使用允许的键数组按其键过滤数组 [英] Filter array by its keys using an array of allowed keys

问题描述

array_filter()中的回调函数 只传入数组的值，而不是键.

The callback function in array_filter() only passes in the array's values, not the keys.

如果我有:

$my_array = array("foo" => 1, "hello" => "world");

$allowed = array("foo", "bar");

删除 $my_array 中所有不在 $allowed 数组中的键的最佳方法是什么?

What's the best way to delete all keys in $my_array that are not in the $allowed array?

期望的输出:

$my_array = array("foo" => 1);

推荐答案

PHP 5.6 为 array_filter() 引入了第三个参数，flag，可以设置为 ARRAY_FILTER_USE_KEY 改为按键过滤价值:

PHP 5.6 introduced a third parameter to array_filter(), flag, that you can set to ARRAY_FILTER_USE_KEY to filter by key instead of value:

$my_array = ['foo' => 1, 'hello' => 'world'];
$allowed  = ['foo', 'bar'];
$filtered = array_filter(
    $my_array,
    function ($key) use ($allowed) {
        return in_array($key, $allowed);
    },
    ARRAY_FILTER_USE_KEY
);

由于 PHP 7.4 引入了箭头函数，我们可以让它更简洁:

Since PHP 7.4 introduced arrow functions we can make this more succinct:

$my_array = ['foo' => 1, 'hello' => 'world'];
$allowed  = ['foo', 'bar'];
$filtered = array_filter(
    $my_array,
    fn ($key) => in_array($key, $allowed),
    ARRAY_FILTER_USE_KEY
);

显然这不如 array_intersect_key($my_array, array_flip($allowed))，但它确实提供了对密钥执行任意测试的额外灵活性，例如$allowed 可以包含正则表达式模式而不是纯字符串.

Clearly this isn't as elegant as array_intersect_key($my_array, array_flip($allowed)), but it does offer the additional flexibility of performing an arbitrary test against the key, e.g. $allowed could contain regex patterns instead of plain strings.

您也可以使用 ARRAY_FILTER_USE_BOTH 将值和键都传递给您的过滤器函数.这是一个基于第一个的人为示例，但请注意，我不建议以这种方式使用 $allowed 编码过滤规则:

You can also use ARRAY_FILTER_USE_BOTH to have both the value and the key passed to your filter function. Here's a contrived example based upon the first, but note that I'd not recommend encoding filtering rules using $allowed this way:

$my_array = ['foo' => 1, 'bar' => 'baz', 'hello' => 'wld'];
$allowed  = ['foo' => true, 'bar' => true, 'hello' => 'world'];
$filtered = array_filter(
    $my_array,
    // N.b. it's ($val, $key) not ($key, $val):
    fn ($val, $key) => isset($allowed[$key]) && (
        $allowed[$key] === true || $allowed[$key] === $val
    ),
    ARRAY_FILTER_USE_BOTH
); // ['foo' => 1, 'bar' => 'baz']

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