PHP check if value in array of objects exists more than once

Question

I've this array here with multiple object:

$batches = [
    [
        'id' => 2,
        'number' => 'ABC'
    ],
    [
        'id' => 3,
        'number' => 'ABC'
    ],
    [
        'id' => 4,
        'number' => 'DEF'
    ]
];

Now I need to know if there are any numbers that exists more than once. In this case its ABC.

I've tried using array_sum and array_column but this seems to only work with numbers:

$test = array_sum( array_column( $batches, 'number' ) );

Why would you use array_sum()? They're not numbers, you can't add them. — Barmar
– Barmar, Commented May 4, 2021 at 20:35
And even if they were numbers, how would that tell you if there are duplicates? — Barmar
– Barmar, Commented May 4, 2021 at 20:36
@miken32 I don't think that's right, either. This is looking in a specific key of associative arrays. — Barmar
– Barmar, Commented May 4, 2021 at 20:41

Mr. Jo · Accepted Answer · 2021-05-04 20:48:43Z

2

Use array_count_values() to count the repetitions. Then you can filter this to just the ones with counts more than 1.

$results = array_keys(
    array_filter(array_count_values(array_column($batches, 'number')),
                 static function($count) { return $count > 1; }));

edited May 4, 2021 at 20:48

Mr. Jo

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answered May 4, 2021 at 20:44

Barmar

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5 Comments

Mr. Jo Over a year ago

Awesome! That's what I was looking for! Thanks Barmar :)

Barmar Over a year ago

I'm not sure what the benefit of declaring it static is.

Mr. Jo Over a year ago

Thats just how I learned it so I thought it might be correct. I think this is just a style decision.

Barmar Over a year ago

From the documentation: Anonymous functions may be declared statically. This prevents them from having the current class automatically bound to them. Unless the code is inside a class, it doesn't make any difference.

Mr. Jo Over a year ago

Thanks for the explanation. Now it makes sense.

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