PHP: How do I combine multiple associative arrays into a multidimensional array?

Question

Consider three associative arrays in php:

$a1 = array(
"a" => "1",
"b" => "2",
"c" => "3"
);

$a2 = array(
"d" => "4",
"e" => "5",
"f" => "6"
);

$a3 = array(
"g" => "7",
"h" => "8",
"i" => "9"
);

How would you efficiently combine these into a multidimensional array as follows:

$result = array(
"1" => array("4","7"),
"2" => array("5","8"),
"3" => array("6","9")
);

Thanks in advance!

Answer 1

Very similar to a couple of questions I answered last night:

$a1 = array(
"a" => "1",
"b" => "2",
"c" => "3"
);

$a2 = array(
"d" => "4",
"e" => "5",
"f" => "6"
);

$a3 = array(
"g" => "7",
"h" => "8",
"i" => "9"
);

$x = array_combine(
    $a1,
    call_user_func_array('array_map', [null, $a2, $a3])
);
var_dump($x);