uksort

(PHP 4, PHP 5, PHP 7, PHP 8)

uksort — Sort an array by keys using a user-defined comparison function

Description

uksort(array &$array, callable $callback): true

Sorts array in place by keys using a user-supplied comparison function to determine the order.

Note:
If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.

Note:
Resets array's internal pointer to the first element.

Parameters

array: The input array.
callback: The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

callback(mixed $a, mixed $b): int

Caution
Returning non-integer values from the comparison function, such as float, will result in an internal cast to int of the callback's return value. So values such as 0.99 and 0.1 will both be cast to an integer value of 0, which will compare such values as equal.

Return Values

Always returns true.

Changelog

Version	Description
8.2.0	The return type is `true` now; previously, it was bool.
8.0.0	If `callback` expects a parameter to be passed by reference, this function will now emit an `E_WARNING`.

Examples

Example #1 uksort() example

<?php
function cmp($a, $b)
{
    $a = preg_replace('@^(a|an|the) @', '', $a);
    $b = preg_replace('@^(a|an|the) @', '', $b);
    return strcasecmp($a, $b);
}

$a = array("John" => 1, "the Earth" => 2, "an apple" => 3, "a banana" => 4);

uksort($a, "cmp");

foreach ($a as $key => $value) {
    echo "$key: $value\n";
}
?>

The above example will output:

an apple: 3
a banana: 4
the Earth: 2
John: 1

Found A Problem?

Learn How To Improve This Page • Submit a Pull Request • Report a Bug

＋add a note

User Contributed Notes 17 notes

down

580

PHPUser ¶

9 years ago

[Editor's note: the following comment may be factually incorrect]



uksort is only usable in the UK

<?php

if($country=="UK"){

  uksort();

}else{

  echo "You have to live in UK to use uksort().";

}

?>

down

ingo at example dot test ¶

10 years ago

sort with collation, to have umlauts correctly:

uksort($retval, array(Collator::create( 'de_DE' ), 'compare'));

down

fabriceb at gmx dot net ¶

20 years ago

(about sorting an array of objects by their properties in a class - inspired by webmaster at zeroweb dot org at usort function)
I'm using classes as an abstraction for querying records in a database and use arrays of objects to store records that have an 1 to n relationship. E.g. a class "family" has family members stored as an array of objects. Each of those objects prepresents a record in a database related to the family (by it's familyId).

To identify members, I'm using their memberId as the key of the array e.g. $family->members[$memberId].
To sort the family members AFTER fetching them with the database query, you can use the functions _objSort and sortMembers which will sort the "members" array by key using it's properties (for space reasons I didn't include the methods used to open the records):
<?php
class familyMember
{
    var $memberId;
    var $familyId;
    var $firstName;
    var $age;
    var $hairColor;
// ...
}

class family
{
    var $familyId;
    var $name;
    var $members = array(); // array of familyMember objects
    var $sortFields = array();
    var $sortDirections = array();
    // ...
    function _objSort(&$a, &$b, $i = 0)
    {
        $field        = $this->sortFields[$i];
        $direction    = $this->sortDirections[$i];
        
        $diff = strnatcmp($this->details[$a]->$field, $this->details[$b]->$field) * $direction;
        if ($diff == 0 && isset($this->sortFields[++$i]))
        {
            $diff = $this->_objSort($a, $b, $i);
        }
        
        return $diff;
    }
    
    function sortMembers($sortFields)
    {
        $i = 0;
        foreach ($sortFields as $field => $direction)
        {
            $this->sortFields[$i] = $field;
            $direction == "DESC" ? $this->sortDirections[$i] = -1 : $this->sortDirections[$i] = 1;
            $i++;
        }
        
        uksort($this->details, array($this, "_objSort"));
        
        $this->sortFields = array();
        $this->sortDirections = array();
    }
}
// open a family
$familyId = 5;
$family = new family($familyId);
$family->open(); // this will also fetch all members

// sort members by 3 fields
$family->sortMembers(array("firstName" => "ASC", "age" => "DESC", "hairColor" => "ASC"));
// output all family members
foreach ($family->members as $member)
{
    echo $member->firstName." - ".$member->age." - ".$member->hairColor."<br />";
}
?>

Note that this might not be the fastest thing on earth and it hasn't been tested very much yet but I hope it's useful for someone.

down

mdsky at web dot de ¶

14 years ago

Case insensitive without own function:

uksort($array, "strnatcasecmp");

down

aleczapka at gmx dot net ¶

19 years ago

One remark regarding array_sorter class.
It won't work correctly with eg. dates from mysql like 20041206105350, cause you can't convert such number into integer. To fix it remove intval() from the code. If the variable is a number it will work without converting this to int anyways. Here is the fix.

<?php
....
if ($a == $b) 
    return 0;
if ($this->sasc)
    return ($a > $b) ? 1 : -1;
else
    return ($a > $b) ? -1 : 1;
...
?>

down

guss at typo dot co dot il ¶

21 years ago

Regarding the recursive sorting function above:
Genrally speaking, any recursion can be reimplemented using simple iteration. in the specific case, using recursion to compare strings has a huge performance impact while a simple loop would suffice and be faster and more simple. 
Recursion is only good if it simplifies your code or your understanding of the concept. the previous example does neither, especially as it does a lot of repetitive things in each iteration, such as asigning the character order constant, rebuilding it into an array and such

For example, the string comparison could be written as such : 
function str_compare($a,$b) {
    $order="aA??bBcC&#269;&#268;..."; // longer normally & without that html entities
    $default = strlen($a) - strlen($b);
    $minlen = strlen($a) < strlen($b) ? strlen($a) : strlen($b);
    for ($i = 0; $i < $minlen; $i++) {
        $pos_a=strpos($order,$a[$i]);
        $pos_b=strpos($order,$b[$i]);
        if ($pos_a != $pos_b)
            return $pos_a - $pos_b;
    }
    return $default;
}

Which is much simpler and faster.
Note that the above function will break for characters that are not listed in $order. it should be failry trivial to fix it.

down

contacto at hardcode dot com dot ar ¶

15 years ago

need a case insensitive sort by key function? i did and couldn find it, so:



<?php

function insensitive_uksort($a,$b) {

    return strtolower($a)<strtolower($b);

}

uksort($arr, "insensitive_uksort");

?>

down

aleczapka at gmx dot net ¶

20 years ago

down

brian dot short at gmail dot com ¶

15 years ago

If you need to periodically sort by grades (A, A+, D-, etc.), here is a compare function that compares strings by the case-insensitive method, unless it finds a grade, in which case it correctly sorts by putting "plus" grades first, unmarked grades second, and "minus" grades last.



<?php

function cmp($a, $b)

{

   $a = preg_replace('@^(a|an|the) @', '', $a);

   $b = preg_replace('@^(a|an|the) @', '', $b);



   //special code for grades

   if (strpos( $a, "+") !== false || strpos( $b, "+") !== false  || 

       strpos( $a, "-") !== false || strpos( $b, "-") !== false ){



        $substrA = substr($a, 0, 1);

        $substrB = substr($b, 0, 1);        



        $modifierA = (strlen($a) == 2) ? substr($a, 1, 1) : "";

        $modifierB = (strlen($b) == 2) ? substr($b, 1, 1) : "";

    

        if ($substrA == $substrB){

            //figure out plusses and minuses.

            if ($modifierA == "+"){

                return -1;

            } else if ($modifierB == "+"){

                return 1;

            }

        

            if ($modifierA == "-"){

                return 1;

            } else if ($modifierB == '-'){

                return -1;

            }

        } else {

            return strcasecmp($a, $b);

        }

 

    }

   return strcasecmp($a, $b);

}



$grades = array( 

                 "C+" => 13    ,

                "C" => 10     ,

                "D+" => 8     ,

                "B+" => 7     ,

                "C-" => 6     ,

                "A-" => 5     ,

                "F" => 5      ,

                "B" => 4      ,

                "B-" => 4     ,

                "D" => 3      ,

                "D-" => 3     ,

                "A+" => 1

    ); 



uksort($grades, "cmp");

?>



result:  Array

(

    [A+] => 1

    [A-] => 5

    [B+] => 7

    [B] => 4

    [B-] => 4

    [C+] => 13

    [C] => 10

    [C-] => 6

    [D+] => 8

    [D] => 3

    [D-] => 3

    [F] => 5

)

down

smcbride at msn dot com ¶

3 years ago

This might be obvious to many, but just to help others that are trying to use this in a class.  Inside a class, you can prefix the function with self:: within the uksort(), and it will work.  Also, if it is in another class that is included, you can prefix it with the class name.

class someclass {
     private function ArraySortCMPIP($a, $b) {
          $a = ip2long($a);
          $b = ip2long($b);

          if ($a == $b) return 0;
          return ($a < $b) ? -1 : 1;
     }

     // Output
     public function PrintResults() {
          uksort($this->someIPAddressArray, 'self::ArraySortCMPIP');
          print_r($this->someIPAddressArray);
     }
}

down

jg at delegation dot ca ¶

20 years ago

To sort dates with uksort:

function datediff($a, $b) {
    

$a = date('U',$a);
$b = date('U',$b);

if ($a == $b) $r = 0;
else $r = ($a > $b) ? 1: -1;

return $r;
}

down

DimeCadmium ¶

6 years ago

Don't use uksort($array, "strnatcasecmp"); ... use ksort($array, SORT_NATURAL|SORT_FLAG_CASE);

down

Jimomighty ¶

19 years ago

...

function cmp($a, $b)
{
   if ($a == $b) {
       return 0;
   }
   return ($a < $b) ? -1 : 1;
}

function uksort_tree ( &$array )
{
    // [PHP5] foreach ( $array as &$value )
    foreach ( $array as $key => $value )
    {
       if ( is_array ( $value ) )
       {
            // [PHP5] uksort_tree ( $value );
           uksort_tree ( $array[$key] );
       }
    }

    uksort( $array, "cmp" );
}

uksort_tree( $myEntryArray );

...

down

webmaster at kik-it at N0SP4M dot com ¶

20 years ago

The code below allows you to sort an array_A following array_B keys order, original keys and values remain associated.

<?

//main function
Function SortArrayAKeysLikeArrayBKeys(&$TheArrayToSort){
   uksort($TheArrayToSort,"SortArrayAKeysLikeArrayBKeys_cmp");
}

//the custom compare function
Function SortArrayAKeysLikeArrayBKeys_cmp($a,$b){
  global $TheArrayOrder;
  $PosA=KeyPosInArray($a,$TheArrayOrder);
  $PosB=KeyPosInArray($b,$TheArrayOrder);
  if ($PosA==$PosB){return 0;}else{return ($PosA > $PosB ? 1 : -1);}
}

//where is my key in my array
Function KeyPosInArray($Key,$Array){
   $i=0;
   $Pos=99999999;
   if($Array){
      foreach($Array as $K => $V){
         $i++;
         if($K==$Key){
            $Pos=$i;
            break;
         }
      }
   }
   return $Pos;
}

//the array you want to sort
$AnyArrayToSort['age']='19';
$AnyArrayToSort['ville']='rennes';
$AnyArrayToSort['website']='kik-it.com';
$AnyArrayToSort['region']='bretagne';
$AnyArrayToSort['code_postal']='35200';
$AnyArrayToSort['Nom']='Fred';

//the array with the correct keys/values order
$TheArrayOrder['Nom']='Whatever';
$TheArrayOrder['age']='Anything';
$TheArrayOrder['region']='What u want';
$TheArrayOrder['ville']='Something';
$TheArrayOrder['code_postal']='Nothing';

//before sort
print_r($AnyArrayToSort);    
echo "<br>";
//we sort
SortArrayAKeysLikeArrayBKeys($AnyArrayToSort);
echo "<br>";
//after sort
print_r($AnyArrayToSort);
?>

Will print :

Array ( [age] => 19 [ville] => rennes [website] => kik-it.com [region] => bretagne [code_postal] => 35200 [Nom] => Fred ) 

Array ( [Nom] => Fred [age] => 19 [region] => bretagne [ville] => rennes [code_postal] => 35200 [website] => kik-it.com ) 

The keys not listed in the $TheArrayOrder will appear at the end of your sorted array (only if Key Pos < 99999999 ;o)

down

ignatius dot reilly at free dot fr ¶

21 years ago

To use a more complicated comparison function, one can use a callback to a method of an object instance.
For example the following will take an array $arr whose keys are the same as those of $reference, and reorder $arr so that the keys appear in the same order as in $reference.

class kcmp {
    var $reference ;
    function kcmp( $reference ) {
       $this->reference = $reference ; 
    }
    function kcompare( $a, $b ) {
       $keys = array_keys( $this->reference ) ;
       $position_a = array_search( $a, $keys ) ;
       $position_b = array_search( $b, $keys ) ;
       return  $position_a < $position_b ? -1 : 1 ;    
    }
}

$reference = array(
    "k2" => "a2",
    "k3" => "a3",
    "k1" => "a1"
) ;
$arr = array(
    "k1" => "b1",
    "k2" => "b2",
    "k3" => "b3"
) ;
print_r( $arr ) ; 
uksort( $arr, array( new kcmp( $reference ), "kcompare" ) ) ;
print_r( $arr ) ;

down

-1

andi at example dot com ¶

8 years ago

I needed to be able to sort a string that contained numbers eg.

"Slot 1 name"
"Slot 2 name"
"Slot 10 name"

using a normal string compare the "Slot 10 name" would appear before "Slot 2 name" so I wrote little function that will compare a string taking numbers in to consideration. There may be a few edge cases that need to be taken in to consideration.

function strCmpWithNumbers( $a, $b) {
  // Split the string in to words.
  $a = explode(' ',$a);
  $b = explode(' ',$b);
  $loop = 0;
  do {
    // Get the first word from each item
    $ta = Utils::gvfa($a, $loop);
    $tb = Utils::gvfa($b, $loop);
    
    if (isset($ta)) {
      if (isset($tb)) {
        if (is_numeric($ta)) {
          if ($ta != $tb) {
            return $ta - $tb;
          }
        } else {
          $val = strcasecmp($ta, $tb);
          if ($val != 0) {
            return $val;
          }
        }
      } else {
        return 1; // a is set but b isn't
      }
    } else {
      return isset($b);
    }
    $loop +=1;
  } while (true);
}

down

-5

Anonymous ¶

9 years ago

An associative array with known keys can be easily custom sorted using a switch statement in the callback:

NB ksort can be used beforehand to ensure expected results

ksort($array);

uksort($array, function ($a) {                    
    switch($a) {
        case 'pepperoni':
            return 0;
        case 'beef':
            return 1;
        case 'chicken':
            return 2;
        case 'ham':
            return 3;
        case 'vegetarian':
            return 4;
    }
});

＋add a note

uksort

Description

Parameters

Return Values

Changelog

Examples

See Also

Found A Problem?

User Contributed Notes 17 notes