array(2) {
  ["a1"]=>
  array(3) {
    ["x"]=>
    string(1) "y"
    [0]=>
    int(1)
    [1]=>
    int(2)
  }
  ["a2"]=>
  array(3) {
    ["x"]=>
    string(1) "y"
    [0]=>
    int(3)
    [1]=>
    int(4)
  }
}