SymfonyWorld Online 2022 Winter Edition

array_unique

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

array_uniqueRemoves duplicate values from an array

Description

array_unique(array $array, int $flags = SORT_STRING): array

Takes an input array and returns a new array without duplicate values.

Note that keys are preserved. If multiple elements compare equal under the given flags, then the key and value of the first equal element will be retained.

Note: Two elements are considered equal if and only if (string) $elem1 === (string) $elem2 i.e. when the string representation is the same, the first element will be used.

Parameters

array

The input array.

flags

The optional second parameter flags may be used to modify the sorting behavior using these values:

Sorting type flags:

  • SORT_REGULAR - compare items normally (don't change types)
  • SORT_NUMERIC - compare items numerically
  • SORT_STRING - compare items as strings
  • SORT_LOCALE_STRING - compare items as strings, based on the current locale.

Return Values

Returns the filtered array.

Changelog

Version Description
7.2.0 If flags is SORT_STRING, formerly array has been copied and non-unique elements have been removed (without packing the array afterwards), but now a new array is built by adding the unique elements. This can result in different numeric indexes.

Examples

Example #1 array_unique() example

<?php
$input 
= array("a" => "green""red""b" => "green""blue""red");
$result array_unique($input);
print_r($result);
?>

The above example will output:

Array
(
    [a] => green
    [0] => red
    [1] => blue
)

Example #2 array_unique() and types

<?php
$input 
= array(4"4""3"43"3");
$result array_unique($input);
var_dump($result);
?>

The above example will output:

array(2) {
  [0] => int(4)
  [2] => string(1) "3"
}

Notes

Note: Note that array_unique() is not intended to work on multi dimensional arrays.

See Also

add a note

User Contributed Notes 28 notes

up
279
Ghanshyam Katriya(anshkatriya at gmail)
7 years ago
Create multidimensional array unique for any single key index.
e.g I want to create multi dimentional unique array for specific code

Code :
My array is like this,

<?php
$details
= array(
   
0 => array("id"=>"1", "name"=>"Mike",    "num"=>"9876543210"),
   
1 => array("id"=>"2", "name"=>"Carissa", "num"=>"08548596258"),
   
2 => array("id"=>"1", "name"=>"Mathew""num"=>"784581254"),
);
?>

You can make it unique for any field like id, name or num.

I have develop this function for same :
<?php
function unique_multidim_array($array, $key) {
   
$temp_array = array();
   
$i = 0;
   
$key_array = array();
   
    foreach(
$array as $val) {
        if (!
in_array($val[$key], $key_array)) {
           
$key_array[$i] = $val[$key];
           
$temp_array[$i] = $val;
        }
       
$i++;
    }
    return
$temp_array;
}
?>

Now, call this function anywhere from your code,

something like this,
<?php
$details
= unique_multidim_array($details,'id');
?>

Output will be like this :
<?php
$details
= array(
   
0 => array("id"=>"1","name"=>"Mike","num"=>"9876543210"),
   
1 => array("id"=>"2","name"=>"Carissa","num"=>"08548596258"),
);
?>
up
13
falundir at gmail dot com
4 years ago
I find it odd that there is no version of this function which allows you to use a comparator callable in order to determine items equality (like array_udiff and array_uintersect). So, here's my version for you:

<?php
function array_uunique(array $array, callable $comparator): array {
   
$unique_array = [];
    do {
       
$element = array_shift($array);
       
$unique_array[] = $element;

       
$array = array_udiff(
           
$array,
            [
$element],
           
$comparator
       
);
    } while (
count($array) > 0);

    return
$unique_array;
}
?>

And here is a test code:

<?php
class Foo {

    public
$a;

    public function
__construct(int $a) {
       
$this->a = $a;
    }
}

$array_of_objects = [new Foo(2), new Foo(1), new Foo(3), new Foo(2), new Foo(2), new Foo(1)];

$comparator = function (Foo $foo1, Foo $foo2): int {
    return
$foo1->a <=> $foo2->a;
};

var_dump(array_uunique($array_of_objects, $comparator)); // should output [Foo(2), Foo(1), Foo(3)]
?>
up
17
stoff@
5 years ago
In reply to performance tests array_unique vs foreach.

In PHP7 there were significant changes to Packed and Immutable arrays resulting in the performance difference to drop considerably. Here is the same test on php7.1 here;
http://sandbox.onlinephpfunctions.com/code/2a9e986690ef8505490489581c1c0e70f20d26d1

$max = 770000; //large enough number within memory allocation
$arr = range(1,$max,3);
$arr2 = range(1,$max,2);
$arr = array_merge($arr,$arr2);

$time = -microtime(true);
$res1 = array_unique($arr);
$time += microtime(true);
echo "deduped to ".count($res1)." in ".$time;
// deduped to 513333 in 1.0876770019531

$time = -microtime(true);
$res2 = array();
foreach($arr as $key=>$val) {   
    $res2[$val] = true;
}
$res2 = array_keys($res2);
$time += microtime(true);
echo "<br />deduped to ".count($res2)." in ".$time;
// deduped to 513333 in 0.054931879043579
up
91
Anonymous
12 years ago
It's often faster to use a foreache and array_keys than array_unique:

    <?php

    $max
= 1000000;
   
$arr = range(1,$max,3);
   
$arr2 = range(1,$max,2);
   
$arr = array_merge($arr,$arr2);

   
$time = -microtime(true);
   
$res1 = array_unique($arr);
   
$time += microtime(true);
    echo
"deduped to ".count($res1)." in ".$time;
   
// deduped to 666667 in 32.300781965256

   
$time = -microtime(true);
   
$res2 = array();
    foreach(
$arr as $key=>$val) {   
       
$res2[$val] = true;
    }
   
$res2 = array_keys($res2);
   
$time += microtime(true);
    echo
"<br />deduped to ".count($res2)." in ".$time;
   
// deduped to 666667 in 0.84372591972351

   
?>
up
5
Fabiano
4 years ago
As for PHP 7.1.12, this is the comparison between array_keys(array_flip()), array_flip(array_flip()), for each elimination and array_unique. The array_keys(array_flip()) is the fastest method to remove duplication values from a single dimension array:

<?php

$max
= 1000000;
$arr = range(1,$max,3);
$arr2 = range(1,$max,2);
$arr = array_merge($arr,$arr2);

$time = -microtime(true);
$res1 = array_unique($arr);
$time += microtime(true);

echo
"<br>deduped to ".count($res1)." in ".$time;
// deduped to 666667 in 0.78185796737671
// memory used: 33558528

$time = -microtime(true);
$res2 = array_flip(array_flip($arr));
$time += microtime(true);

echo
"<br><br>deduped to ".count($res2)." in ".$time;
// deduped to 666667 in 0.072191953659058
// memory used: 3774873

$time = -microtime(true);
$res3 = array();
foreach(
$arr as $key=>$val) {
   
$res3[$val] = true;
}
$res3 = array_keys($res3);
$time += microtime(true);

echo
"<br /><br>deduped to ".count($res3)." in ".$time;
// deduped to 666667 in 0.095494985580444
// memory used: 33558528

$time = -microtime(true);
$res4 = array_keys(array_flip($arr));
$time += microtime(true);

echo
"<br /><br>deduped to ".count($res4)." in ".$time;
// deduped to 666667 in 0.05807900428772
// memory used: 33558528
up
22
Ray dot Paseur at SometimesUsesGmail dot com
14 years ago
I needed to identify email addresses in a data table that were replicated, so I wrote the array_not_unique() function:

<?php

function array_not_unique($raw_array) {
   
$dupes = array();
   
natcasesort($raw_array);
   
reset ($raw_array);

   
$old_key    = NULL;
   
$old_value    = NULL;
    foreach (
$raw_array as $key => $value) {
        if (
$value === NULL) { continue; }
        if (
$old_value == $value) {
           
$dupes[$old_key]    = $old_value;
           
$dupes[$key]        = $value;
        }
       
$old_value    = $value;
       
$old_key    = $key;
    }
return
$dupes;
}

$raw_array     = array();
$raw_array[1]    = 'abc@xyz.com';
$raw_array[2]    = 'def@xyz.com';
$raw_array[3]    = 'ghi@xyz.com';
$raw_array[4]    = 'abc@xyz.com'; // Duplicate

$common_stuff    = array_not_unique($raw_array);
var_dump($common_stuff);
?>
up
28
mnbayazit
14 years ago
Case insensitive; will keep first encountered value.

<?php

function array_iunique($array) {
   
$lowered = array_map('strtolower', $array);
    return
array_intersect_key($array, array_unique($lowered));
}

?>
up
3
keneks at gmail dot com
15 years ago
Taking the advantage of array_unique, here is a simple function to check if an array has duplicate values.

It simply compares the number of elements between the original array and the array_uniqued array.

<?php

function array_has_duplicates(array $array)
{
   
$uniq = array_unique($array);
    return
count($uniq) != count($array);
}

?>
up
1
contact at evoweb dot fr
1 year ago
Here is a solution to make unique values keeping empty values for an array with keys :

<?php
function array_unique_kempty($array) {
   
$values = array_unique($array);
   
$return = array_combine(array_keys($array), array_fill(0,count($array),null));
    return
array_merge($return,$values);
}

$myArray = [
   
"test1" => "aaa",
   
"test2" => null,
   
"test3" => "aaa",
   
"test4" => "bbb",
   
"test5" => null,
   
"test6" => "ccc",
   
"test7" => "ddd",
   
"test8" => "ccc"
];

echo
"<pre>".print_r(array_unique_kempty($myArray),true)."</pre>";

/*
Array
(
    [test1] => aaa
    [test2] =>
    [test3] =>
    [test4] => bbb
    [test5] =>
    [test6] => ccc
    [test7] => ddd
    [test8] =>
)
*/
?>
up
1
calexandrepcjr at gmail dot com
5 years ago
Following the Ghanshyam Katriya idea, but with an array of objects, where the $key is related to object propriety that you want to filter the uniqueness of array:

<?php
function obj_multi_unique($obj, $key = false)
    {
       
$totalObjs = count($obj);
        if (
is_array($obj) && $totalObjs > 0 && is_object($obj[0]) && ($key && !is_numeric($key))) {
            for (
$i = 0; $i < $totalObjs; $i++) {
                if (isset(
$obj[$i])) {
                    for (
$j = $i + 1; $j < $totalObjs; $j++) {
                        if (isset(
$obj[$j]) && $obj[$i]->{$key} === $obj[$j]->{$key}) {
                            unset(
$obj[$j]);
                        }
                    }
                }
            }
            return
array_values($obj);
        } else {
            throw new
Exception('Invalid argument or your array of objects is empty');
        }
    }
?>
up
13
mostafatalebi at rocketmail dot com
8 years ago
If you find the need to get a sorted array without it preserving the keys, use this code which has worked for me:

<?php

$array
= array("hello", "fine", "good", "fine", "hello", "bye");

$get_sorted_unique_array = array_values(array_unique($array));

?>

The above code returns an array which is both unique and sorted from zero.
up
19
regeda at inbox dot ru
12 years ago
recursive array unique for multiarrays

<?php
function super_unique($array)
{
 
$result = array_map("unserialize", array_unique(array_map("serialize", $array)));

  foreach (
$result as $key => $value)
  {
    if (
is_array($value) )
    {
     
$result[$key] = super_unique($value);
    }
  }

  return
$result;
}
?>
up
3
sashasimkin at gmail dot com
10 years ago
My object unique function:

<?php
function object_unique( $obj ){
   
$objArray = (array) $obj;

   
$objArray = array_intersect_assoc( array_unique( $objArray ), $objArray );

    foreach(
$obj as $n => $f ) {
        if( !
array_key_exists( $n, $objArray ) ) unset( $obj->$n );
    }

    return
$obj;
}
?>

And these code:

<?php
class Test{
    public
$pr0 = 'string';
    public
$pr1 = 'string1';
    public
$pr2 = 'string';
    public
$pr3 = 'string2';
}

$obj = new Test;

var_dump( object_unique( $obj ) );
?>

returns:
object(Test)[1]
  public 'pr0' => string 'string' (length=6)
  public 'pr1' => string 'string1' (length=7)
  public 'pr3' => string 'string2' (length=7)
up
6
agarcia at rsn dot com dot co
16 years ago
This is a script for multi_dimensional arrays

<?php
function remove_dup($matriz) {
   
$aux_ini=array();
   
$entrega=array();
    for(
$n=0;$n<count($matriz);$n++)
    {
       
$aux_ini[]=serialize($matriz[$n]);
    }
   
$mat=array_unique($aux_ini);
    for(
$n=0;$n<count($matriz);$n++)
    {
       
           
$entrega[]=unserialize($mat[$n]);
       
    }
    return
$entrega;
}
?>
up
3
Ludovico Grossi
7 years ago
[Editor's note: please note that this will not work well with non-scalar values in the array. Array keys can not be arrays themselves, nor streams, resources, etc. Flipping the array causes a change in key-name]

You can do a super fast version of array_unique directly in PHP, even faster than the other solution posted in the comments!

Compared to the built in function it is 20x faster! (2x faster than the solution in the comments).

<?php
function superfast_array_unique($array) {
    return
array_keys(array_flip($array));
}
?>

This works faster for small and big arrays.
up
5
quecoder at gmail
13 years ago
another method to get unique values is :

<?php
$alpha
=array('a','b','c','a','b','d','e','f','f');

$alpha= array_keys(array_count_values($alpha));

print_r($alpha);
?>

Output:
Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f )
up
3
subhrajyoti dot de007 at gmail dot com
4 years ago
Simple and clean way to get duplicate entries removed from a multidimensional array.

<?php
          $multi_array
= $multi_array [0];
         
$multi_array = array_unique($multi_array);
         
print_r($multi_array);
?>
up
2
jusvalceanu - SPAM at SPAM - yahoo dot com
13 years ago
so .... my problem was multidimensional sort.

<?php
      $new
= array();
     
$exclude = array("");
      for (
$i = 0; $i<=count($attribs)-1; $i++) {
         if (!
in_array(trim($attribs[$i]["price"]) ,$exclude)) { $new[] = $attribs[$i]; $exclude[] = trim($attribs[$i]["price"]); }
      }

?>

Array $attribs is an array contaning arrays. Each array in the $attrib array consists in multiple fields (ex: name, lenght, price, etc.) to be more simpler in speech think that $attrib is the array resulted by a search sql query done by a visitator on your online shoopping website ... (so ... each array in the $attrib is a product :P) if you want to sort only the uniq results use the above or use this:

<?php
 
  
/* Our Array of products */
  
$attribs[] = array(
                          
"name"         => "Test Product 1",
                          
"length"     => "42 cm",
                          
"weight"     => "0,5 kg",
                          
"price"     => "10 $",
                          
"stock"     => "100",
                        );

  
$attribs[] = array(
                          
"name"         => "Test Product 2",
                          
"length"     => "42 cm",
                          
"weight"     => "1,5 kg",
                          
"price"     => "10 $",
                          
"stock"     => "200",
                        );

   
/* The nice stuff */

     
$new = array();
     
$exclude = array("");
      for (
$i = 0; $i<=count($attribs)-1; $i++) {
         if (!
in_array(trim($attribs[$i]["price"]) ,$exclude)) { $new[] = $attribs[$i]; $exclude[] = trim($attribs[$i]["price"]); }
      }
     
     
print_r($new); // $new is our sorted array

?>

Have fun tweaking this ;)) i know you will ;))

From Romania With Love
up
2
webmaster at jukkis dot net
14 years ago
Another way to 'unique column' an array, in this case an array of objects:
Keep the desired unique column values in a static array inside the callback function for array_filter.

Example:
<?php
/* example object */
class myObj {
  public
$id;
  public
$value;
  function
__construct( $id, $value ) {
   
$this->id = $id;
   
$this->value = $value;
  }
}

/* callback function */
function uniquecol( $obj ) {
  static
$idlist = array();

  if (
in_array( $obj->id, $idlist ) )
    return
false;

 
$idlist[] = $obj->id;
  return
true;   
}

/* a couple of arrays with second array having an element with same id as the first */
$list  = array( new myObj( 1, ), new myObj( 2, 100 ) );
$list2 = array( new myObj( 1, 10 ), new myObj( 3, 100 ) );
$list3 = array_merge( $list, $list2 );

$unique = array_filter( $list3, 'uniquecol' );
print_r( $list3 );
print_r( $unique );

?>

In addition, use array_merge( $unique ) to reindex.
up
1
zoolyka at gmail dot com
6 years ago
I found the simplest way to "unique" multidimensional arrays as follows:

<?php

$array
= array(
   
'a' => array(1, 2),
   
'b' => array(1, 2),
   
'c' => array(2, 2),
   
'd' => array(2, 1),
   
'e' => array(1, 1),
);

$array = array_map('json_encode', $array);
$array = array_unique($array);
$array = array_map('json_decode', $array);

print_r($array);

?>

As you can see "b" will be removed without any errors or notices.
up
2
amri [ at t] dhstudio dot eu
12 years ago
I searched how to show only the de-duplicate elements from array, but failed.
Here is my solution:

<?php
function arrayUniqueElements($array)
{
return
array_unique(array_diff_assoc($array1,array_unique($array1)));
};
?>

Example:
<?php
$arr1
= array('foo', 'bar', 'xyzzy', '&', 'xyzzy',
'baz', 'bat', '|', 'xyzzy', 'plugh',
'xyzzy', 'foobar', '|', 'plonk', 'xyzzy',
'apples', '&', 'xyzzy', 'oranges', 'xyzzy',
'pears','foobar');

$result=arrayUniqueElements($arr1);
print_r($result);exit;
?>

Output:

Array
(
[4] => xyzzy
[12] => |
[16] => &
[21] => foobar
)
up
1
csaba at alum dot mit dot edu
18 years ago
The following is an efficient, adaptable implementation of array_unique which always retains the first key having a given value:

<?php
function array_unique2(&$aray) {
   
$aHash = array();
    foreach (
$aray as $key => &$val) if (@$aHash[$val]++) unset ($aray[$key]);
}
?>

It is also adaptable to multi dimensional arrays.  For example, if your array is a sequence of (multidimensional) points, then in place of @$aHash[$val]++ you could use @$aHash[implode("X",$val)]++
If you want to not have holes in your array, you can do an array_merge($aray) at the end.

Csaba Gabor
up
0
Sbastien
1 month ago
Because of PHP comparaisons modalities, you can never distinguish null from others falsy values.
Note the absorbing nature of true and false booleans in mix types array.

<?php

$a
= [true, false, null, '', '0', '123', 0, 123];
foreach ([
'SORT_REGULAR', 'SORT_NUMERIC', 'SORT_STRING', 'SORT_LOCALE_STRING'] as $flag) {
   
$a_new = array_unique($a, constant($flag));
    echo
"{$flag} ==> ";
   
var_dump($a_new);
}

/*

Gives :

SORT_REGULAR ==> array(2) {
  [0]=> bool(true)
  [1]=> bool(false)
}
SORT_NUMERIC ==> array(3) {
  [0]=> bool(true)
  [1]=> bool(false)
  [5]=> string(3) "123"
}
SORT_STRING ==> array(4) {
  [0]=> bool(true)
  [1]=> bool(false)
  [4]=> string(1) "0"
  [5]=> string(3) "123"
}
SORT_LOCALE_STRING ==> array(4) {
  [0]=> bool(true)
  [1]=> bool(false)
  [4]=> string(1) "0"
  [5]=> string(3) "123"
}

*/
up
0
dirk dot avery a t gmail
13 years ago
Although array_unique is not intended to work with multi-dimensional arrays, it does on 5.2.9.  However, it does not for 5.2.5.  Beware.
up
0
Dorphalsig
13 years ago
I had a problem with array_unique and multidimensional arrays ... Maybe there's a better way to do this, but this will work for any dimensional arrays.

<?php
function arrayUnique($myArray)
{
    if(!
is_array($myArray))
           return
$myArray;

    foreach (
$myArray as &$myvalue){
       
$myvalue=serialize($myvalue);
    }

   
$myArray=array_unique($myArray);

    foreach (
$myArray as &$myvalue){
       
$myvalue=unserialize($myvalue);
    }

    return
$myArray;

}
?>
up
0
PHP Expert
14 years ago
Case insensitive for PHP v4.x and up.

<?php

function in_iarray($str, $a) {
    foreach (
$a as $v) {
        if (
strcasecmp($str, $v) == 0) {
            return
true;
        }
    }
    return
false;
}

function
array_iunique($a) {
   
$n = array();
    foreach (
$a as $k => $v) {
        if (!
in_iarray($v, $n)) {
           
$n[$k]=$v;
        }
    }
    return
$n;
}

$input = array("aAa","bBb","cCc","AaA","ccC","ccc","CCC","bBB","AAA","XXX");
$result = array_iunique($input);
print_r($result);

/*
Array
(
    [0] => aAa
    [1] => bBb
    [2] => cCc
    [9] => XXX
)
*/
?>
up
0
geuis dot teses at gmail dot com
15 years ago
Here's the shortest line of code I could find/create to remove all duplicate entries from an array and then reindex the keys.

<?php

// Fruits, vegetables, and other food:
$var = array('apple','banana','carrot','cat','dog','egg','eggplant','fish');

$var = array_values(array_unique($var));
?>
up
0
memandeemail at gmail dot com
16 years ago
Problem:
I have loaded an array with the results of a database
query.  The Fields are 'FirstName' and 'LastName'.

I would like to find a way to contactenate the two
fields, and then return only unique values for the
array.  For example, if the database query returns
three instances of a record with the FirstName John
and the LastName Smith in two distinct fields, I would
like to build a new array that would contain all the
original fields, but with John Smith in it only once.
Thanks for: Colin Campbell

Solution:

<?php
/**
* The same thing than implode function, but return the keys so
*
* <code>
* $_GET = array('id' => '4587','with' => 'key');
* ...
* echo shared::implode_with_key('&',$_GET,'='); // Resultado: id=4587&with=key
* ...
* </code>
*
* @param string $glue Oque colocar entre as chave => valor
* @param array $pieces Valores
* @param string $hifen Separar chave da array do valor
* @return string
* @author memandeemail at gmail dot com
*/
function implode_with_key($glue = null, $pieces, $hifen = ',') {
 
$return = null;
  foreach (
$pieces as $tk => $tv) $return .= $glue.$tk.$hifen.$tv;
  return
substr($return,1);
}

/**
* Return unique values from a tree of values
*
* @param array $array_tree
* @return array
* @author memandeemail at gmail dot com
*/
function array_unique_tree($array_tree) {
 
$will_return = array(); $vtemp = array();
  foreach (
$array_tree as $tkey => $tvalue) $vtemp[$tkey] = implode_with_key('&',$tvalue,'=');
  foreach (
array_keys(array_unique($vtemp)) as $tvalue) $will_return[$tvalue] = $array_tree[$tvalue];
  return
$will_return;
}

$problem = array_fill(0,3,
array(
'FirstName' => 'John', 'LastName' => 'Smith')
);

$problem[] = array('FirstName' => 'Davi', 'LastName' => 'S. Mesquita');
$problem[] = array('FirstName' => 'John', 'LastName' => 'Tom');

print_r($problem);

print_r(array_unique_tree($problem));
?>
To Top