replace array keys with given respective keys

array_combine(
    ['newKey1', 'newKey2', 'newKey3'],
    array_values(['oldKey1' => 1, 'oldKey2' => 2, 'oldKey3' => 3])
);

This should do the trick as long as you have the same number of values and the same order.

IMO using array_combine, array_merge, even array_intersect_key is overkill. The original code is good enough, and very fast.

Adapting @shawn-k solution, here is more cleaner code using array_walk, it will only replace desired keys, of course you can modify as per your convenience

array_walk($old, function($value,$key)use ($keyReplaceInfoz,&$old){
        $newkey = array_key_exists($key,$keyReplaceInfoz)?$keyReplaceInfoz[$key]:false;
        if($newkey!==false){$old[$newkey] = $value;unset($old[$key]);
        }
    });

    print_r($old);

I just solved this same problem in my own application, but for my application $keyReplaceInfoz acts like the whitelist- if a key is not found, that whole element is removed from the resulting array, while the matching whitelisted keys get translated to the new values.

I suppose you could apply this same algorithm maybe with less total code by clever usage of array_map (http://php.net/manual/en/function.array-map.php), which perhaps another generous reader will do.

function filterOldToAllowedNew($key_to_test){       
    return isset($keyReplaceInfoz[$key_to_test])?$keyReplaceInfoz[$key_to_test]:false;
}   

$newArray = array();

foreach($old as $key => $value){
    $newkey = filterOldToAllowedNew($key);
    if($newkey){
       $newArray[$newkey] = $value;
    }
}

print_r($newArray);

This question is old but since it comes up first on Google I thought I'd add solution.

// Subject
$old = array('foo' => 1, 'baz' => 2, 'bar' => 3));

// Translations    
$tr  = array('foo'=>'FOO', 'bar'=>'BAR');

// Get result
$new = array_combine(preg_replace(array_map(function($s){return "/^$s$/";}, 
           array_keys($tr)),$tr, array_keys($old)), $old);

// Output
print_r($new);

Result:

    
    Array
    (
       [FOO] => 1
       [baz] => 2
       [BAR] => 3
    )

    <?php
$new = array(); 

foreach ($old as $key => $value)
{
     $new[$keyReplaceInfoz][$key] = $value;

}
?>

This the solution i have implemented for the same subject:

/**
 * Replace keys of given array by values of $keys
 * $keys format is [$oldKey=>$newKey]
 *
 * With $filter==true, will remove elements with key not in $keys
 *
 * @param  array   $array
 * @param  array   $keys
 * @param  boolean $filter
 *
 * @return $array
 */
function array_replace_keys(array $array,array $keys,$filter=false)
{
    $newArray=[];
    foreach($array as $key=>$value)
    {
        if(isset($keys[$key]))
        {
            $newArray[$keys[$key]]=$value;
        }
        elseif(!$filter)
        {
            $newArray[$key]=$value;
        }
    }

    return $newArray;
}

This works irrespective of array order & array count. Output order & value will be based on replaceKey.

$replaceKey = array('a' => 'newA', 'b' => 'newB', 'c' => 'newC', 'd' => 'newD', 'e' => 'newE','f'=>'newF');

$array = array(
       'a' => 'blah',
       'd' => array(
                0 => 'want to replace',
                1 => 'yes I want to'
              ),
       'noKey'=>'RESIDUAL',
       'c' => 'amazing',
       'b' => 'key',
       );

$filterKey = array_intersect_key($replaceKey,$array);
$filterarray = array_intersect_key(array_merge($filterKey,$array),$filterKey);

$replaced = array_combine($filterKey,$filterarray);

//output
var_export($replaced);
//array ( 'newA' => 'blah', 'newB' => 'key', 'newC' => 'amazing', 'newD' => array ( 0 => 'want to replace', 1 => 'yes I want to' ) )

If you're looking for a recursive solution to use on a multidimensional array, have a look at the below method. It will replace all keys requested, and leave all other keys alone.

/**
 * Given an array and a set of `old => new` keys,
 * will recursively replace all array keys that
 * are old with their corresponding new value.
 *
 * @param mixed $array
 * @param array $old_to_new_keys
 *
 * @return array
 */
function array_replace_keys($array, array $old_to_new_keys)
{
    if(!is_array($array)){
        return $array;
    }

    $temp_array = [];
    $ak = array_keys($old_to_new_keys);
    $av = array_values($old_to_new_keys);

    foreach($array as $key => $value){
        if(array_search($key, $ak, true) !== false){
            $key = $av[array_search($key, $ak)];
        }

        if(is_array($value)){
            $value = array_replace_keys($value, $old_to_new_keys);
        }

        $temp_array[$key] = $value;
    }

    return $temp_array;
}

Using OP's example array:

$old = array(
       'a' => 'blah',
       'b' => 'key',
       'c' => 'amazing',
       'd' => array(
                0 => 'want to replace',
                1 => 'yes I want to'
              )
       );
$replace = ["a" => "AA", 1 => 11];

var_export(array_replace_keys($old, $replace));

Gives the following output:

array (
  'AA' => 'blah',
  'b' => 'key',
  'c' => 'amazing',
  'd' => 
  array (
    0 => 'want to replace',
    11 => 'yes I want to',
  ),
)

DEMO

Inspired by the following snippet.

This uses @Summoner's example but keeps @Leigh's hint in mind:

$start = microtime();
$array = [ "a" => 1, "b" => 2, "c" => 3 ];

function array_replace_key($array, $oldKey, $newKey) {
    $keys = array_keys($array);
    $idx = array_search($oldKey, $keys);
    array_splice($keys, $idx, 1, $newKey);
    return array_combine($keys, array_values($array));
}

print_r(array_replace_key($array, "b", "z"));