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Idiom #119 Deduplicate list

Remove duplicates from list x.
Explain if original order is preserved.

Illustration
import java.util.HashSet;
import java.util.Iterator;
final HashSet<T> seen = new HashSet<T>();
final Iterator<T> listIt = x.iterator();
while (listIt.hasNext()) {
  final T curr = listIt.next();
  if (seen.contains(curr)) {
    listIt.remove();
  } else {
    seen.add(curr);
  }
}
import java.util.HashSet;
import java.util.ArrayList;
x = new ArrayList<T>(new HashSet<T>(x));
import java.util.HashSet;
import java.util.List;
import java.util.Set;
Set<T> uniques = new HashSet<>(x);
x.clear();
x.addAll(uniques);
using System.Collections.Generic;
using System.Linq;
var uniques = x.Distinct().ToList();
import std.algorithm;
import std.array;
x = x.sort.uniq.array;
import std.container;
import std.array;
x = redBlackTree(x)[].array;
y := make(map[T]struct{}, len(x))
for _, v := range x {
	y[v] = struct{}{}
}
x2 := make([]T, 0, len(y))
for _, v := range x {
	if _, ok := y[v]; ok {
		x2 = append(x2, v)
		delete(y, v)
	}
}
x = x2
seen := make(map[T]bool)
j := 0
for _, v := range x {
	if !seen[v] {
		x[j] = v
		j++
		seen[v] = true
	}
}
x = x[:j]
seen := make(map[T]bool)
j := 0
for _, v := range x {
	if !seen[v] {
		x[j] = v
		j++
		seen[v] = true
	}
}
for i := j; i < len(x); i++ {
	x[i] = nil
}
x = x[:j]
import Data.List (sort)
nub (sort x)
$x = array_unique($x);
uses classes;
var
  list: TList;
begin
  for i:= list.count-1 downto 0 do
    if list.indexOf(list.items[i]) <> -1 then
      list.delete(i);
end;
use List::MoreUtils 'uniq';
@x = uniq(@x);
x = list(set(x))
x.uniq!
x.sort();
x.dedup();
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Idiom created by

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Related idioms

final HashSet<T> seen = new HashSet<T>();
final Iterator<T> listIt = x.iterator();
while (listIt.hasNext()) {
  final T curr = listIt.next();
  if (seen.contains(curr)) {
    listIt.remove();
  } else {
    seen.add(curr);
  }
}
x = new ArrayList<T>(new HashSet<T>(x));
Set<T> uniques = new HashSet<>(x);
x.clear();
x.addAll(uniques);
var uniques = x.Distinct().ToList();
x = x.sort.uniq.array;
x = redBlackTree(x)[].array;
y := make(map[T]struct{}, len(x))
for _, v := range x {
	y[v] = struct{}{}
}
x2 := make([]T, 0, len(y))
for _, v := range x {
	if _, ok := y[v]; ok {
		x2 = append(x2, v)
		delete(y, v)
	}
}
x = x2
seen := make(map[T]bool)
j := 0
for _, v := range x {
	if !seen[v] {
		x[j] = v
		j++
		seen[v] = true
	}
}
x = x[:j]
seen := make(map[T]bool)
j := 0
for _, v := range x {
	if !seen[v] {
		x[j] = v
		j++
		seen[v] = true
	}
}
for i := j; i < len(x); i++ {
	x[i] = nil
}
x = x[:j]
nub (sort x)
$x = array_unique($x);
var
  list: TList;
begin
  for i:= list.count-1 downto 0 do
    if list.indexOf(list.items[i]) <> -1 then
      list.delete(i);
end;
@x = uniq(@x);
x = list(set(x))
x.uniq!
x.sort();
x.dedup();