Return array keys that match the pattern.

preg_grep_keys.php

<?php

function preg_grep_keys( $pattern, $input, $flags = 0 )
{
    $keys = preg_grep( $pattern, array_keys( $input ), $flags );
    $vals = array();
    foreach ( $keys as $key )
    {
        $vals[$key] = $input[$key];
    }
    return $vals;
}

?>

Retrieved from this comment on the php preg_grep manual page.