PHP：将指定的子数组合并到新数组中？

Question

我正在使用 PHP，我需要一个函数，它将二维数组中用户指定的子数组合并到一个新数组中，例如

$arr = [
    "sub_1" => [ "a", "b" ],
    "sub_2" => [ "c", "d" ],
    "sub_3" => [ "e", "f" ],
    "sub_a" => [ 1, 2, 3 ],
    "sub_b" => [ 4, 5, 6 ],
    "sub_c" => [ 7, 8, 9 ]
];

merge_subs( $arr, [ "sub_1", "sub_2", "sub_3" ] );
// should return: [ "a", "b", "c", "d", "e", "f" ]

merge_subs( $arr, [ "sub_a", "sub_b", "sub_c" ] );
// should return: [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

最有效的方法是什么？

编辑：

这是我尝试过的，但它不起作用，所以我显然做错了什么。

function merge_subs( $arr, $subs ){
    $new = [];
    foreach( $subs as $sub ){
        array_push( $new, $arr[$sub] );
    }
    return array_merge( $new );
}

编辑 2：

我意识到我遗漏了省略号，现在我可以使用它了。无论如何，我想知道是否有更好的方法来实现这一点。

Answer 1

您正在寻找$new = array_merge($new, $arr[$sub]);

<?php
$arr = [
    "sub_1" => [ "a", "b" ],
    "sub_2" => [ "c", "d" ],
    "sub_3" => [ "e", "f" ],
    "sub_a" => [ 1, 2, 3 ],
    "sub_b" => [ 4, 5, 6 ],
    "sub_c" => [ 7, 8, 9 ]
];

function merge_subs( $arr, $subs ){
    $new = [];
    foreach( $subs as $sub ){
        $new = array_merge($new, $arr[$sub]);
    }
    return $new;
}


print_r(merge_subs( $arr, [ "sub_1", "sub_2", "sub_3" ] ));
// should return: [ "a", "b", "c", "d", "e", "f" ]

print_r(merge_subs( $arr, [ "sub_a", "sub_b", "sub_c" ] ));

结果：

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
    [5] => f
)
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
)

Answer 2

接受的答案通过获取一组键并循环来满足您的要求，但为什么呢？只需指定要合并的键：

$result = array_merge($arr[ "sub_1"], $arr["sub_2"], $arr["sub_3"]);

比循环更复杂，但为了好玩：

function merge_subs($array, $keys) {
    return array_merge(...array_values(array_intersect_key($array, array_flip($keys))));
}

• 从$arr 中获取相同$keys 传递的元素array_intersect_key
• 获取值array_values
• 像在第一个解包示例中那样使用... 合并它们