Remove duplicate elements

Remove duplicate elements
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).

Ada

Works with: GNAT version GPL 2007

<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>

APL

Works with: Dyalog APL

The primitive monad ∪ means "unique", so: <lang apl>∪ 1 2 3 1 2 3 4 1 1 2 3 4</lang>

Works with: APL2

<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>

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>

C

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>

1. 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>

C++

This version uses std::set, which requires its element type be comparable using the < operator. <lang cpp>#include <set>

1. 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.

Works with: GCC

<lang cpp>#include <ext/hash_set>

1. 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.

Works with: GCC

<lang cpp>#include <tr1/unordered_set>

1. 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>

1. include <iterator>
2. 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>

C#

Works with: C# version 2+

<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>

Works with: C# version 3+

<lang csharp>int[] nums = {1, 1, 2, 3, 4, 4}; int[] unique = nums.Distinct().ToArray();</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>

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() {

   int[] data = [1, 2, 3, 2, 3, 4];
   int[int] hash;
   foreach(el; data)
       hash[el] = 0;

}</lang>

E

<lang e>[1,2,3,2,3,4].asSet().getElements()</lang>

Erlang

<lang erlang>List = [1, 2, 3, 2, 2, 4, 5, 5, 4, 6, 6, 5]. Set = sets:from_list(List).</lang>

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 } prune .

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

<lang forth>1 2 3 4 5 6 ok</lang>

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>

Go

<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, len(unique_set))
 i := 0
 for x := range unique_set {
   result[i] = x
   i++
 }
 return result

}

func main() {

 fmt.Println(uniq([]int {1,2,3,2,3,4})) // prints: [3 1 4 2]

}</lang> replace "int" with another type (must be boolean, numeric, string, pointer, function, interface, map, or channel type) to use for a list of another type

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 list.unique() assert list.size() == 8 println " Filtered List: ${list}"

list = [1, 2, 3, 'a', 'b', 'c', 2, 3, 4, 'b', 'c', 'd'] assert list.size() == 12

// Converting to Set def set = new HashSet(list) assert set.size() == 8 println " Set: ${set}"

// Converting to Order-preserving Set set = new LinkedHashSet(list) assert set.size() == 8 println "List-ordered 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]
             Set: [1, d, 2, 3, 4, b, c, a]
List-ordered Set: [1, 2, 3, a, b, c, 4, d]

Haskell

<lang haskell>values = [1,2,3,2,3,4] unique = List.nub values</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

Icon

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
->

Unicon

This Icon solution works in Unicon.

IDL

<lang idl>non_repeated_values = array[uniq(array, sort( array))]</lang>

J

<lang j> ] a=: 4 5 ?@$ 13 NB. 4 by 5 matrix of numbers chosen from 0 to 12 4 3 2 8 0 1 9 5 1 7 6 3 9 9 4 2 1 5 3 2

  , a     NB. sequence of the same elements

4 3 2 8 0 1 9 5 1 7 6 3 9 9 4 2 1 5 3 2

  ~. , a  NB. unique elements

4 3 2 8 0 1 9 5 7 6</lang> The verb ~. removes duplicate items from any array (numeric, character, or other; vector, matrix, rank-n array). For example: <lang j> ~. 'chthonic eleemosynary paronomasiac' chtoni elmsyarp</lang> Or

<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

Works with: Java version 1.5

<lang java5>import java.util.Set; import java.util.HashSet; import java.util.Arrays;

Object[] data = {1, 2, 3, "a", "b", "c", 2, 3, 4, "b", "c", "d"}; Set<Object> uniqueSet = new HashSet<Object>(Arrays.asList(data)); Object[] unique = uniqueSet.toArray();</lang>

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>

Logo

Works with: UCB 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

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>

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> Custom function (reordering of elements is possible): <lang Mathematica>NoDupes[input_List] := Split[Sort[input]]All, 1 NoDupes[{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>

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"

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>

Objective-C

<lang objc>NSArray *items = [NSArray arrayWithObjects:@"A", @"B", @"C", @"B", @"A", nil];

NSSet *unique = [NSSet setWithArray:items];</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>

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>

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>

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>

Perl

Library: List::MoreUtilsMoreUtils

(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

Works with: Rakudo version #23 "Lisbon"

<lang perl6>sub nub (@a) {

   my @b;
   none(@b) eqv $_ and push @b, $_ for @a;
   return @b;

}

my @unique = nub [1, 2, 3, 5, 2, 4, 3, -3, 7, 5, 6];</lang> Or just use the .uniq builtin.

<lang perl6>my @unique = [1, 2, 3, 5, 2, 4, 3, -3, 7, 5, 6].uniq;</lang>

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>

  declare t(20) fixed initial (1, 5, 6, 2, 1, 7,
     5, 22, 4, 19, 1, 1, 6, 6, 6, 8, 9, 10, 11, 12);
  declare (i, j, k, n, e) fixed;

  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, f(11));

</lang>

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>

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>

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>

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>

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>

See also http://www.peterbe.com/plog/uniqifiers-benchmark and http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560

R

<lang r>items <- c(1,2,3,2,4,3,2) unique (items)</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]

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>

Ruby

<lang ruby>ary = [1,1,2,1,'redundant',[1,2,3],[1,2,3],'redundant'] uniq_ary = ary.uniq

1. => [1, 2, "redundant", [1, 2, 3]]</lang>

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)</lang>

Scheme

<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 (list 1 2 1 3 2 4 5))</lang>

<lang scheme>(1 2 3 4 5)</lang>

Some implementations provide remove-duplicates in their standard library.

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>

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>|aCollection| "Example of creating a collection" a := #( 1 1 2 'hello' 'world' #symbol #another 2 'hello' #symbol ). a asSet printNl.</lang>

Output:

Set (1 2 #symbol 'world' #another 'hello' )

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>

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$ # 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 -u 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'

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>