang>
REXX
Note that in REXX, strings are quite literal.
- +7 is different from 7 (but compares numerically equal).
- 00 is different from 0 (but compares numerically equal).
- ─0 is different from 0 (but compares numerically equal).
- 7. is different from 7 (but compares numerically equal).
- Ab is different from AB (but can compare equal if made case insensitive).
Note that all the REXX examples below don't care what type of element is used, integer, floating point, character, binary, ···
version 1, using method 1
<lang rexx>/*REXX program removes any duplicate elements (items) that are in a list (using a hash).*/ $= '2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 2' /*item list.*/ say 'original list:' $ say right( words($), 17, '─') 'words in the original list.' z=; @.= /*initialize the NEW list & index list.*/
do j=1 for words($); y=word($,j) /*process the words (items) in the list*/ if @.y== then z=z y; @.y=. /*Not duplicated? Add to Z list,@ array*/ end /*j*/
say say 'modified list:' space(z) say right( words(z), 17, '─') 'words in the modified list.'
/*stick a fork in it, we're all done. */</lang>
- output when using the default input list:
original list: 2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 ──────────────23 words in the original list. modified list: 2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 0 4.4 ──────────────17 words in the modified list.
version 2, using a modified method 3
Instead of discard an element if it's a duplicated, it just doesn't add it to the new list.
Sorting of the list elements isn't necessary. <lang rexx>/*REXX program removes any duplicate elements (items) that are in a list (using a list).*/ $= '2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 2' /*item list.*/ say 'original list:' $ say right( words($), 17, '─') 'words in the original list.'
- =words($) /*process all the words in the list. */
do j=# by -1 for #; y=word($, j) /*get right-to-Left. */ _=wordpos(y, $, j + 1); if _\==0 then $=delword($,_,1) /*Dup? Then delete it*/ end /*j*/
say say 'modified list:' space($) say right( words(z), 17, '─') 'words in the modified list.'
/*stick a fork in it, we're all done. */</lang>
- output is identical to the 1st REXX version.
version 3, using method 3
<lang rexx>/*REXX program removes any duplicate elements (items) that are in a list (using 2 lists)*/ old = '2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 2' say 'original list:' old say right( words(old), 17, '─') 'words in the original list.' new= /*start with a clean (list) slate. */
do j=1 for words(old); _=word(old, j) /*process the words in the OLD list. */ if wordpos(_,new)==0 then new=new _ /*Doesn't exist? Then add word to NEW.*/ end /*j*/
say say 'modified list:' space(new) say right( words(new), 17, '─') 'words in the modified list.'
/*stick a fork in it, we're all done. */</lang>
- output is identical to the 1st REXX version.
version 4, using method 1 (hash table) via REXX stems
<lang rexx>/* REXX ************************************************************
- 26.11.2012 Walter Pachl
- added: show multiple occurrences
- /
old='2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5',
'3 2 0 4.4 2'
say 'old list='old say 'words in the old list=' words(old) new= found.=0 count.=0 Do While old<>
Parse Var old w old If found.w=0 Then Do new=new w found.w=1 End count.w=count.w+1 End
say 'new list='strip(new) say 'words in the new list=' words(new) Say 'Multiple occurrences:' Say 'occ word' Do While new<>
Parse Var new w new If count.w>1 Then Say right(count.w,3) w End</lang>
- Output:
old list=2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 2 words in the old list= 23 new list=2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 0 4.4 words in the new list= 17 Multiple occurrences: occ word 3 2 2 3 3 5 2 7
Ring
<lang ring> list = ["Now", "is", "the", "time", "for", "all", "good", "men", "to", "come", "to", "the", "aid", "of", "the", "party."] for i = 1 to len(list)
for j = i + 1 to len(list) if list[i] = list[j] del(list, j) j-- ok next
next
for n = 1 to len(list)
see list[n] + " "
next see nl </lang> Output:
Now is the time for all good men to come aid of party.
Ruby
Ruby has an Array#uniq
built-in method, which returns a new array by removing duplicate values in self.
<lang ruby>ary = [1,1,2,1,'redundant',[1,2,3],[1,2,3],'redundant']
p ary.uniq # => [1, 2, "redundant", [1, 2, 3]]</lang>
You can also write your own uniq method. <lang ruby>class Array
# used Hash def uniq1 each_with_object({}) {|elem, h| h[elem] = true}.keys end # sort (requires comparable) def uniq2 sorted = sort pre = sorted.first sorted.each_with_object([pre]){|elem, uniq| uniq << (pre = elem) if elem != pre} end # go through the list def uniq3 each_with_object([]) {|elem, uniq| uniq << elem unless uniq.include?(elem)} end
end
ary = [1,1,2,1,'redundant',[1,2,3],[1,2,3],'redundant'] p ary.uniq1 #=> [1, 2, "redundant", [1, 2, 3]] p ary.uniq2 rescue nil # Error (not comparable) p ary.uniq3 #=> [1, 2, "redundant", [1, 2, 3]]
ary = [1,2,3,7,6,5,2,3,4,5,6,1,1,1] p ary.uniq1 #=> [1, 2, 3, 7, 6, 5, 4] p ary.uniq2 #=> [1, 2, 3, 4, 5, 6, 7] p ary.uniq3 #=> [1, 2, 3, 7, 6, 5, 4]</lang>
A version without implementing class declarations: <lang ruby>def unique(array)
pure = Array.new for i in array flag = false for j in pure flag = true if j==i end pure << i unless flag end return pure
end
unique ["hi","hey","hello","hi","hey","heyo"] # => ["hi", "hey", "hello", "heyo"] unique [1,2,3,4,1,2,3,5,1,2,3,4,5] # => [1,2,3,4,5]</lang>
Run BASIC
<lang runbasic>a$ = "2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 2"
for i = 1 to len(a$)
a1$ = word$(a$,i) if a1$ = "" then exit for for i1 = 1 to len(b$) if a1$ = word$(b$,i1) then [nextWord] next i1 b$ = b$ + a1$ + " "
[nextWord] next i
print "Dups:";a$ print "No Dups:";b$</lang>
Dups:2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 7 5 5 3 2 0 4.4 2 No Dups:2 3 5 7 11 13 17 19 cats 222 -100.2 +11 1.1 +7 7. 0 4.4
Rust
<lang rust>use std::collections::HashSet; use std::hash::Hash;
fn remove_duplicate_elements_hashing<T: Hash + Eq>(elements: &mut Vec<T>) {
let set: HashSet<_> = elements.drain(..).collect(); elements.extend(set.into_iter());
}
fn remove_duplicate_elements_sorting<T: Ord>(elements: &mut Vec<T>) {
elements.sort_unstable(); // order does not matter elements.dedup();
}
fn main() {
let mut sample_elements = vec![0, 0, 1, 1, 2, 3, 2]; println!("Before removal of duplicates : {:?}", sample_elements); remove_duplicate_elements_sorting(&mut sample_elements); println!("After removal of duplicates : {:?}", sample_elements);
}</lang>
- Output:
Before removal of duplicates : [0, 0, 1, 1, 2, 3, 2] After removal of duplicates : [1, 0, 3, 2]
Scala
<lang scala>val list = List(1,2,3,4,2,3,4,99) val l2 = list.distinct // l2: scala.List[scala.Int] = List(1,2,3,4,99)
val arr = Array(1,2,3,4,2,3,4,99) val arr2 = arr.distinct // arr2: Array[Int] = Array(1, 2, 3, 4, 99) </lang>
Scheme
<lang scheme>(define (remove-duplicates l)
(cond ((null? l) '()) ((member (car l) (cdr l)) (remove-duplicates (cdr l))) (else (cons (car l) (remove-duplicates (cdr l))))))
(remove-duplicates '(1 2 1 3 2 4 5))</lang>
<lang scheme>(1 3 2 4 5)</lang>
Alternative approach: <lang scheme>(define (remove-duplicates l)
(do ((a '() (if (member (car l) a) a (cons (car l) a))) (l l (cdr l))) ((null? l) (reverse a))))
(remove-duplicates '(1 2 1 3 2 4 5))</lang>
<lang scheme>(1 2 3 4 5)</lang>
The function 'delete-duplicates' is also available in srfi-1.
Seed7
<lang seed7>$ include "seed7_05.s7i";
const proc: main is func
local const array integer: data is [] (1, 3, 2, 9, 1, 2, 3, 8, 8, 1, 0, 2); var set of integer: dataSet is (set of integer).value; var integer: number is 0; begin for number range data do incl(dataSet, number); end for; writeln(dataSet); end func;</lang>
- Output:
{0, 1, 2, 3, 8, 9}
SETL
<lang SETL>items := [0,7,6,6,4,9,7,1,2,3,2]; print(unique(items));</lang> Output in arbitrary order (convert tuple->set then set->tuple): <lang SETL>proc unique(items);
return [item: item in {item: item in items}];
end proc;</lang>
Preserving source order <lang SETL>proc unique(items);
seen := {}; return [item: item in items, nps in {#seen} | #(seen with:= item) > nps];
end proc;</lang>
<lang SETL>proc unique(items);
seen := {}; return [item: item in items, nps in {#seen} | #(seen with:= item) > nps];
end proc;</lang> <lang SETL>items := [0,7,6,6,4,9,7,1,2,3,2]; print(unique(items));</lang> Output in arbitrary order (convert tuple->set then set->tuple): <lang SETL>proc unique(items);
return [item: item in {item: item in items}];
end proc;</lang>
SETL4
<lang SETL4> set = new('set')
- Add all the elements of the array to the set.
add(set,array) </lang>
Sidef
<lang ruby>var ary = [1,1,2,1,'redundant',[1,2,3],[1,2,3],'redundant']; say ary.uniq.dump; say ary.last_uniq.dump;</lang>
- Output:
[1, 2, 'redundant', [1, 2, 3]] [2, 1, [1, 2, 3], 'redundant']
Slate
<lang slate>[|:s| #(1 2 3 4 1 2 3 4) >> s] writingAs: Set.
"==> {"Set traitsWindow" 1. 2. 3. 4}"</lang>
Smalltalk
<lang smalltalk>"Example of creating a collection" |a| a := #( 1 1 2 'hello' 'world' #symbol #another 2 'hello' #symbol ). a asSet.</lang>
- Output:
Set (1 2 #symbol 'world' #another 'hello' )
the above has the disadvantage of loosing the original order (because Sets are unordered, and the hashing shuffles elements into an arbitrary order). When tried, I got:
Set('world' 1 #another 'hello' #symbol 2)
on my system. This can be avoided by using an ordered set (which has also O(n) complexity) as below:
<lang smalltalk>|a| a := #( 1 1 2 'hello' 'world' #symbol #another 2 'hello' #symbol ). a asOrderedSet.</lang>
- Output:
OrderedSet(1 2 'hello' 'world' #symbol #another)
Sparkling
<lang sparkling>function undupe(arr) { var t = {}; foreach(arr, function(key, val) { t[val] = true; });
var r = {}; foreach(t, function(key) { r[sizeof r] = key; });
return r; }</lang>
Stata
Duplicates in a dataset
Stata can report duplicate lines, or remove them. See duplicates in Stata help.
<lang stata>. clear all . input x y 1 1 1 1 1 2 2 1 2 2 1 1 2 1 2 1 1 2 2 2 end
. duplicates drop x y, force . list
+-------+ | x y | |-------| 1. | 1 1 | 2. | 1 2 | 3. | 2 1 | 4. | 2 2 | +-------+</lang>
Mata
The uniqrows function removes duplicate rows from a matrix.
<lang stata>. mata
- a=1,1\1,1\1,2\2,1\2,2\1,1\2,1\2,1\1,2\2,2
- a
1 2 +---------+ 1 | 1 1 | 2 | 1 1 | 3 | 1 2 | 4 | 2 1 | 5 | 2 2 | 6 | 1 1 | 7 | 2 1 | 8 | 2 1 | 9 | 1 2 | 10 | 2 2 | +---------+
- uniqrows(a)
1 2 +---------+ 1 | 1 1 | 2 | 1 2 | 3 | 2 1 | 4 | 2 2 | +---------+</lang>
Swift
Requires elements to be hashable:
<lang swift>println(Array(Set([3,2,1,2,3,4])))</lang>
- Output:
[2, 3, 1, 4]
Another solution (preserves order of first occurrence). Also requires elements to be hashable:
<lang swift>func uniq<T: Hashable>(lst: [T]) -> [T] {
var seen = Set<T>(minimumCapacity: lst.count) return lst.filter { x in let unseen = !seen.contains(x) seen.insert(x) return unseen }
}
println(uniq([3,2,1,2,3,4]))</lang>
- Output:
[3, 2, 1, 4]
Only requires elements to be equatable, but runs in O(n^2): <lang swift>func uniq<T: Equatable>(lst: [T]) -> [T] {
var seen = [T]() return lst.filter { x in let unseen = find(seen, x) == nil if (unseen) { seen.append(x) } return unseen }
}
println(uniq([3,2,1,2,3,4]))</lang>
- Output:
[3, 2, 1, 4]
Tcl
The concept of an "array" in Tcl is strictly associative - and since there cannot be duplicate keys, there cannot be a redundant element in an array.
What is called "array" in many other languages is probably better represented by the "list" in Tcl (as in LISP).
With the correct option, the lsort
command will remove duplicates.
<lang tcl>set result [lsort -unique $listname]</lang>
TUSCRIPT
<lang tuscript> $$ MODE TUSCRIPT list_old="b'A'A'5'1'2'3'2'3'4" list_sort=MIXED_SORT (list_old) list_new=REDUCE (list_sort) PRINT list_old PRINT list_new </lang>
- Output:
(sorted)
b'A'A'5'1'2'3'2'3'4 1'2'3'4'5'A'b
or <lang tuscript> $$ MODE TUSCRIPT list_old="b'A'A'5'1'2'3'2'3'4" DICT list CREATE LOOP l=list_old DICT list LOOKUP l,num IF (num==0) DICT list ADD l ENDLOOP DICT list unload list list_new=JOIN (list) PRINT list_old PRINT list_new </lang>
- Output:
b'A'A'5'1'2'3'2'3'4 b'A'5'1'2'3'4
UnixPipes
Assuming a sequence is represented by lines in a file. <lang bash>bash$ # original list bash$ printf '6\n2\n3\n6\n4\n2\n' 6 2 3 6 4 2 bash$ # made uniq bash$ printf '6\n2\n3\n6\n4\n2\n'|sort -n|uniq 2 3 4 6 bash$</lang>
or
<lang bash>bash$ # made uniq bash$ printf '6\n2\n3\n6\n4\n2\n'|sort -nu 2 3 4 6 bash$</lang>
Ursala
The algorithm is to partition the list by equality and take one representative from each class, which can be done by letting the built in partition operator, |=, use its default comparison relation. This works on lists of any type including character strings but the comparison is based only on structural equivalence. It's up to the programmer to decide whether that's a relevant criterion for equivalence or else specify a better one. <lang Ursala>#cast %s
example = |=hS& 'mississippi'</lang>
- Output:
'mspi'
VBScript
Hash Table Approach <lang vb> Function remove_duplicates(list) arr = Split(list,",") Set dict = CreateObject("Scripting.Dictionary") For i = 0 To UBound(arr) If dict.Exists(arr(i)) = False Then dict.Add arr(i),"" End If Next For Each key In dict.Keys tmp = tmp & key & "," Next remove_duplicates = Left(tmp,Len(tmp)-1) End Function
WScript.Echo remove_duplicates("a,a,b,b,c,d,e,d,f,f,f,g,h") </lang>
- Output:
a,b,c,d,e,f,g,h
Vedit macro language
The input "array" is an edit buffer where each line is one element. <lang vedit>Sort(0, File_Size) // sort the data While(Replace("^(.*)\N\1$", "\1", REGEXP+BEGIN+NOERR)){} // remove duplicates</lang>
Vim Script
<lang vim>call filter(list, 'count(list, v:val) == 1')</lang>
Wart
<lang python>def (dedup l)
let exists (table) collect+each x l unless exists.x yield x exists.x <- 1</lang>
- Output:
dedup '(1 3 2 9 1 2 3 8 8 1 0 2) => (1 3 2 9 8 0)
Visual FoxPro
<lang vfp> LOCAL i As Integer, n As Integer, lcOut As String CLOSE DATABASES ALL CLEAR CREATE CURSOR nums (num I) INDEX ON num TAG num COLLATE "Machine" SET ORDER TO 0 n = 50 RAND(-1) FOR i = 1 TO n
INSERT INTO nums VALUES (RanInt(1, 10))
ENDFOR SELECT num, COUNT(num) As cnt FROM nums ; GROUP BY num INTO CURSOR grouped LIST OFF TO FILE grouped.txt NOCONSOLE lcOut = "" SCAN
lcOut = lcOut + TRANSFORM(num) + ","
ENDSCAN lcOut = LEFT(lcOut, LEN(lcOut)-1) ? lcOut
FUNCTION RanInt(tnLow As Integer, tnHigh As Integer) As Integer RETURN INT((tnHigh - tnLow + 1)*RAND() + tnLow) ENDFUNC </lang>
- Output:
NUM COUNT 1 6 2 5 3 6 4 8 5 4 6 3 7 8 8 7 9 3 Unique Values: 1,2,3,4,5,6,7,8,9
Wortel
<lang wortel>@uniq [1 2 3 2 1 2 3] ; returns [1 2 3]</lang>
XPL0
<lang XPL0>code Text=12; \built-in routine to display a string of characters string 0; \use zero-terminated strings (not MSb terminated)
func StrLen(S); \Return number of characters in an ASCIIZ string char S; int I; for I:= 0, -1>>1-1 do \(limit = 2,147,483,646 if 32 bit, or 32766 if 16 bit)
if S(I) = 0 then return I;
func Unique(S); \Remove duplicate bytes from string char S; int I, J, K, L; [L:= StrLen(S); \string length for I:= 0 to L-1 do \for all characters in string...
for J:= I+1 to L-1 do \scan rest of string for duplicates if S(I) = S(J) then \if duplicate then [for K:= J+1 to L do \ shift rest of string down (including S(K-1):= S(K); \ terminating zero) L:= L-1 \ string is now one character shorter ];
return S; \return pointer to string ];
Text(0, Unique("Pack my box with five dozen liquor jugs."))</lang>
- Output:
Pack myboxwithfvedznlqurjgs.
zkl
Using built ins: <lang zkl>zkl: Utils.Helpers.listUnique(T(1,3,2,9,1,2,3,8,8,"8",1,0,2,"8")) L(1,3,2,9,8,"8",0) zkl: "1,3,2,9,1,2,3,8,8,1,0,2".unique() ,012389</lang> Where listUnique is brute force: <lang zkl>fcn listUnique(xs){
xs.reduce(fcn(us,s){us.holds(s) and us or us.append(s)},L()) }</lang>
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