PHP Sum keys in multidimensional array that match another key

Question

I have a multidimensional array and I need to add up some of the data.

My array looks like this (there is a lot more data I cropped out for the example):

Array
(
    [0] => Array
        (
            [date] => 20-02-2014
            [tool] => mystuff1
            [usage] => 447
            [minutes] => 6705
        )

    [1] => Array
        (
            [date] => 20-02-2014
            [tool] => mystuff2
            [usage] => 20
            [minutes] => 1200
        )

There will be more than one sub-array that has tool=mystuff1 and I want to add the "minutes" key up for all the ones that have mystuff1. Ultimately I want to do the same with mystuff2 added up (there are other 'tool' keys besides those that will be done as well.)

Ive tried several examples I found on this site but they all seem sum based on the 1 key name i.e. 'minutes' but not anything I can find where I can sum the 'minutes' when 'tool' also matches.

scrowler · Accepted Answer · 2014-02-21 02:31:49Z

1

You can loop through your array and add the minutes value to the array key of an output array:

$output = array();

foreach($your_array as $current) {
    // create the array key if it doesn't exist already
    if(!array_key_exists($current['tool'], $output))
        $output[$current['tool']] = 0;

    // add minutes to the current tool total
    $output[$current['tool']] += $current['minutes'];
}

This way you can expect a result like this:

Array
(
    [mystuff1] => 6705
    [mystuff2] => 1200
)

answered Feb 21, 2014 at 2:31

scrowler

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5 Comments

Jason Over a year ago

That works great. One thing though, if I had a similar setup but wanted to subtract the values from eachother wouldnt I use a -= instead of the +=? If I do that now I get a negative number instead of the proper results. ex: with += I get 13410 with -= I get -13410

scrowler Over a year ago

What do you mean by proper results? If I removed a number from zero I'd expect it to be negative...

Jason Over a year ago

well lets say one of them has value of 6500 and the other has a value of 500. If I += them it is now 7000. For some reason if I -= it shows -7000. I would expect 6000 since 6500-500=6000. Do I misunderstand what that code is actually doing?

scrowler Over a year ago

No - your first example is adding both values together, the second is subtracting both values (the loop will perform the same operator every time) - how do you differentiate between which values need to be added or subtracted, and is having -500 as one of your values not acceptable? (6500 + -500 = 6000)

Jason Over a year ago

Ok, gotcha. Thanks for the code. It works great for the first question.

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