Validate a string of numbers, even if they are in a list separated by commas

validate_int.php

$list_of_ids = '1,2,3,4,5,6';
if ( cg_validate_int( $list_of_ids ) ) {
	echo 'Huzzah! We have valide integers!';
}

/**
 * Allows us to pass either an array of or a single intger and validate that they are integers
 * 
 * @param  int|string $list_of_ids Pass either a single integer or a comma separated list
 *
 * @return bool
 */
function cg_validate_int( $list_of_ids ) {
	// Separate the list and convert the string to an integer
	$ids = array_map( 'intval', explode( ',', $list_of_ids ) );
	
	// Init array
	$results = array();

	// Loop through each and set a string of true or false
	foreach ( $ids as $id ) {
		// If a value was passed that couldn't be converted to an integer, it will result in 0.
		// If that is the case, validation failed, set false as the value then.
		// Other wise, we have a valide integer
		$results[] = ( $id !== 0 ) ? 'true' : 'false';
	}
	
	// Check if any of the values in our array failed validation
	if ( in_array( 'false', $results ) ) {
		return false;
	}
	
	// If everything checked out, then we are good.
	return true;
}

Forked and posted a version that short circuits for efficiency on operating over long lists, and handles the zero by doing a reverse conversion