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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
        )

)
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FYI, you keep using the term "key", but you area actually referring to a "value", not a "key". The [0], [2], and [5] you mention are keys. The [ID] is also a key. The 9 that each of these ID's contains are all values. – Matt Huggins Dec 1 '10 at 22:28
thanks, i have modified the language of the question. – superUntitled Dec 1 '10 at 22:42
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4 Answers

up vote 3 down vote accepted

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)

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up vote 0 down vote

I think it would be easiest to loop through and construct a new array. In the loop, use array_key_exists() to determine if the ID already exists in the new array, and if not, append an element.

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up vote 0 down vote

It is not a multidimensional array, it is an array of objects. You can just loop over it (this example changes the array in place):

$ids = array();

forach($array as $key=>$obj) {
    if(isset($ids[$obj->ID])) {//did we already encounter an object with this ID?
        unset($array[$key]); // if yes, delete this object
    }
    else {
        $ids[$obj->ID] = 1; // if not, add ID to processed IDs
    }
}

You can also create a new array and add the objects to the new array.

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up vote 0 down vote 
foreach ($array as $element) {
    foreach ($array as &$element2) {
        if ($element2->ID == $element->ID && $element2 != $element) {
            unset($element2);
        }
    }
}

Note the loop-by-reference in the second foreach.

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