如何获取数组特定索引的唯一值？

Question

Here is my sample array

    Array
(
    [0] => Array
        (
            [size] => 7.5 D(M) US
            [price] => $49.99
            [color] => Black Grey
        )

    [1] => Array
        (
            [size] => 8 D(M) US
            [price] => $46.90
            [color] => Black
        )

    [2] => Array
        (
            [size] => 8 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [3] => Array
        (
            [size] => 8.5 D(M) US
            [price] => $46.90
            [color] => Black Grey
        )

    [4] => Array
        (
            [size] => 8.5 4E US
            [price] => $49.99
            [color] => BLACK/MTLC DARK GREY/BLACK
        )

    [5] => Array
        (
            [size] => 9 D(M) US
            [price] => $49.99
            [color] => Black
        )

    [6] => Array
        (
            [size] => 9 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [7] => Array
        (
            [size] => 9.5 D(M) US
            [price] => $49.99
            [color] => Black Grey
        )

    [8] => Array
        (
            [size] => 9.5 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [9] => Array
        (
            [size] => 10 D(M) US
            [price] => $49.99
            [color] => Black
        )

    [10] => Array
        (
            [size] => 10 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [11] => Array
        (
            [size] => 10.5 D(M) US
            [price] => $49.99
            [color] => Black Grey
        )

    [12] => Array
        (
            [size] => 10.5 4E US
            [price] => $49.99
            [color] => BLACK/MTLC DARK GREY/BLACK
        )

    [13] => Array
        (
            [size] => 11 D(M) US
            [price] => $54.90
            [color] => Black
        )

    [14] => Array
        (
            [size] => 11 D(M) US
            [price] => $57.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [15] => Array
        (
            [size] => 11 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [16] => Array
        (
            [size] => 11.5 D(M) US
            [price] => $47.84
            [color] => Black Grey
        )

    [17] => Array
        (
            [size] => 12 D(M) US
            [price] => $50.90
            [color] => Black
        )

    [18] => Array
        (
            [size] => 12 4E US
            [price] => $75.00
            [color] => Black/Metallic Dark Grey/Black
        )

    [19] => Array
        (
            [size] => 13 D(M) US
            [price] => $58.59
            [color] => Black
        )

    [20] => Array
        (
            [size] => 13 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [21] => Array
        (
            [size] => 14 D(M) US
            [price] => $54.99
            [color] => Black
        )

    [22] => Array
        (
            [size] => 14 4E US
            [price] => $49.99
            [color] => Black/Metallic Dark Grey/Black
        )

    [23] => Array
        (
            [size] => 15 D(M) US
            [price] => $54.99
            [color] => Black
        )

)

And I want to happen is that to get only the unique value of "color"

echo '<select>';
    foreach($store as $item){
        echo '<option>'.$item['color'].'</option>';
    }
    echo '</select>';

And here's I want to display it..

Answer 1

<?php
$items = Array
(
    Array
    (
        'size' => '7.5 D(M) US',
        'price' => '$49.99',
        'color' => 'Black Grey',
    ),
    Array
    (
        'size' => '8 D(M) US',
        'price' => '$46.90',
        'color' => 'Black'
    )
);


$colors = array();
foreach ($items as $item) {
    $colors[] = $item['color'];
}
$colors = array_unique($colors);
var_dump($colors);