Most efficient way to mathematically add two multidimensional arrays? - php

Question

Consider two simple arrays:
<?php
$array1 = array(
'blue' => 5,
'green' => array(
'square' => 10,
'sphere' => 0.5,
'triangle' => 3
),
'red' => array(
'circle' => 1000,
),
'black' => 4,
);
$array2 = array(
'blue' => 1,
'green' => array(
'square' => 11,
'circle' => 5,
),
'purple' => 10,
'yellow' => array(
'triangle' => 4
),
'black' => array(
'circle' => 6,
),
);
I need to mathmatically add together in a recursive way, each value from each $array1 and $array2.
Preserve keys
Where a key does not exist in $array1 but does exist in $array2, the final array would simply contain the value of $array2 (and the other way around as well)
Where they exist in both, the numeric values would be added +
Non-numeric values wouldn't be touched
If a value on $array1 points to another sub-array, and in $array2 it points to a value, the end value would result in that key containing a subarray that contains the values from $array1 plus a new key/value using the parent name and it's value (see black in the example)
Should be able to work at virtually unlimited nesting
To clarify, e.g. if we said
<?php
$final = array_merge_special($array1, $array2);
// We would end up with, if you var_export()'d final, something like:
// (Note: Hope I didn't make mistakes in this or it will be confusing,
// so expect mild human error)
$final = array(
'blue' => 6, // 5+1
'green' => array(
'square' => 21, // (10+11)
'sphere' => 0.5, // only in $array1
'triangle' => 3 // only in $array1
'circle' => 5, // only in $array2
),
'purple' => 10, // only in $array2
'yellow' => array( // only in $array2
'triangle' => 4
),
'red' => array( // only in $array1
'circle' => 1000,
),
'black' => array(
'circle' => 6, // untouched, while $black is present in both, the $array1 value does not have a 'circle' key, and is actually only a key/value (see below)
'black' => 4, // the key/value from $array1 that was not a subarray, even though it was a subarray in $array2
),
);
This seems outragously daunting to me. I know I could loop over one array and get easily recursively add the values, and I have this working (somewhat), but it's when I get into special rules (such as ones for black) that I can't even imagine how broken code would look. There has to be a way to do this would looping over each array individually and unset()'ing values to merge?

Answer 1

You would use array_walk_recursive (see: See php Manual here) and possibly array_merge_recursive. I'd have to think it through further to get the full picture.
OK, decided that this wouldn't work! Array_walk_recursive doesn't pass keys that hold arrays to the function. This problem kept flowing aroung in my brain, so I just had to write a function to do it! Here it is:
function dosum($arin) {
$arout = array();
foreach ($arin as $key1 => $item1) {
$total = 0;
if(is_array($item1)) {
foreach($item1 as $key2 => $item2) {
if(is_numeric($key2))
$total += $item2;
else
if(is_array($item2))
$arout[$key1] = dosum(array($key2 => $item2));
else
$arout[$key1][$key2] =$item2;
}
if($total)
if(isset($arout[$key1]))
$arout[$key1][$key1] = $total;
else
$arout[$key1] = $total;
}
else
$arout[$key1] = $item1;
}
return $arout;
}
For the 2 arrays given, you would use it like this:
print_r(dosum(array_merge_recursive($array1, $array2)));