PHP splitting array into two arrays based on value

This should do the trick:

$myArray = array('item1', 'item2hidden', 'item3', 'item4', 'item5hidden');
$secondaryArray = array();

foreach ($myArray as $key => $value) {
    if (strpos($value, "hidden") !== false) {
        $secondaryArray[] = $value;
        unset($myArray[$key]);
    }
}

It moves all the entries that contain "hidden" from the $myArray to $secondaryArray.

Note: It's case sensitive

You can use array_filter() function:

$myArray = array('item1', 'item2hidden', 'item3', 'item4', 'item5hidden');

$arr1 = array_filter($myArray, function($v) { return strpos($v, 'hidden') === false; });
$arr2 = array_diff($myArray, $arr1);