[PHP] Merge N arrays AND sum numeric values of identical keys

array_merge_recursive_numeric()

<?php 
/**
 * array_merge_recursive_numeric function.  Merges N arrays into one array AND sums the values of identical keys.
 * WARNING: If keys have values of different types, the latter values replace the previous ones.
 * 
 * Example:
 * 
 * $a = array( "A" => "bob", "sum" => 10, "C" => array("x","y","z" => 50) );
 * $b = array( "A" => "max", "sum" => 12, "C" => array("x","y","z" => 45) );
 * $c = array( "A" => "tom", "sum" =>  8, "C" => array("x","y","z" => 50, "w" => 1) );
 * 
 * print_r(array_merge_recursive_numeric($a,$b,$c));
 * 
 * Result:
 * 
 * Array
 * (
 *    [A] => tom
 *    [sum] => 18
 *    [C] => Array
 *       (
 *          [0] => x
 *          [1] => y
 *          [z] => 100
 *          [w] => 1
 *      )
 * )
 * 
 * Source:  https://gist.github.com/Nickology/f700e319cbafab5eaedc
 * @params N arrays (all parameters must be arrays)
 * @author Nick Jouannem <nick@nickology.com>
 * @access public
 * @return void
 */
function array_merge_recursive_numeric() {
	
	// Gather all arrays
	$arrays = func_get_args();
	
	// If there's only one array, it's already merged
	if (count($arrays)==1) {
		return $arrays[0];
	}
	
	// Remove any items in $arrays that are NOT arrays
	foreach($arrays as $key => $array) {
		if (!is_array($array)) {
			unset($arrays[$key]);
		}
	}
	
	// We start by setting the first array as our final array.
	// We will merge all other arrays with this one.
	$final = array_shift($arrays);
	
	foreach($arrays as $b) {
	
		foreach($final as $key => $value) {
			
			// If $key does not exist in $b, then it is unique and can be safely merged
			if (!isset($b[$key])) {
				
				$final[$key] = $value;
				
			} else {
				
				// If $key is present in $b, then we need to merge and sum numeric values in both
				if ( is_numeric($value) && is_numeric($b[$key]) ) {
					// If both values for these keys are numeric, we sum them
					$final[$key] = $value + $b[$key];
				} else if (is_array($value) && is_array($b[$key])) {
					// If both values are arrays, we recursively call ourself
					$final[$key] = array_merge_recursive_numeric($value, $b[$key]);
				} else {
					// If both keys exist but differ in type, then we cannot merge them.
					// In this scenario, we will $b's value for $key is used
					$final[$key] = $b[$key];
				}
				
			}
			
		}
	
		// Finally, we need to merge any keys that exist only in $b
		foreach($b as $key => $value) {
			if (!isset($final[$key])) {
				$final[$key] = $value;
			}
		}
		
	}
	
	return $final;
	
}

?>

Thanks for great job! I think return type should be array instead of void.