array_combine

(PHP 5, PHP 7, PHP 8)

array_combine — 一方の配列をキーとして、もう一方の配列を値として、ひとつの配列を生成する

説明

array_combine(array $keys, array $values): array

keys 配列の値をキーとして、また values 配列の値を対応する値として生成した配列を作成します。

パラメータ

keys: キーとして使用する配列。無効な値を渡すと文字列に変換されます。
values: 値として使用する配列。

戻り値

作成した配列を返します。

エラー / 例外

PHP 8.0.0 以降では、keys および values の要素数が一致しなかった場合は ValueError がスローされます。それより前のバージョンでは、 E_WARNING が発生していました。

変更履歴

バージョン	説明
8.0.0	それぞれの配列の要素数が一致しなかった場合、 array_combine() は ValueError をスローするようになりました。これより前のバージョンでは、`false` を返していました。

例

例1 array_combine()の簡単な例

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

print_r($c);
?>

上の例の出力は以下となります。

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

参考

array_merge() - ひとつまたは複数の配列をマージする
array_walk() - 配列の全ての要素にユーザー定義の関数を適用する
array_values() - 配列の全ての値を返す
array_map() - 指定した配列の要素にコールバック関数を適用する

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User Contributed Notes 13 notes

down

112

loureirorg at gmail dot com ¶

11 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
)

down

claude dot pache at gmail dot com ¶

14 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);
}
?>

down

welcome at el hyphen mustafa ¶

8 years 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;
}

?>

down

quecoder at gmail ¶

16 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 )

?>

down

zequez at gmail dot com ¶

13 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
)

down

dejiakala at gmail dot com ¶

13 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);
}
?>

down

Dan LaManna ¶

13 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;

}

?>

down

g.REMOVETHIS.vincendon AT vithemis.com ¶

12 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 */
?>

down

info at callismart dot com dot ng ¶

3 months ago

As of PHP 8.0, array_combine throws  ValueError if the number of elements for each array is not equal;

To be on a safer side, you can perform a check instead.

$arrayk = array( 'key1', 'key2', 'key3' );
$arrayv = array( 'v1', 'v2', 'v3' );

if ( count( $arrayk ) === count( $arrayv ) ) {
    echo '<pre>';
    var_dump( array_combine( $arrayk, $arrayv ) );
    echo '</pre>';
} else {
   return false;
}

down

ilanfir at gmail dot com ¶

9 years 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
        )
)

down

bradentkeith at dot dontspam dot gmail dot com ¶

14 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
        )

)

down

-1

PHPNewbie ¶

7 years ago

This will seem obvious to some, but if you need to preserve a duplicate key, being you have unique vars, you can switch the array_combine around, to where the vars are the keys, and this will output correctly.

This [default] formula auto-removes the duplicate keys.

$i=0;
foreach (array_combine($keys, $vars) as $key => $var)
{
$i=$i;
echo($key);
echo " ";
echo($var);
}

This formula accomplishes the same thing, in the same order, but the duplicate "keys" (which are now  vars) are kept.

$i=0;
foreach (array_combine($vars, $keys) as $var => $key)
{
$i=$i;
echo($key);
echo " ";
echo($var);
}

I know, I'm a newbie, but perhaps someone else will need this eventually. I couldn't find another solution anywhere.

down

-1

douglasrich9215 at gmail dot com ¶

6 years ago

I had an epiphany when try to handle NON-ASSOCIATIVE array forms in my controller. This little one liner can pretty much edit ANY kind of non-associative array. For example this one just returns an array of values inputed by a new user.

The $data value is the the json_decoded() value of a register form.
Here is used str_replace, you could definitely do a number of things like preg matches and other things. 

$readyToProcessForUser = array_combine(str_replace("new_user_", "", array_keys($data)), $data);

You could also do the same for the values.

$readyToProcessForUser = array_combine(array_keys($data), str_replace("-", "", $data));

Or BOTH!
Use full if you don't want to walk an entire array and the keys through the same callback.

$readyToProcessForUser = array_combine(array_walk('trim', array_keys($data)), array_walk('custom_callback', array_values($data)));

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