Multidimensional Array (with some values not sub-arrays) to string?

Question

I am trying to turn a multidimensional array into a patterned string with this array_map function:

function array_to_string($array) {
 return implode("&",array_map(function($a){return implode("~",$a);},$array));
}
$arr = array("hello",array("blue","red"),array("one","three","twenty"),"random");
array_to_string($arr);

Between each array element "&" and between each sub-array element (if it is an array) "~"

Should Output: hello&blue~red&one~three~twenty&random

However this outputs: Warning: implode(): Invalid arguments passed (2) I tried changing the function within the array_map to detect whether the multi-array's value is_array but from my outputs, I don't think that is possible? So essentially, I guess the real question is how can I place a test on the array_map function to see whether or not it is_array

Answer 1

Since $a can be an array or a string, you should check it in your callback function:

function array_to_string($array) {
 return implode("&",
 array_map(function($a) {
 return is_array($a) ? implode("~",$a) : $a;
 }, $array)
 );
}