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Problem: Find the sum of the values in 'subtotal' for each 'id' and store the respective sum for each id in an array (or variables).

My sloppy solution at the moment is to run a foreach with multiple if statements inside that count the occurrences. This is adequate for something like 5 ids, but I have to iterate this over 38 ids. I would like to store the results sequentially in an array if possible.

How can I make it more efficient? Any and all help will be appreciated. (See my sloppy solution at the end of this for a good chuckle)

Desired Result:

  • sum of all ID 1 = 10
  • sum of all ID 2 = 18
  • sum of all ID 3 = 14
  • sum of all ID 4 = 4
  • sum of all ID 5 = 3

Array Code for Manipulation 

    $someArray = array(

    array(
        'id'=> 1,
        'subtotal'=> 5),
    array(
        'id'=> 1,
        'subtotal'=> 5),
    array(
         'id'=> 2,
         'subtotal'=> 6), 
    array(
         'id'=> 2,
         'subtotal'=> 6),
    array(
         'id'=> 2,
         'subtotal'=> 6),
    array(
         'id'=> 3,
         'subtotal'=> 7),
    array(
         'id'=> 3,
         'subtotal'=> 7),
    array(
         'id'=> 4,
         'subtotal'=> 2),
    array(
         'id'=> 4, 
         'subtotal'=> 2),
    array(
         'id'=> 5,
         'subtotal'=> 3),
    );

Sloppy Solution

$sum_id_1 = 0;
$sum_id_2 = 0;
$sum_id_3 = 0;
$sum_id_4 = 0;
$sum_id_5 = 0;

foreach ($someArray as $k) {

    if ($k['id'] == 1) {
        $sum_id_1 += $k['subtotal'];
    }

    if ($k['id'] == 2) {
        $sum_id_2 += $k['subtotal'];
    }

    if ($k['id'] == 3) {
        $sum_id_3 += $k['subtotal'];
    }

    if ($k['id'] == 4) {
        $sum_id_4 += $k['subtotal'];
    }

    if ($k['id'] == 5) {
        $sum_id_5 += $k['subtotal'];
    }
}

Sloppy Solution Output (on echo)

  • 10
  • 18
  • 14
  • 4
  • 3
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1 Answer

up vote 2 down vote accepted 
$sum = array_reduce($someArray, function($result, $item) {
    if (!isset($result[$item['id']])) $result[$item['id']] = 0;
    $result[$item['id']] += $item['subtotal'];
    return $result;
}, array());

var_dump($sum); // array(5) { [1]=> int(10) [2]=> int(18) [3]=> int(14) [4]=> int(4) [5]=> int(3) }

For PHP <= 5.3 perform the counting in loop manually:

$sum = array();

foreach ($someArray as $item) {
    if (!isset($sum[$item['id']])) $sum[$item['id']] = 0;
    $sum[$item['id']] += $item['subtotal'];
}
share|improve this answer
 
That was fast! Trying it out as we speak! Edit: Thank you zerkms, I've been wrangling with this for good four hours. Your solution would never have come across my mind. Also if you don't mind me asking, what are some good books to learn the logic necessary to solve problems like this in the future? –  PontusTrade Jul 24 '12 at 5:07
 
@PontusTrade: It would be nice if you upvote and check my answer then (there are arrows on the left and green checkmark sign) ;-) –  zerkms Jul 24 '12 at 5:11
 
@PontusTrade zerkms is just scary freaky that way. Makes me rather envious when I see something like this in under a few minutes. –  Fluffeh Jul 24 '12 at 5:13
 
@PontusTrade: I'm not sure about books. I've never read anything specific, it's just about decoupling a task to a smaller. In this case the obvious solution is: loop over each element and calculate subtotal somewhere. That's how you would do that if you do that manually - so you do the same in your code. –  zerkms Jul 24 '12 at 5:14
 
Upvoted! Thanks again. –  PontusTrade Jul 24 '12 at 5:15
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