Online PHP editor | output for D84lS

<?php // define arrays with the same keys - different key order ('4' and '@' are swapped) $array_at = [ '_' => '', 'Y' => '', '0' => '', '+' => '', 'X' => '', 'W' => '', '1' => '', '3' => '', '@' => '', '4' => '', '5' => '', 'P' => '', 'O' => '', 'N' => '', 'M' => '', 'L' => '', 'K' => '', ]; $array_fr = [ '_' => '', 'Y' => '', '0' => '', '+' => '', 'X' => '', 'W' => '', '1' => '', '3' => '', '4' => '', '@' => '', '5' => '', 'P' => '', 'O' => '', 'N' => '', 'M' => '', 'L' => '', 'K' => '', ]; ksort($array_at, SORT_STRING); // sort by key ksort($array_fr, SORT_STRING); // sort by key // expects the same key at the sorted array first position var_dump(array_slice($array_at, 0, 1)); // result: [0 => '''], but only '0' is defined as a key var_dump(array_slice($array_fr, 0, 1)); // result: ['+' => '' ]