How to remove duplicate elements in a multidimensional array?

Question

PHP

Hello. I have the following problem. I have an array like this:

Array
(
    [0] => Array
        (
            [id_city] => 2096
            [ip_start] => 2.60.0.0
            [ip_end] => 2.60.255.255
            [city] => Омск
        )

    [1] => Array
        (
            [id_city] => 676
            [ip_start] => 2.61.0.0
            [ip_end] => 2.61.255.255
            [city] => Абакан
        )

    [2] => Array
        (
            [id_city] => 1706
            [ip_start] => 2.62.0.0
            [ip_end] => 2.62.255.255
            [city] => Кемерово
        )

    [3] => Array
        (
            [id_city] => 1428
            [ip_start] => 2.63.0.0
            [ip_end] => 2.63.127.255
            [city] => Красноярск
        )
...

The city field may be repeated in some elements of the array. As far as I understand array_unique()it won't work here. Can you please tell me how to remove all repetitions and leave only unique array elements in the city field?
Thanks in advance to all who respond.

Answer 1

// получаем уникальные ключи
$uniqueKeys = array_keys(
    array_unique(
        array_map(function($item) {
            return $item['city'];
        }, $array)
    )
);
// извлекаем в новый массив те ключи, которые были уникальными
$uniqueArray = array_filter($array, function($itemKey) {
    return in_array($itemKey, $uniqueKeys);
}, ARRAY_FILTER_USE_KEY);