PHP calculate running sum from array based on date value

Question

I need to create a PHP function that will loop through a multi-dimensional array and return a value which represents the sum of a certain key, where the value of another key is <= the date value passed into the function. Here is a sample array of the data array:

Array
(
[Nov 18, 2011] => Array
    (
        [C] => 100
        [I] => 100
        [M] => 100
    )
[Nov 22, 2011] => Array
    (
        [C] => 200
        [I] => 200
    )
[Nov 29, 2011] => Array
    (
        [C] => 300
        [I] => -300
    )
)

There will never be more than these 3 categories [C], [I] and [M] and the values for each date should be considered a running sum.

So, how do I calculate the value of the [C] category as of the Nov 22, 2011 date? The correct value is of course 300. (Being 100 from Nov 18 + 200 from Nov 22)

What if I needed to calculate the value of [I] as of Nov 29, 2011? The correct answer in this example would be 0. (Being 100 + 200 - 300)

I'm open to ideas on how best to achieve this. My instinct is to have some kind of function and then pass in the category and date values. Thanks.

For clarity are you storing the sum or calculating the sum? You said the values for each should be the sum, but your example shows a recalculation. — Jason McCreary

TheOx TheOx · Accepted Answer · 2011-12-08T03:35:27

Depends on how many times you're likely to want to do this and if you'll need to do it for each category, etc whether or not you use a function or just a simple loop.

Either way you could put the following into a function and just pass in $target_date and the category (replacing the hard-coded "C" I'm using for this example):

$c_total = 0;
foreach($main_array as $date => $sub_array)
{
    if($date <= $target_date)
    {
        $c_total += $sub_array["C"];
    }
}

EDIT: For clarity here's the function using strtotime() to convert the date values to timestamps for easier comparison:

function getCategoryTotal($target_date, $category)
{
    $c_total = 0;
    $target_date = strtotime($target_date);
    foreach($main_array as $date => $sub_array)
    {
        if(strtotime($date) <= $target_date)
        {
            $c_total += $sub_array[$category];
        }
    }
    return $c_total;
}

PHP calculate running sum from array based on date value

1 Answers