如何合并PHP数组？

$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid", 4);
$result = array_merge($array1, $array2);
print_r($result);

Array
(
    [color] => green
    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => trapezoid
    [4] => 4
)

$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid", 4);
$result = $array1 + $array2;
print_r($result);

Array
(
    [color] => green
    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => trapezoid
    [4] => 4
)

$array1 = array("color" => array("red", "green", "blue"), 2, 4);
$array2 = array("color" => array("yellow", "purple"), "shape" => array("trapezoid", "triangle"));
$result = array_merge_recursive($array1, $array2);
print_r($result);

Array
(
    [color] => Array
        (
            [0] => red
            [1] => green
            [2] => blue
            [3] => yellow
            [4] => purple
        )

    [0] => 2
    [1] => 4
    [shape] => Array
        (
            [0] => trapezoid
            [1] => triangle
        )
)