2d array - group by value and sum up same keys' values

Question

Hello and thanks for taking the time to look at my question.

My current problem is that, I have the following array ( $topics_percentage ):

Array
(
    [0] => Array
        (
            [id] => 8989
            [cat] => Category 1
            [completed] => 0
        )

    [1] => Array
        (
            [id] => 8919
            [cat] => Category 2
            [completed] => 1
        )

    [2] => Array
        (
            [id] => 8913
            [cat] => Category 2
            [completed] => 1
        )

    [3] => Array
        (
            [id] => 8947
            [cat] => Category 1
            [completed] => 1
        )

    [4] => Array
        (
            [id] => 8949
            [cat] => Category 3
            [completed] => 1
        )

)

What I need to get, is something like the following example:

Array
(
    [Category 1] => Array
        (
            [noncompleted] => 1
            [completed] => 1
        )

    [Category 2] => Array
        (
            [completed] => 2
        )

    [Category 3] => Array
        (
            [completed] => 1
        )

)

What I've tried so far is this:

$class_array = [];

foreach ($topics_percentage as $v) {

    $complete = $v['completed'];

    $class_array[$v['cat']][] =
        ($complete == 0 ? 'noncompleted' : 'completed');
}

Which returns the following:

Array
(
    [Category 1] => Array
        (
            [0] => noncompleted
            [1] => completed
        )

    [Category 2] => Array
        (
            [0] => completed
            [1] => completed
        )

    [Category 3] => Array
        (
            [0] => completed
        )

)

I'm weak when it comes to arrays, and can't figure out the logic.

Thanks in advance.

Answer 1

Try this:

$values = array_unique(array_map(
    function ($v) { return $v['cat']; },
    $array
));

$result = array();
foreach ($values as $val) {
    $flt = array_filter($array, function ($v) use ($val) {
        return $v['cat'] == $val;
    });
    $cnt = count(array_filter($array, function ($v) use ($val) {
        return $v['completed'];
    }));
    $result[$val] = array(
        'completed' => $cnt,
        'noncompleted' => count($flt) - $cnt
    );
}

Answer 2

Try this:

    foreach ($topics_percentage as $v) {

        $complete = $v['completed'];

        if ($complete == 1) {
            $class_array[$v['cat']]['completed']++;
        } else {
            $class_array[$v['cat']]['uncompleted']++;
        }
    }

You should, of course, preinitialize the array before you count up values, but the basic idea is to use array cells as numeric values to be added or substracted from.