php recursive array search for needle. returns path of keys to value or false

in_array_multi.php

<?php
// This function searches for needle inside of multidimensional array haystack
// Returns the path to the found element or false
function in_array_multi( $needle, array $haystack ) {
	if ( ! is_array( $haystack ) ) return false;

	foreach ( $haystack as $key => $value ) {
		if ( $value == $needle ) {
			return $key;
		} else if ( is_array( $value ) ) {
			// multi search
			$key_result = in_array_multi( $needle, $value );
			if ( $key_result !== false ) {
				return $key . '_' . $key_result;
			}
		}
	}

	return false;
}

// Test
$test = [ 
	'SUBJECT' => [
		'STD',
		'STK',
		'JMK',
		3 => [
			'TEST'
		]
	], 
	'COUNTRY' => [
		'USA'
	] 
];

$key_path = in_array_multi( 'TEST', $test );
if ( $key_path !== false ) {
  echo $key_path;
}

// Outputs:
// SUBJECT_3_0
// $test['SUBJECT'][3][0] === 'TEST'