How to iterate multidimensional array data and sum some values ​to return a grouped array

Question

What's the simplest way and uses less computing power to check if a multidimensional array has some equal values in the sub keys and, if is in this way, make the sum of that?

Look at the input. It's something like this:

$array[] = ['number' => 1, 'values' => ['a' => 1, 'b' => 2]];
$array[] = ['number' => 2, 'values' => ['a' => 4, 'b' => 1]];
$array[] = ['number' => 2, 'values' => ['a' => 1, 'b' => 4]]; // same "number" as the previous so get the sum between "a" of the previous and "a" of this, the same for "b"
$array[] = ['number' => 2, 'values' => ['a' => 1, 'b' => 1]]; // same "number" as the previous so get the sum between "a" of the previous and "a" of this, the same for "b"
$array[] = ['number' => 3, 'values' => ['a' => 2, 'b' => 4]];

So the output should be

$array[0] : ['number' => 1, 'values' => ['a' => 1, 'b' => 2]];
$array[1] : ['number' => 2, 'values' => ['a' => 6, 'b' => 6]]; //a = 4 + 1 + 1     //b = 1 + 4 + 1
$array[2] : ['number' => 3, 'values' => ['a' => 2, 'b' => 4]];

To tell the truth I have trouble doing it even with simple foreach.

My brain can only go so far and no further.

$array_output = [];
foreach ($array as $k => $v){
    foreach ($array as $kk => $vv){
        if ($v['number'] == $vv['number']) {
            // ????
        }
    }
}

Anyone help me?

---

Another question in the same question

How to do the same thing for

$array[] = ['number' => 1, 'a' => 1, 'b' => 2];
$array[] = ['number' => 2, 'a' => 4, 'b' => 1];
$array[] = ['number' => 2, 'a' => 1, 'b' => 4];
$array[] = ['number' => 2, 'a' => 1, 'b' => 1];
$array[] = ['number' => 3, 'a' => 2, 'b' => 4];

so how to get the sum for same variable number for a and b variables?

Answer 1

Using array functions. The idea is to build an array where the "number" is the key with array_reduce and then to remove these keys with array_values. This way you know easily if a number has been already encountered and if you have to sum or to define a new key. array_values is finally used to remove these keys.

$result = array_values(
    array_reduce(
        array: $array,
        
        callback: function ($carry, $item) {
            
            [$number, $values] = [$item['number'], $item['values']];
            
            if (array_key_exists(key: $number, array: $carry)) {
                foreach ($values as $key => $value) {
                    $carry[$number]['values'][$key] += $value;
                }
            }
            else {
                $carry[$number] = $item;
            }
            
            return $carry;
        },
        
        initial: []
    )
);

print_r($result);

demo

Note that this code is written for PHP >= 8.0. To make it compatible with older versions, remove the parameter labels in function calls (callback:, key:, array:, etc.).

Answer 2

$seen = [];
$i = 0;
foreach ($array as $data) {
    $number = $data['number'];
    $a = $data['values']['a'];
    $b = $data['values']['b'];

    if (isset($seen[$number])) {
        $output[$seen[$number]]['values']['a'] += $a;
        $output[$seen[$number]]['values']['b'] += $b;
    } else {
        $output[] = $data;
        $seen[$number] = $i;
        $i++;
    }
    //$i++;
}

checking result

print_r($output);

gives me this

Array ( [0] => Array ( [number] => 1 [values] => Array ( [a] => 1 [b] => 2 ) ) [1] => Array ( [number] => 2 [values] => Array ( [a] => 6 [b] => 6 ) ) [2] => Array ( [number] => 3 [values] => Array ( [a] => 2 [b] => 4 ) ) )

edit: went back and saw C.H's comment about a wrong increment placement, code now corrected.

Just to add, to answer the follow up question you can remove all mentions of ['values'] to use the same logic for the simpler second array example.

Answer 3

So that you don't need to keep track of the indexes of data pushed into the result array nor need to re-index the result, push reference variables into the result array to represent each group.

Assuming all rows will have the same columns in the values subarray, you can unconditionally sum in a nested loop whenever a group is encountered more than once. (Demo)

$result = [];
foreach ($array as $row) {
    if (!isset($ref[$row['number']])) {
        $ref[$row['number']] = $row;
        $result[] =& $ref[$row['number']];
    } else {
        foreach ($row['values'] as $k => $v) {
            $ref[$row['number']]['values'][$k] += $v;
        }
    }
}
var_export($result);

This advice resembles many of my earlier answers on the topic of grouping and summing array data. My posts tagged with arrays + grouping + sum

Answer 4

Since everyone is writing, look at this other way that's a possible solution for the second part of the question.

It does a little more math but it works great.

$array[] = ['number' => 1, 'a' => 1, 'b' => 2];
$array[] = ['number' => 2, 'a' => 4, 'b' => 1];
$array[] = ['number' => 2, 'a' => 1, 'b' => 4];
$array[] = ['number' => 2, 'a' => 1, 'b' => 1];
$array[] = ['number' => 3, 'a' => 2, 'b' => 4];

$seen = [];
$output = [];
foreach ($array as $e) {
    $number = $e['number'];
    if (isset($number)) {
        if (!in_array($number,$seen)) {
            $seen[] = $number;
            $output[$number]['number'] = $number;
            foreach($array as $ee) {
                if ($number == $ee['number']) {
                    if (isset($output[$number]['a'])) {
                        $output[$number]['a'] = $output[$number]['a'] + $ee['a'];
                    } else {
                        $output[$number]['a'] = $ee['a'];
                    }
                    if (isset($output[$number]['b'])) {
                        $output[$number]['b'] = $output[$number]['b'] + $ee['b'];
                    } else {
                        $output[$number]['b'] = $ee['b'];
                    }
                }
            }
        }
    }
}
//here the output key is on `$number`
$output = array_values($output);
//here the output key it's in numeric incremental order . (Nothing changes in this case)
print_r($output);

Does not include the case of many variables other than $a and $b, but only sums the specified ones and groups by $number

Here a DEMO. Look at it.

I hope this helps.

Small update - General Case

If you need to sum each key except number replace the inner foreach like this

            foreach($array as $ee) {
                if ($number == $ee['number']) {
                    foreach ($ee as $k => $v) {
                        if ($k != 'number'){
                            if (isset($output[$number][$k])) {
                                $output[$number][$k] = $output[$number][$k] + $ee[$k];
                            } else {
                                $output[$number][$k] = $ee[$k];
                            }
                        }
                    }
                }
            }

Complete other working DEMO