Question

I want to check only the value [id] for duplicates, and remove all keys where this “field” [id] is a duplicate.

Example: If I have numbers 1,2,1. I want the result to be 2, not 1,2. And criteria for duplicates is determined only by checking [id], not any other “field”.

Original array:

Array
(
    [0] => Array
        (
            [name] => John
            [id] => 123
            [color] => red
        )

    [1] => Array
        (
            [name] => Paul
            [id] => 958
            [color] => red
        )

    [2] => Array
        (
            [name] => Jennifer
            [id] => 123
            [color] => yellow
        )
)

The result I want:

Array
(
    [0] => Array
        (
            [name] => Paul
            [id] => 958
            [color] => red
        )

)

Answer 1

This should be fairly easy to accomplish with a couple of simple loops:

set_time_limit(0); // Disable time limit to allow enough time to process a large dataset

// $items contains your data

$id_counts = array();
foreach ($items as $item) {
    if (array_key_exists($item['id'], $id_counts)) {
        $id_counts[$item['id']]++;
    } else {
        $id_counts[$item['id']] = 1;
    }
}

for ($i = count($items); $i >= 0; $i--) {
    if ($id_counts[$items[$i]['id']] > 1) {
        array_splice($items, $i, 1);
    }
}

Result:

Array
(
    [0] => Array
        (
            [name] => Paul
            [id] => 958
            [color] => red
        )
)

While there are neater ways to do it, one advantage of this method is you’re only creating new arrays for the list of ids and duplicate ids and the array_splice is removing the duplicates from the original array, so memory usage is kept to a minimum.

Edit: Fixed a bug that meant it sometimes left one behind