翻转关联数组并将新值存储在子数组中，以防止丢失重复的值

Question

我有一个平面关联数组，它可能包含重复的值。

Array (
    [for-juniors] => product_category 
    [for-men] => product_category
    [coats] => product_category
    [for-women] => product_category
    [7-diamonds] => brand
) 

我需要重新构造数据以将原始值存储为新键，并将原始键推入与新键关联的子数组中。

array(
    'product_category' => array(
        'for-juniors',
        'for-men',
        'coats',
        'for-women'
    ),
    'brand' => array(
        '7-diamonds'
    )
);

Answer 1

$grouped = array();
foreach ($input as $choice => $group) {
    $grouped[$group][] = $choice;
}

var_dump($grouped);

Answer 2

这样就可以了：

function array_flip_safe(array $array) : array
{
    return array_reduce(array_keys($array), function ($carry, $key) use (&$array) {
        $carry[$array[$key]] ??= []; // PHP 7.0 - ^7.3: $carry[$array[$key]] = $carry[$array[$key]] ?? [];
        $carry[$array[$key]][] = $key;
        return $carry;
    }, []);
}

如果数组不存在，该回调将创建一个空数组。然后将当前迭代的$key ($value of array_keys($array))附加到该数组。

为了更好地理解，这里有一个例子：

$businessHours = [
    'mo' => '13:00 - 16:00',
    'tu' => '8:00 - 12:00',
    'we' => '13:00 - 16:00',
    'th' => '8:00 - 12:00',
    'fr' => '13:00 - 16:00',
    'sa' => '',
    'su' => '',
];

$flipped = array_flip_safe($businessHours);

ray($flipped); (或var_dump、var_export等)输出：

array:3 [▼
  "13:00 - 16:00" => array:3 [▼
    0 => "mo"
    1 => "we"
    2 => "fr"
  ]
  "8:00 - 12:00" => array:2 [▼
    0 => "tu"
    1 => "th"
  ]
  "" => array:2 [▼
    0 => "sa"
    1 => "su"
  ]
]

请注意，内部数组的值的顺序与原始数组的键的顺序相同。