<?php
$yes = array('this', 'is', 'an array');
echo is_array($yes) ? 'Array' : 'not an Array';
echo "\n";
$no = 'this is a string';
echo is_array($no) ? 'Array' : 'not an Array';
?>
$id = 1;
$age = 2;
$sort = "id"; // or "age";
$Key = $$sort;
$arr = array($Key => 'string');
print_r($arr);