Group values and sum keys in flat, associative array

Question

Please help needed to solve output as array key sum and value by group.

My actual output :

$array = array(
    '7'=>'15',
    '20'=>'6',
    '11'=>'9',
    '14'=>'6',
    '4'=>'15'
 );

I need final array to sum of keys and group by value like :

$array = array('15' => 11, '6' => 34, '9' => 11);

Answer 1

Iterate the array and use each value as the keys in the result array. Use a null coalescing expression to fallback to zero when a specific value from the input array is encountered for the first time. As you iterate, simply add the input array's key to the result array's value "sum".

Code: (Demo)

$array = [
    '7' => '15',
    '20' => '6',
    '11' => '9',
    '14' => '6',
    '4' => '15'
 ];
 
 $result = [];
 foreach ($array as $key => $value) {
     $result[$value] = ($result[$value] ?? 0) + $key;
 }
 var_export($result);

Output:

array (
  15 => 11,
  6 => 34,
  9 => 11,
)