无法过滤多维关联数组：如何提取指定字段生成新数组？

我通过GET请求访问API，先用以下代码筛选出schedule.type为weekly的元素：

$results = array_filter($body, function($item) {
    if(!isset($item['schedule']['type']))
        return false;
    return $item['schedule']['type'] == "weekly";
});

返回的数组结构精简版如下：

array (
    6 => 
        array (
            'foo' => 'other fields x 100',
            'title' => 'Episode 1 Title',
            'automatically_title_stream' => false,
            'stream_title' => 'Episode 1 Title',
            'stream_description' => 'Join us each afternoon for real-time market analysis and live futures trading in this interactive live stream event.',
            'rtmp_link' => 'rtmp://rtmp-global.cloud.vimeo.com/live',
            'rtmps_link' => 'rtmps://rtmp-global.cloud.vimeo.com:443/live',
            'stream_key' => '97deb5f6-9bef-4e1c-91f8-d39f72657290',
            'schedule' => 
                array (
                  'type' => 'weekly',
                  'start_time' => NULL,
                  'daily_time' => '19:15:00Z',
                  'scheduled_time' => NULL,
                  'weekdays' => 
                      array (
                        0 => 1,
                        1 => 2,
                        2 => 3,
                        3 => 4,
                        4 => 5,
                     ),
                ),
            ),
    7 => 
          array (
            'foo' => 'other fields x 100',
            'title' => 'Episode 2 Title',
            'automatically_title_stream' => false,
            'stream_title' => 'Bars Closing',
            'stream_description' => 'Join us each afternoon for real-time market analysis and live futures trading in this interactive live stream event.',
            'rtmp_link' => 'rtmp://rtmp-global.cloud.vimeo.com/live',
            'rtmps_link' => 'rtmps://rtmp-global.cloud.vimeo.com:443/live',
            'stream_key' => '97deb5f6-9bef-4e1c-91f8-d39f72657290',
            'schedule' => 
            array (
                'type' => 'weekly',
                'start_time' => NULL,
                'daily_time' => '19:15:00Z',
                'scheduled_time' => NULL,
                'weekdays' => 
                      array (
                        0 => 1,
                        1 => 2,
                        2 => 3,
                        3 => 4,
                        4 => 5,
            ),
        ),
       )
     )

这段筛选代码能正常工作，但返回的数组过于庞大（超过56000行），我只需要保留title、stream_description和weekdays字段。尝试用以下代码处理时得到空数组：

$allowed  = ['title', 'stream_description', 'weekdays'];
$filtered = array_filter(
    $results,
    fn ($key) => in_array($key, $allowed),
    ARRAY_FILTER_USE_KEY
);

请问如何从指定键列表生成新数组，剔除不必要的数据？

问题原因 #

你用array_filter加ARRAY_FILTER_USE_KEY是在过滤外层数组的键（也就是示例中的6、7这些索引），但实际需求是过滤每个子数组里的字段，逻辑不匹配导致返回空数组。

解决方案 #

1. 针对当前需求的快速实现 #

遍历筛选后的$results数组，提取顶层指定字段，并单独处理嵌套的weekdays：

$allowed = ['title', 'stream_description'];
$final = [];

foreach ($results as $key => $item) {
    // 提取顶层允许的字段
    $entry = array_intersect_key($item, array_flip($allowed));
    // 加入嵌套的weekdays字段，兼容字段不存在的情况
    $entry['weekdays'] = $item['schedule']['weekdays'] ?? [];
    $final[$key] = $entry;
}

2. 简洁写法（PHP 7.4+） #

用array_map结合匿名函数，直观处理固定字段：

$final = array_map(function($item) {
    return [
        'title' => $item['title'],
        'stream_description' => $item['stream_description'],
        'weekdays' => $item['schedule']['weekdays'] ?? []
    ];
}, $results);

3. 通用深层字段提取函数（适配复杂数组） #

如果需要处理多层嵌套、字段不固定的复杂数组，可以封装一个通用函数：

function extractArrayFields(array $sourceData, array $fieldMap) {
    $result = [];
    foreach ($sourceData as $key => $item) {
        $entry = [];
        foreach ($fieldMap as $alias => $path) {
            // 支持两种格式：直接写字段名，或用点分隔嵌套路径
            $segments = is_string($path) ? explode('.', $path) : $path;
            $currentValue = $item;
            
            foreach ($segments as $segment) {
                if (!isset($currentValue[$segment])) {
                    $currentValue = null;
                    break;
                }
                $currentValue = $currentValue[$segment];
            }
            
            if ($currentValue !== null) {
                $entry[is_string($alias) ? $alias : end($segments)] = $currentValue;
            }
        }
        $result[$key] = $entry;
    }
    return $result;
}

// 使用示例：指定需要的字段，嵌套字段用点分隔
$fieldMap = [
    'title',
    'stream_description',
    'weekdays' => 'schedule.weekdays'
];

$final = extractArrayFields($results, $fieldMap);

内容的提问来源于stack exchange，提问作者Dirty Bird Design