Group multidimensional arrays by key

Question

I'm stuck on this problem and I hope someone can help me on that. I have an array which I want to group by a specific key. The only problem is that I want to have a new array whenever the value of the key changes during the loop. Here is an example of the array.

Array
(
    [0] => Array
        (
            [id] => 972
            [user_id] => 2
            [user_field_48] => 1
            [project] => 100 — NLO
            [duration] => 1:00
            [grouped_by] => 1
        )

    [1] => Array
        (
            [id] => 644
            [user_id] => 2
            [user_field_48] => 4
            [project] => 123 — QHV
            [duration] => 15:00
            [grouped_by] => 4
        )

    [2] => Array
        (
            [id] => 631
            [user_id] => 2
            [user_field_48] => 4
            [project] => 
            [duration] => -5:00
            [grouped_by] => 4
        )

    [3] => Array
        (
            [id] => 630
            [user_id] => 2
            [user_field_48] => 1
            [project] => 
            [duration] => 22:00
            [grouped_by] => 1
        )

    [4] => Array
        (
            [id] => 971
            [user_id] => 2
            [user_field_48] => 1
            [project] => 100 — NLO
            [duration] => 1:00
            [grouped_by] => 1
        )

    [5] => Array
        (
            [id] => 973
            [user_id] => 2
            [user_field_48] => 1
            [project] => 100 — NLO
            [duration] => 1:00
            [grouped_by] => 1
        )

    [6] => Array
        (
            [id] => 974
            [user_id] => 2
            [user_field_48] => 1
            [project] => 100 — NLO
            [duration] => 1:00
            [grouped_by] => 1
        )

)

I did

foreach($report_items as $item)
{
    $groupedItems[$item['grouped_by']][] = $item;
}

and I got

What I'm actually looking for is something like this, where the arrays are separated during the loop and a suffix is added to the key whenever the value changes.

I'm not really aware of a simple way to solve this, so I would appreciate any help. Thank you!

Hi Nick, it is the first array with the key 4, so it may get a suffix of ".1" for example. It is just a way to make sure that the key is unique. — ntsu, Mar 04 '22 at 01:13
Does this answer your question? [How to group a multidimensional array by a particular subarray value?](https://stackoverflow.com/questions/2189626/how-to-group-a-multidimensional-array-by-a-particular-subarray-value) — Ainz, Mar 04 '22 at 02:08
Can you please present your sample input data in the form of a `var_export` or as JSON? Then people have something they can work with directly by copy&pasting it, the above print_r output does not allow for that. — CBroe, Mar 04 '22 at 07:43
You will have to watch when the `grouped_by` changes between the current item and the previous one. In that case you know that you are done with one "sequence", and that you will have to increase the "sub-index" then next time you encounter the same grouped_by value again. — CBroe, Mar 04 '22 at 07:45

CBroe · Accepted Answer · 2022-03-04T10:26:31.793

Not going to bother to recreate your full array here, I am using a reduced version with just the id and the grouped_by value, but the principle is of course exactly the same if you do it with your "full" array.

I am using a counter array to keep track of which "iteration" of a specific group we are currently dealing with. In classic control break implementation logic, I am comparing the grouped_by of the current record, with that of the previous one - if those differ, then the counter for this grouped_by value has to be incremented by 1. And then, I am simply creating the array key to use, by combining the grouped_by value, and the current count for it.

$data = [['id' => 972, 'grouped_by' => 1], ['id' => 664, 'grouped_by' => 4], ['id' => 631, 'grouped_by' => 4], ['id' => 630, 'grouped_by' => 1], ['id' => 971, 'grouped_by' => 1], ['id' => 973, 'grouped_by' => 1], ['id' => 974, 'grouped_by' => 1]];

$grouped_result = $grouped_by_counts = [];
$previous_grouped_by = null; // a value that will never occur in the data

foreach($data as $datum) {
    if($datum['grouped_by'] !== $previous_grouped_by) {
        $grouped_by_counts[$datum['grouped_by']] =
          isset($grouped_by_counts[$datum['grouped_by']]) ? 
          $grouped_by_counts[$datum['grouped_by']] + 1 : 1;
    }
    $grouped_result[
      $datum['grouped_by'].'.'.$grouped_by_counts[$datum['grouped_by']]
    ][] = $datum;
    $previous_grouped_by = $datum['grouped_by'];
}

print_r($grouped_result);

Live example: https://3v4l.org/odtie

Group multidimensional arrays by key

1 Answers1