array_combine

(PHP 5, PHP 7)

array_combine — Creates an array by using one array for keys and another for its values

Description

array array_combine ( array $keys , array $values )

Creates an array by using the values from the keys array as keys and the values from the values array as the corresponding values.

Parameters

keys: Array of keys to be used. Illegal values for key will be converted to string.
values: Array of values to be used

Return Values

Returns the combined array, FALSE if the number of elements for each array isn't equal.

Errors/Exceptions

Throws E_WARNING if the number of elements in keys and values does not match.

Changelog

Version	Description
5.4.0	Previous versions issued `E_WARNING` and returned `FALSE` for empty arrays.

Examples

Example #1 A simple array_combine() example


<?php
$a = array('green', 'red', 'yellow');
$b = array('avocado', 'apple', 'banana');
$c = array_combine($a, $b);

print_r($c);
?>

The above example will output:

Array
(
    [green]  => avocado
    [red]    => apple
    [yellow] => banana
)

User Contributed Notes

loureirorg at gmail dot com

3 years ago


If two keys are the same, the second one prevails. 

Example:
<?php
print_r(array_combine(Array('a','a','b'), Array(1,2,3)));
?>
Returns:
Array
(
    [a] => 2
    [b] => 3
)

But if you need to keep all values, you can use the function below:

<?php
function array_combine_($keys, $values)
{
    $result = array();
    foreach ($keys as $i => $k) {
        $result[$k][] = $values[$i];
    }
    array_walk($result, create_function('&$v', '$v = (count($v) == 1)? array_pop($v): $v;'));
    return    $result;
}

print_r(array_combine_(Array('a','a','b'), Array(1,2,3)));
?>
Returns:
Array
(
    [a] => Array
        (
            [0] => 1
            [1] => 2
        )

    [b] => 3
)

claude dot pache at gmail dot com

5 years ago


array_combine() has a strange bug/misfeature (as of PHP 5.3.2): There is no logical reason for <? array_combine(array(), array()) ?> throwing a warning and returning FALSE, instead of returning <? array() ?> (see http://bugs.php.net/bug.php?id=34857). Here is a quick workaround:
<?php
function array_real_combine($a, $b)
{
    return $a===array() && $b===array() ? array() : array_combine($a, $b);
}
?>

zequez at gmail dot com

5 years ago


If two keys are the same, the second one prevails.
Example:
<?php
print_r(array_combine(Array('a','a','b'), Array(1,2,3)));
?>
Returns:
Array
(
    [a] => 2
    [b] => 3
)

quecoder at gmail

7 years ago


<?php

// If they are not of same size, here is solution:



$abbreviations = array("AL", "AK", "AZ", "AR", "TX", "CA");

$states = array("Alabama", "Alaska", "Arizona", "Arkansas");

function combine_arr($a, $b)

{

    $acount = count($a);

    $bcount = count($b);

    $size = ($acount > $bcount) ? $bcount : $acount;

    $a = array_slice($a, 0, $size);

    $b = array_slice($b, 0, $size);

    return array_combine($a, $b);

}

$combined = combine_arr($abbreviations, $states);

print_r($combined); 



//  Output

//  Array ( [AL] => Alabama [AK] => Alaska [AZ] => Arizona 

//  [AR] => Arkansas )

?>

neoyahuu at yahoo dot com

9 years ago


Some tips for merging same values in an array

<?php
$array1 = array(1,2,3,4,5,6,7,8,9,10,11,12);
$array2 = array(1,2,3,13);

$merged = array_merge($array1,$array2);

// output normal array_merge
echo '<pre>After array_merge :
';
print_r($merged);
echo '</pre>';

// do double flip for merging values in an array
$merged = array_flip($merged);
$merged = array_flip($merged);

// Output after
echo '<pre>After Double Flip : 
';
print_r($merged);
echo '</pre>';
?>

Output ::

After array_merge :
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
    [9] => 10
    [10] => 11
    [11] => 12
    [12] => 1
    [13] => 2
    [14] => 3
    [15] => 13
)

After Double Flip : 
Array
(
    [12] => 1
    [13] => 2
    [14] => 3
    [3] => 4
    [4] => 5
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
    [9] => 10
    [10] => 11
    [11] => 12
    [15] => 13
)

Khaly

8 years ago


This is the function for PHP4 :



<?php



function array_combine($arr1,$arr2) {

   $out = array();

   foreach($arr1 as $key1 => $value1)    {

    $out[$value1] = $arr2[$key1];

   }

   return $out

}



?>

dejiakala at gmail dot com

4 years ago


I needed to read CSV files into associative arrays with column headers as keys. Then I ran into a problem when you have empty columns at the end of a row because array_combine returns false if both arrays don't have the same number of elements. This function based on quecoder at gmail's combine_arr() below allowed me to pad either array or not when parsing my CSVs to arrays.
$a is the array of header columns and $b is an array of the current row retrieved with fgetcsv()

<?php

function array_combine_special($a, $b, $pad = TRUE) {
    $acount = count($a);
    $bcount = count($b);
    // more elements in $a than $b but we don't want to pad either
    if (!$pad) {
        $size = ($acount > $bcount) ? $bcount : $acount;
        $a = array_slice($a, 0, $size);
        $b = array_slice($b, 0, $size);
    } else {
        // more headers than row fields
        if ($acount > $bcount) {
            $more = $acount - $bcount;
            // how many fields are we missing at the end of the second array?
            // Add empty strings to ensure arrays $a and $b have same number of elements
            $more = $acount - $bcount;
            for($i = 0; $i < $more; $i++) {
                $b[] = "";
            }
        // more fields than headers
        } else if ($acount < $bcount) {
            $more = $bcount - $acount;
            // fewer elements in the first array, add extra keys        
            for($i = 0; $i < $more; $i++) {
                $key = 'extra_field_0' . $i;
                $a[] = $key;
            }
            
        }
    }
    
    return array_combine($a, $b);
}
?>

welcome at el hyphen mustafa

5 months ago


Further to loreiorg's script 
in order to preserve duplicate keys when combining arrays.

I have modified the script to use a closure instead of create_function

Reason: see security issue flagged up in the documentation concerning create_function

<?php

function array_combine_($keys, $values){
    $result = array();

    foreach ($keys as $i => $k) {
     $result[$k][] = $values[$i];
     }

    array_walk($result, function(&$v){
     $v = (count($v) == 1) ? array_pop($v): $v;
     });

    return $result;
}

?>

ilanfir at gmail dot com

1 year ago


I recently had to flip an array and group the elements by value, this snippet will do that:
<?php
function flipAndGroup($input) {
    $outArr = array();
    array_walk($input, function($value, $key) use (&$outArr) {
        if(!isset($outArr[$value]) || !is_array($outArr[$value])) {
            $outArr[$value] = [];
        }
        $outArr[$value][] = $key;
    });
    return $outArr;
}
?>

Example:
<?php
$users_countries = array(
    'username1' => 'US',
    'user2' => 'US',
    'newuser' => 'GB'
);
print_r(flipAndGroup($users_countries));
?>

Returns:
Array
(
    [US] => Array
        (
            [0] => username1
            [1] => user2
        )

    [GB] => Array
        (
            [0] => newuser
        )
)

info at maisuma dot jp

1 year ago


array_combine() returns NULL instrad of FALSE, when non-array parameters are given (issuing warning).

<?php
  //NULL
  var_dump(array_combine('string',array(42)));
?>

ismorodin at hotmail dot com

1 year ago


Function eliminates the error Throws E_WARNING if the number of elements in keys and values does not match.

function arrCombine($arr1 = array(),$arr2 = array()){
            if(is_array($arr1) && is_array($arr2)):
                $cntArr1 = count($arr1);
                $cntArr2 = count($arr2);
                $difference = max($cntArr1,$cntArr2) - min($cntArr1,$cntArr2);
                if($cntArr1 > $cntArr2):
                    for ($i=1;$i<=$difference;$i++){
                        $arr2[$cntArr2+$i] = $cntArr2 + 1;
                    }
                    return array_combine($arr1,$arr2);
                elseif($cntArr1 < $cntArr2):
                    for ($i=1;$i<=$difference;$i++){
                        $arr1[$cntArr1+$i] = count($arr1) + 1;
                    }
                    return array_combine($arr1,$arr2);
                else:
                    return array_combine($arr1,$arr2);
                endif;
            endif;
    }
$array = [1,4,5,6,7,8];
$array2 = ['john','smith'];

var_dump( arrCombine($array,$array2 ));

array (size=6)
  1 => string 'john' (length=4)
  4 => string 'smith' (length=5)
  5 => int 3
  6 => int 3
  7 => int 3
  8 => int 3

var_dump( arrCombine($array2,$array) );

array (size=6)
  'john' => int 1
  'smith' => int 4
  3 => int 5
  4 => int 6
  5 => int 7
  6 => int 8

g.REMOVETHIS.vincendon AT vithemis.com

3 years ago


I was looking for a function that could combine an array to multiple one, for my MySQL GROUP_CONCAT() query, so I made this function.

<?php
    function array_combine_array(array $keys)
    {
        $arrays = func_get_args();
        $keys = array_shift($arrays);
        
        /* Checking if arrays are on the same model (array('INDEX'=> array()) or array()) */
        $check = count(array_unique(array_map('is_array',array_map('current',$arrays)))) === 1;
        if (!$check) { trigger_error('Function array_combine_array() expects all parameters to be same type array or array of array',E_USER_NOTICE); return array(); }
        
        /* Checking the model of arrays, array('INDEX' => array()) or Array() */
        $assocArray = is_array(array_shift(array_map('current',$arrays)));
        
        /* If empty $Keys is given, we fill an empty array */
        if (empty($keys)) $keys = array_keys(array_fill(0,max(($assocArray) ? array_map('count',array_map('current',$arrays)) : array_map('count',$arrays)),'foo'));

        /* Init */
        $ret=array();$i=0;
        /* Cycling on each keys values, making an offset for each */
        foreach($keys as $v)
        {
            /* Cycling on arrays */
            foreach ($arrays as $k)
            {
                if ($assocArray)
                {
                    /* Getting the index of the element */
                    $key = key($k);
                    /* If the offset exists, we place it */
                    $ret[$v][$key] = isset($k[$key][$i]) ? $k[$key][$i]:false;
                }
                /* Making the array with auto-made index */
                else
                    $ret[$v][] = isset($k[$i]) ? $k[$i]: false;
            }
            /* Getting the next offset */
            $i++;
        }
        return $ret;
    }

    /* Examples */
    $r = array(1,2,4,10);

    $a1 = array('one','two','four','ten');
    $a2 = array('un','deux','quatre','dix');
    $a3 = array('uno','dos','quatro','diez');
     
     print_r(array_combine_array($r,array('english' => $a1),array('french' => $a2),array('spanish' => $a3))); /* Associative index, associative subarray indexes */
     print_r(array_combine_array($r,$a1,array('french' => $a2),array('spanish' => $a3))); /* Ouputs Error */
     print_r(array_combine_array($r,$a1,$a2,$a3)); /* Associative index, auto-made subarray indexes */
     print_r(array_combine_array(array(),array('english' => $a1),array('french' => $a2),array('spanish' => $a3))); /* Auto-made index, associative subarray indexes */
?>

Dan LaManna

4 years ago


I needed a function that truncated extra values, and only went as far as keys without throwing a warning as array_combine does.



<?php

function safeArrayCombine($keys, $values) {

    $combinedArray = array();

        

    for ($i=0, $keyCount = count($keys); $i < $keyCount; $i++) {

         $combinedArray[$keys[$i]] = $values[$i];

    }

        

    return $combinedArray;

}

?>

aaron at aaronholmes dot net

3 years ago


You can create an array hashset from a flat array, storing both keys and values, with array_combine(). This works with duplicate values in the array too.

<?php
$flat_array = array(
        'one',
        'two',
        'three',
        'three',
        'four',
        'one'
);

$set = array_combine($flat_array, $flat_array);

var_dump($set);
?>

This outputs the following:

array(4) {
    ["one"]=>
        string(3) "one"
    ["two"]=>
        string(3) "two"
    ["three"]=>
        string(5) "three"
    ["four"]=>
        string(4) "four"
}

J.D.D.

7 years ago


This may be obvious, but I don't see anything about it on the manual page, so a friendly warning...  The array you are using as keys must have all unique values.  If not, array elements get dropped.  



<?php

$arr_notUnique = array('one' , 'one' , 'two');

$arr_b = array('red' , 'green' , 'blue');



$arr_combo = array_combine($arr_notUnique, $arr_b);

?>



Results:  Array ( [one] => green [two] => blue )



NOT:  Array ( [one] => red [one] => green [two] => blue )

bradentkeith at dot dontspam dot gmail dot com

6 years ago


I needed a function that would take keys from one unequal array and combine them with the values of another. Real life application:
Select 4 product types.
Each product has a serial.
There are 4 sets of products.

    <?php
        function array_combine2($arr1, $arr2) {
            $count1 = count($arr1);
            $count2 = count($arr2);
            $numofloops = $count2/$count1;
                
            $i = 0;
            while($i < $numofloops){
                $arr3 = array_slice($arr2, $count1*$i, $count1);
                $arr4[] = array_combine($arr1,$arr3);
                $i++;
            }
            
            return $arr4;
        }
    ?>

Input:
Array
(
    [0] => SMART Board
    [1] => Projector
    [2] => Speakers
    [3] => Splitter
)
, Array
(
    [0] => serial to smart board1
    [1] => serial to projector 1
    [2] => serial to speakers 1
    [3] => serials to splitter 1
    [4] => serials to smart board 2
    [5] => serials to projector 2
    [6] => serials to speakers 2
    [7] => serials to splitter 2
)

Array
(
    [0] => Array
        (
            [SMART Board] => serial to smart board1
            [Projector] => serial to projector 1
            [Speakers] => serial to speakers 1
            [Splitter] => serials to splitter 1
        )

    [1] => Array
        (
            [SMART Board] => serials to smart board 2
            [Projector] => serials to projector 2
            [Speakers] => serials to speakers 2
            [Splitter] => serials to splitter 2
        )

)

Mike Jean

8 years ago


Khaly's PHP4 code below does not work correctly in all cases. Consider when your array consists of floats:

<?php

$okay = array(0, 10, 20, 30);
$not_okay = array(0, 0.5, 1, 1.5);

$foo = array_combine($okay, $okay);
$bar = array_combine($not_okay, $not_okay);

/* 

Results:

$foo = {
  [0]=> int(0)
  [10]=> int(10)
  [20]=> int(20)
  [30]=> int(30)
}

$bar = {
  [0]=> float(0.5)
  [1]=> float(1.5)
}

*/

?>

What can you do? In my case, I was just zipping up some select-box options, so I converted everything in my floats to strings.

xavier at api-meal dot eu

6 years ago


<?php
/**
 * Return alternatives defined by values of each parameters.
 *
 * Exemple :
 *
 * array_alternatives(array('foo','bar'), array('baz', 'qux'));
 * array(
 *     array('foo', 'baz'),
 *     array('bar', 'baz'),
 *     array('foo', 'qux'),
 *     array('bar', 'qux'),
 * );
 * 
 * array_alternatives(array('a'), array('simple-minded'), array('solution'));
 * array(
 *     array('a', 'simple-minded', 'solution')
 * );
 * 
 * array_alternatives(array('a'), array('red', 'blue'), array('car'));
 * array(
 *     array('a', 'red',  'car'),
 *     array('a', 'blue', 'car'),
 * );
 *  
 * @param array $first_element
 * @param array $second_element
 * @return array
 * @author Xavier Barbosa
 */
function array_alternatives(array $first_element, array $second_element)
{
    $lists = func_get_args();
    $total_lists = func_num_args();
    
    for($i=0; $i<$total_lists; $i++)
    {
        $list =& $lists[$i];
        if (is_array($list) === FALSE)
            throw new Exception("Parameter $i is not an array.");
        if (count($list) === 0)
            throw new Exception("Parameter $i has no element.");
        unset($list);
    }
    
    // Initialize our alternatives
    $alternatives = array();
    foreach($lists[0] as &$value)
    {
        array_push($alternatives, array($value));
        unset($value);
    }
    unset($lists[0]);
    
    // Process alternatives
    for($i=1; $i<$total_lists; $i++)
    {
        $list =& $lists[$i];
        
        $new_alternatives = array();
        foreach($list as &$value)
        {
            foreach($alternatives as $_)
            {
                array_push($_, $value);
                array_push($new_alternatives, $_);
            }
        }
        
        // Rotate references, it's cheaper than copy array like `$alternatives = $new_alternatives;`
        $alternatives =& $new_alternatives;
        unset($new_alternatives, $list, $lists[$i]);
    }
    
    return $alternatives;
}
?>

array_combine

Description

Parameters

Return Values

Errors/Exceptions

Changelog

Examples

See Also

User Contributed Notes