How to merge two arrays by summing the merged values [duplicate]

Question

Possible Duplicate:
PHP: How to sum values of the array of the same key

I am looking for an array_merge() function that does NOT replace values, but ADDS them.

Example, this is the code I am trying:

    echo "<pre>";       $a1 = array(          "a" => 2         ,"b" => 0         ,"c" => 5     );      $a2 = array(          "a" => 3         ,"b" => 9         ,"c" => 7         ,"d" => 10     );      $a3 = array_merge($a1, $a2);     print_r($a3);  

Sadly, this outputs this:

Array (     [a] => 3     [b] => 9     [c] => 7     [d] => 10 ) 

I then tried, instead of array_merge, just simply adding the two arrays

$a3 = $a1 + $a2; 

But this outputs

Array (     [a] => 2     [b] => 0     [c] => 5     [d] => 10 ) 

What I truly want is to be able to pass as many arrays as needed, and then get their sum. So in my example, I want the output to be:

Array (     [a] => 5     [b] => 9     [c] => 12     [d] => 10 ) 

Of course I can schlepp and build some function with many foreach etc, but am looking or a smarter, cleaner solution. Thanks for any pointers!

Answer 1

$sums = array(); foreach (array_keys($a1 + $a2) as $key) {     $sums[$key] = (isset($a1[$key]) ? $a1[$key] : 0) + (isset($a2[$key]) ? $a2[$key] : 0); } 

You could shorten this to the following using the error suppression operator, but it should be considered ugly:

$sums = array(); foreach (array_keys($a1 + $a2) as $key) {     $sums[$key] = @($a1[$key] + $a2[$key]); } 

Alternatively, some mapping:

$keys = array_fill_keys(array_keys($a1 + $a2), 0); $sums = array_map(function ($a1, $a2) { return $a1 + $a2; }, array_merge($keys, $a1), array_merge($keys, $a2)); 

Or sort of a combination of both solutions:

$sums = array_fill_keys(array_keys($a1 + $a2), 0); array_walk($sums, function (&$value, $key, $arrs) { $value = @($arrs[0][$key] + $arrs[1][$key]); }, array($a1, $a2)); 

I think these are concise enough to adapt one of them on the spot whenever needed, but to put it in terms of a function that accepts an unlimited number of arrays and sums them:

function array_sum_identical_keys() {     $arrays = func_get_args();     $keys = array_keys(array_reduce($arrays, function ($keys, $arr) { return $keys + $arr; }, array()));     $sums = array();      foreach ($keys as $key) {         $sums[$key] = array_reduce($arrays, function ($sum, $arr) use ($key) { return $sum + @$arr[$key]; });     }     return $sums; } 

Answer 2

My contribution:

function array_merge_numeric_values() {     $arrays = func_get_args();     $merged = array();     foreach ($arrays as $array)     {         foreach ($array as $key => $value)         {             if ( ! is_numeric($value))             {                 continue;             }             if ( ! isset($merged[$key]))             {                 $merged[$key] = $value;             }             else             {                 $merged[$key] += $value;             }         }     }     return $merged; } 

Pass as many arrays to it as you want. Feel free to add some more defense, ability to accept multidimensional arrays, or type checking.

Demo: http://codepad.org/JG6zwAap