Function to sum two arrays in php

arraySum.php

<?php
	/**
	 * Function to sum two arrays
	 *
	 * @param array $a First array to merge
	 * @param array $b Second array to merge which gonna be returned by function
	 * 
	 * @author Orlando Villegas Galán <[email protected]>
	 * @return $b
	 */ 	
	function sumArrays(array $a = [], array $b = []) {
		foreach ($a as $k => $v) {//Iterate along the '$a' array, getting key value pair for every array position
			if(array_key_exists($k, $b)){//Check if '$a' key exist in '$b'
			//If key exist into '$b' array
				if(is_array($v)){//Check if value of key is an array
				//If value is an array
					$b[$k] = sumArrays($b[$k],$v);//The function is called itself recursively
				}else{
					//Otherwise
					$b[$k]+=$v;//Accumulates the '$a' value in '$b' key position
				}
			}else{
				//Otherwise
				$b[$k]=$v; //Create key node in '$b'
			}
		}
		//Return merged '$b'
		return $b;
	}
	
	/** Array declaration **/
	$a = [4,"a" => 3, "b" => ["ba" => 1, "bc" => 2], "c" => ["ca" => 4, "cb" => 3]];
	$b = [5,"a" => 2, "b" => ["ba" => 4, "bc" => 3], "c" => ["ca" => 4]];
	
	print_r(sumArrays($a, $b));
	
	/** Output **/
	/*
	Array
	(
		[0] => 9
		[a] => 5
		[b] => Array
			(
				[ba] => 5
				[bc] => 5
			)

		[c] => Array
			(
				[ca] => 8
				[cb] => 3
			)

	)
	*/
?>