array_combine

If two keys are the same, the second one prevails. Example:<?phpprint_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:<?phpfunction 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)

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_functionReason: see security issue flagged up in the documentation concerning create_function<?phpfunction 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;}?>

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:<?phpfunction array_real_combine($a, $b){    return $a===array() && $b===array() ? array() : array_combine($a, $b);}?>

<?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 )
?>

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

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 $b is an array of the current row retrieved with fgetcsv()<?phpfunction array_combine_special($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);}?>

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;}

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        ))

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.

I recently had to flip an array and group the elements by value, this snippet will do that:<?phpfunction 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        ))

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 */?>

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;
}
?>

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)));