Merge and sum multiple multidimensional associative arrays

Question

I'm needing a way to merge several arrays ( probably around 8 ) and sum any duplicate keys or sub-keys.

For example:

$arr1 = [
    "Friday" => ["Breakfast" => 32, "Lunch" => 45],
    "Sunday" => ["Lunch" => 12]
];

$arr2 = [
    "Sunday" => ["Breakfast" => 7, "Lunch" => 3],
    "Monday" => ["Breakfast" => 12]
];

$arr3 = [
    "Monday" => ["Breakfast" => 31]
];

And the output should be something like this:

array (
  'Friday' => 
  array (
    'Breakfast' => 32,
    'Lunch' => 45,
  ),
  'Sunday' => 
  array (
    'Lunch' => 15,
    'Breakfast' => 7,
  ),
  'Monday' => 
  array (
    'Breakfast' => 43,
  ),
);

How could I combine this? I've tried using array_map().

But that seemed to fail with multidimensional arrays like this. Also tried using foreach(), but that got pretty convoluted.

Here's my attempt:

$total = array_map( function( $arr1, $arr2, $arr3 ){
    return( $arr1 + $arr2 + $arr3 );
}, $arr1, $arr2, $arr3 );

score 2 · Accepted Answer · answered Dec 22 '14 at 18:52

Try this solution. You can add any count of arrays. But keep names as $arr1-$maxArraysCount

$arr1 = array(
    "Friday" => array(
        "Breakfast" => 32,
        "Lunch" => 45
    ),
    "Sunday" => array(
        "Lunch" => 12
    )
);

$arr2 = array(
    "Sunday" => array(
        "Breakfast" => 7,
        "Lunch" => 3
    ),
    "Monday" => array(
        "Breakfast" => 12
    )
);

$arr3 = array(
    "Monday" => array(
        "Breakfast" => 31
    )
);


$maxArraysCount = 8;
$return = array();
for($i = 1; $i < $maxArraysCount; $i++){
    $arr = 'arr' . $i;
    if(isset($$arr) && is_array($$arr)){
        foreach ($$arr as $day => $value) {
            foreach ($value as $eat => $count) {
                if(!isset($return[$day][$eat])) $return[$day][$eat] = 0;
                $return[$day][$eat] = $count + $return[$day][$eat];
            }
        }
    }
}

echo "<pre>";print_r($return);

Here is output:

Array
(
    [Friday] => Array
        (
            [Breakfast] => 32
            [Lunch] => 45
        )

    [Sunday] => Array
        (
            [Lunch] => 15
            [Breakfast] => 7
        )

    [Monday] => Array
        (
            [Breakfast] => 43
        )

)

Really appreciated this answer, @Oleg. I have a follow-up question here that you may have some insight on? http://stackoverflow.com/questions/27650302/merge-and-sum-multiple-multidimensional-arrays-in-php — Adam, Dec 25 '14 at 19:59

mickmackusa · Answer 2 · 2020-12-15T04:02:24.300

Because your data structure is fully associative, array_merge_recursive() will keep your data integrity intact. Once the arrays are merged, you only need to iterate the days' meals, cast the single values as array type (turning them into single-element arrays if not already arrays), then unconditionally all array_sum().

Code: (Demo)

$arr1 = [
    "Friday" => ["Breakfast" => 32, "Lunch" => 45],
    "Sunday" => ["Lunch" => 12]
];

$arr2 = [
    "Sunday" => ["Breakfast" => 7, "Lunch" => 3],
    "Monday" => ["Breakfast" => 12]
];

$arr3 = [
    "Monday" => ["Breakfast" => 31]
];

$result = [];
foreach (array_merge_recursive($arr1, $arr2, $arr3) as $day => $meals) {
    foreach ($meals as $meal => $counts) {
        $result[$day][$meal] = array_sum((array)$counts);
    }
}    
var_export($result);

Output:

array (
  'Friday' => 
  array (
    'Breakfast' => 32,
    'Lunch' => 45,
  ),
  'Sunday' => 
  array (
    'Lunch' => 15,
    'Breakfast' => 7,
  ),
  'Monday' => 
  array (
    'Breakfast' => 43,
  ),
)

To avoid variable-variables in Oleg's answer, you can stuff each of your input arrays into an array, then merge them (to preserve the duplicated day names).

Code: (Demo)

$result = [];
foreach (array_merge([$arr1], [$arr2], [$arr3]) as $array) {
    foreach ($array as $day => $meals) {
        foreach ($meals as $meal => $count) {
            $result[$day][$meal] = ($result[$day][$meal] ?? 0) + $count;
        }
    }
}

or more efficiently, prepopulate the result array with your first array.

$result = $arr1;
foreach (array_merge([$arr2], [$arr3]) as $array) {
    foreach ($array as $day => $meals) {
        foreach ($meals as $meal => $count) {
            $result[$day][$meal] = ($result[$day][$meal] ?? 0) + $count;
        }
    }
}

Merge and sum multiple multidimensional associative arrays

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