How to sum the 2nd level values of a 2-dim array based on the 2nd level keys?

Question

I have a multi-dimensional array like this:

array(
      0 => array(
         11 => 18.000,
         14 => 25.100,
         15 => 5.000,
         16 => 8.000,
         19 => 21.600'
     ),
     1 => array(
         11 => 9.100,
         12 => 2.700,
         14 => 2.300,
         15 => 18.800,
         16 => 9.500,
         17 => 6.900,
         19 => 9.400'
    ),
    2 => array(
        14 => 5.700
    ),
    3 => array(
       17 => 2.800,
       20 => 6.000
   ),
   4 => array(
       24 => 5.000,
       25 => 6.000,
       26 => 2.7
   ),
   5 => array(
       16 => 2.200
   ),
   6 => array(
      14 => 13.000,
      15 => 2.000,
      16 => 4.300,
      19 => 6.000
  ),
  7 => array(
      32 => 5.000,
      36 => 18.500
  )
 )

The second-level arrays have varying length. But I want to get the values of the elements with similar keys and add them together to get a grand total.

For example, if the array is called $multi_dime. I would want to get $multi_dime[0][11] add it to $multi_dime[1][11] and so on.

If the key does not exist in a following array. It should just add 0 or ignore it. The code should proceed to do this for all keys in the second-level array and store the results in another array like:

array(  11 => 27.1,  14 => 46.1, ...)

How can I achieve this? The array will always be two dimensional, but can be of any length and the second level arrays can also be any length.

score 1 · Accepted Answer · answered Apr 28 '15 at 12:25

Just use a foreach or for loop. That is how you work with arrays, be it one, two, three, four, or two-hundred dimensional. Since you will have more than one sum, make the sums variable an array. Declare it outside your loop because you will need it when the loop is complete.

$sums = array();
foreach($multi_dime as $vals)
{
    foreach($vals as $key=>$val)
    {
        // Now we are looping through all values in the second dimension.
        // If the key is not in the sums array, make it.
        if(!isset($sums[$key])) $sums[$key]=0;
        // We add this sum to the key now.
        $sums[$key]+= $val;
    }
}
ksort($sums); // Just in case you want the keys in order.
print_r($sums); // See all the sums.

score 0 · Answer 2 · answered Jan 05 '18 at 12:50

Here is a less efficient (I assume) method for calculating the sum of all key-specific columns. The only difference is that there are no iterated conditionals in my method, it does call "heavier" functions though.

Code: (Demo)

$result=[];
foreach($array as $subarray){
    $subarray=array_diff_key($subarray,$result);  // deny iteration of previously summed subarray keys
    foreach($subarray as $k=>$v){
        $result[$k]=array_sum(array_column($array,$k));  // sum the whole array's column
    }
}
var_export($result);

If this was my project, I'd be writing my code very similarly to kainaw's (but not exactly). I don't prefer declaring the initial value as 0 then adding to 0 in the same iteration -- it's unnecessary double-handling.

Code: (Demo)

foreach($array as $subarray){
    foreach($subarray as $k=>$v){
        if(!isset($result[$k])){
            $result[$k]=$v;
        }else{
            $result[$k]+=$v;
        }
    }
}
var_export($result);

How to sum the 2nd level values of a 2-dim array based on the 2nd level keys?

2 Answers2