find repeated values in multidimensional array

Question

Given this array:

Array
(
    [0] => Array
        (
            [id] => 3
            [name] => aaa
        )

    [1] => Array
        (
            [id] => 2
            [name] => bbb
        )

    [2] => Array
        (
            [id] => 3
            [name] => aaa
        )

    [3] => Array
        (
            [id] => 1
            [name] => ccc
        )

    [4] => Array
        (
            [id] => 3
            [name] => aaa
        )        
)

How can I check if a value for a specific key is used more than once and return the key?

For example, I want to know which keys have the repeated "id" sub key. In this case id = 3 appears more than once so the result would be

Array
(
    [0] => 2
    [1] => 4
)

Notice that index 0 is not included because it's not actually repeated since is the first to appear.

Create a second array. Loop through the first. For each, check if the id is in the second array. If it is not, add it. If it is, echo the index of the current item (or add that index to a 3rd array to create the array you're showing) — Patrick Q
– Patrick Q, Commented May 11, 2018 at 17:02
What if id 1 was also repeated, what would the result look like? How would you differentiate between 1 and 3? — AbraCadaver
– AbraCadaver, Commented May 11, 2018 at 17:10
@AbraCadaver Then it's repeated index would be added to the final result — Matías Cánepa
– Matías Cánepa, Commented May 11, 2018 at 17:15
So from your example array, if array [1] was id 1 and array [3] was id 1 the result would just be 2,3,4? — AbraCadaver
– AbraCadaver, Commented May 11, 2018 at 17:16

Don't Panic · Accepted Answer · 2018-05-11 17:36:03Z

3

Iterate your array and add the id of each item to an array. If you encounter an id that's already in the array, add its key to an array of duplicates.

foreach ($array as $key => $item) {
    if (isset($ids[$item['id']])) {
        $duplicates[] = $key;
    } else {
        $ids[$item['id']] = true;
    }
}

I prefer to use the unique attribute (id in the case) as the key (like $ids[$item['id']]) instead of the value so it can be looked up with isset rather than in_array.

edited May 11, 2018 at 17:36

answered May 11, 2018 at 17:16

Don't Panic

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3 Comments

jvk Over a year ago

i don't why you are using isset($ids[$item['id']]

Don't Panic Over a year ago

@whoami to check if the id of the current item has already been added to the array of ids, meaning the current item is a duplicate.

jvk Over a year ago

what a brilliant answer, i am daily working on arrays, still panic on array, is nice way to learn array

Lawrence Cherone · Accepted Answer · 2018-05-11 17:19:43Z

2

If you are trying to find the repeated values, rather than eliminate them, you could achieve this by combining array_column array_diff_uassoc and array_unique to return an array of the repeated values while maintaining the indexes:

$ids = array_column($originalArray, 'id');
$uniqueIds = array_unique($ids);
$repeatedValuesArray = array_diff_uassoc($ids, $uniqueIds, "key_compare_func");

edited May 11, 2018 at 17:19

Lawrence Cherone

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answered May 11, 2018 at 17:09

mtr.web

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1 Comment

mtr.web Over a year ago

@MatíasCánepa the edit should work, but an even simpler version would be array_diff_assoc($ids, $uniqueIds); The answer just provides an additional index check.

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