array_unique for multidimensional array

array_unique removes duplicates from only flattened one dimensional array. But still it can be used in a multi-dimensional array with a small work-around.

Scenario 1: Remove duplicates from array comparing all keys and values in array

Consider this array:

Array
(
    [0] => Array
        (
            [id] => 1
            [value] => 111
        )

    [1] => Array
        (
            [id] => 2
            [value] => 222
        )

    [2] => Array
        (
            [id] => 3
            [value] => 333
        )

    [3] => Array
        (
            [id] => 1
            [value] => 111
        )

)

It can be found that both index 1 and 3 are same. It can removed directly with array_unique using SORT_REGULAR

print_r(array_unique($array, SORT_REGULAR));

This produces:

Array
(
    [0] => Array
        (
            [id] => 1
            [value] => 111
        )

    [1] => Array
        (
            [id] => 2
            [value] => 222
        )

    [2] => Array
        (
            [id] => 3
            [value] => 333
        )

)

---

Scenario 2: Remove duplicates from array comparing a specific key 

Now consider the same array but id  of 3rd index is different:

Array
(
    [0] => Array
        (
            [id] => 1
            [value] => 111
        )

    [1] => Array
        (
            [id] => 2
            [value] => 222
        )

    [2] => Array
        (
            [id] => 3
            [value] => 333
        )

    [3] => Array
        (
            [id] => 4
            [value] => 111
        )

)

Now, index 1 and 3 are not same since id is different. But if you still want to remove duplicated value 111. You can use like this:

$tempArr = array_unique(array_column($array, 'value'));
print_r(array_intersect_key($array, $tempArr));

This produces:

Array
(
    [0] => Array
        (
            [id] => 1
            [value] => 111
        )

    [1] => Array
        (
            [id] => 2
            [value] => 222
        )

    [2] => Array
        (
            [id] => 3
            [value] => 333
        )

)

Explanation:

1.  array_unique – works only with single dimensional array.
2. Hence, convert the multidimensional array to single dimensional with required column only using array_column. Here, with just value. This should give array like:

   Array
   (
       [0] => 111
       [1] => 222
       [2] => 333
       [3] => 111
   )

3. Now, applying array_unique is easy in this that results:

   Array
   (
       [0] => 111
       [1] => 222
       [2] => 333
   )

4. Rebuild the array, from single to multidimensional using the array_intersect_key that computes intersection using keys for comparison which results in the desired array.

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