Sum the values of two associative multi-dimensional arrays in PHP

I am trying to sum the values of two associative arrays. This is the first array:

Array
(
[Jan 01, 2013] => Array
    (
        [COM] => 100
        [RES] => 200
    )

[Oct 28, 2014] => Array
    (
        [COM] => 300
        [RES] => 400
    )
)

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and this is the second array:

Array
(
[Jan 01, 2013] => Array
    (
        [COM] => 10
        [RES] => 20
    )

[Oct 28, 2014] => Array
    (
        [COM] => 30
        [RES] => 40
    )
)

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I need to sum the values from these two arrays so that it produces this result:

    Array
(
[Jan 01, 2013] => Array
    (
        [COM] => 110
        [RES] => 220
    )

[Oct 28, 2014] => Array
    (
        [COM] => 330
        [RES] => 440
    )
)

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I found this tutorial to sum values of associative arrays, but it does not seem to work with my multi-dimensional arrays. Any suggestions how to accomplish this? Thank you.
DanielAttardAsked:
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arnoldCommented:
You can use foreach $element in (@array) {
Then use the dereferencing to cycle through the second level in a similar way
$array[$elelemnt]
You would need to use exists test to avoid error of trying to add null values.

Are you using the storable module to store this data in a file that you then load/writeout?
0
ozoCommented:
change $sum = $in[$key] + $out[$key]; in the tutorial to
  if( is_array($in[$key]) ){
        $sum = array_mesh($in[$key], $out[$key]);
  }else{
        $sum = $in[$key] + $out[$key];
  }
0

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DanielAttardAuthor Commented:
Great stuff @ozo, this worked like a charm.  More importantly, I learned a few things in the process.  Thanks.
0
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