PHP: Group (multidimensional, associative) array and sum values by specific key

Question

I've searched a lot of examples with group/sum array values - unfortunately I can't resolve my problem. I got array $data which looks like this:

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2014
            [context] => 'aaa'
        )

    [1] => Array
        (
            [0] => 12
            [1] => 2014
            [context] => 'aaa'
        )       

    [2] => Array
        (
            [0] => 5
            [1] => 2014
            [context] => 'zzz'
        )               
)

I would like to group and sum its values (but not all) by 'context'.

So desired output is:

Array
(
    [0] => Array
        (
            [0] => 13
            [1] => 2014
            [context] => 'aaa'
        )

    [1] => Array
        (
            [0] => 5
            [1] => 2014
            [context] => 'zzz'
        )       

)

I'm far from this expected output. I've tried something like:

$result = array();
foreach ($data as $subArray) 
{
  foreach ($subArray as $row)
  {
    $result[$row['context']] = $row['context'];
    $result[$row['1']] = $row['1'];
    $result[$row['0']] += $row['0'];
  }
}

But of course it doesn't work and I'm out of ideas. Can you please give me a hint? What else can I try?

prodigitalson · Accepted Answer · 2014-12-12 16:34:57Z

1

The problem is you were overwriting elements in your loop and you were counting on an extra nesting level:

$data = array(
    0 => array(
            0 => 1,
            1 => 2014,
            'context' => 'aaa'
        ),

    1 => array(
            0 => 12,
            1 => 2014,
            'context' => 'aaa'
        ),       

    2 => array(
            0 => 5,
            1 => 2014,
            'context' => 'zzz'
        )               
);

$result = array();

// the elements to sum - since everything is mixed together.
// the values in this array should be the index you want to sum
// ex. $sum = array(2,3) would sum $data[2] and $data[3]
$sum = array(0);

foreach ($data as $subArray) 
{
  $context = $subArray['context'];

  if (!isset($result[$context])) {
    // initialize the result for this context because it doesnt exist yet
    $result[$context] = array();
  }

  // you had an extra nesting level here
  // $row was equiv to 'aaa' or '2014' whereas you thought it was
  // array('context' => 'aaa', 0 => 5, 1 => '2014')
  foreach ($subArray as $idx => $val)
  {
    // you were also constantly overrwriting $result'aaa'] (or whatever context) here
    if (in_array($idx, $sum)) {
       $result[$context][$idx] = isset($result[$context][$idx])
         ? $result[$context][$idx] + $val
         : $val;
    } else {
      // this will keep overwriting anything that isnt in the $sum array
      // but thats ok because those values should be the same with, or the last
      // one should win. If you need different logic than that then adjsut as necessary
      $result[$context][$idx] = $val;
    }
  }
}

printf('<pre>%s</pre>', print_r($result, true));

edited Dec 12, 2014 at 16:34

answered Dec 11, 2014 at 18:20

prodigitalson

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4 Comments

suz Over a year ago

It works great except for one issue: if I would like to sum more then 1 element, for instance: $sum = array(0 => 2, 1 => 3); //etc always element for index 0 is also summed up. I know that question was little bit different, but is it possible to sum other element than this with index 0? Is it a good solution: if ($idx === 0) {$result[$context][$idx] = $val;} ?

prodigitalson Over a year ago

Yeah actually thats my fault at one point i was using array_intersect_key so the keys in $sum were the indexes in $subArray you wanted to sum. But then i switched to in_array... should be corrected now.

suz Over a year ago

it's not :) Still value with index 0 is summed.

prodigitalson Over a year ago

@suz: I just tested it again locally and it seems to be working for me just fine. Can you post a new question with your updated code, or a link to a phpfiddle or something?

MH2K9 · Accepted Answer · 2014-12-11 16:27:38Z

1

You can done it using an temporary array(here $newArr). Can try something like this

$newArr = array();
foreach($your_arr as $key=>$val){
    $index = $val['context'].$val[1];
    if(isset($newArr[$index])){
        $val_0 = $newArr[$val['context'].$val[1]][0] + $val[0];
        $newArr[$val['context'].$val[1]] = array($val_0, $val[1], 'context'=>$val['context']);
    }else{
        $newArr[$val['context'].$val[1]] = $val;
    }
}
$result = array_values($newArr);
print '<pre>';
print_r($result);
print '</pre>';

edited Dec 11, 2014 at 16:27

answered Dec 11, 2014 at 16:14

MH2K9

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Comments

mickmackusa · Accepted Answer · 2023-05-15 21:20:06Z

0

Use a single loop and add a reference on the first element of the first encountered row with a given context value. If a context value is encountered more than once, add its first element's value to the reference and unset the entire row.

Code: (Demo)

foreach ($array as $i => &$row) {
    if (!isset($ref[$row['context']])) {
        $ref[$row['context']] = &$row[0];  // create reference
    } else {
        $ref[$row['context']] += $row[0];  // sum new value and reference value
        unset($array[$i]);                 // remove the unneeded row
    }
}
var_export($array);

answered May 15, 2023 at 21:20

mickmackusa♦

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