How to determine if a PHP array element is indexed or associative

PHP allows you to mix indexed arrays and associative arrays together. The function below demonstrates how you can determine whether an element is indexed or associative.

// A mixed array
$array = ['indexed', 'foo' => 'bar', 'indexed'];

print_r($array);

/*
Array
(
    [0] => indexed
    [foo] => bar
    [1] => indexed
)
*/

foreach ($array as $key => $value) {

    if (is_int($key) === true) { // Use `(string) ctype_digit($key)` for a looser check

        echo 'indexed' . PHP_EOL; 

    } else {

        echo 'associative' . PHP_EOL; 

    }

}

/*
Output: 

indexed
associative
indexed
*/