PHP: Function to group array of objects by value

Question

I am working with a multi-dimensional array. How can I remove duplicates by value? In the following array, [0], [2] and [5] have the same [ID]. Is there a function that will remove any duplicate arrays based on a particular value? In this case, I would like to remove array [2] and array [5], as they have the same [ID] as array [0].

Thank you for any information you may have.

        Array
(
    [0] => stdClass Object
        (
            [d] => 2010-10-18 03:30:04
            [ID] => 9
        )

    [1] => stdClass Object
        (
            [d] => 2010-10-18 03:30:20
            [ID] => 4
        )

    [2] => stdClass Object
        (
            [d] => 2010-11-03 16:46:34
            [ID] => 9
        )

    [3] => stdClass Object
        (
            [d] => 2010-11-02 03:19:14
            [ID] => 1
        )

    [4] => stdClass Object
        (
            [d] => 2010-05-12 04:57:34
            [ID] => 2
        )    

    [5] => stdClass Object
        (
            [d] => 2010-05-10 05:24:15
            [ID] => 9
        )

)

Answer 1

One way to do it: ($old_array is your array, and $new_array will contain the new one, dupes removed, keyed by that ID)

$new_array = array();
foreach ($old_array as $item)
  if (!array_key_exists($item->ID, $new_array))
    $new_array[$item->ID] = $item;

(I haven't tested this, but it should work)