Sum array values depending dates non-singularity

Question

Let's say I have 2 same sized arrays filled with values. The dates array contains dates in string format and the costs array contains numeric costs. For instance:

$dates = array('2001-01-01', '2001-02-01', '2001-02-01', '2001-02-01', '2001-03-01', '2001-04-01', '2001-04-01', '2001-05-01');
$costs = array(5, 10, 20, 4, 30, 14, 2, 0);

What I want is to sum the numbers from the costs array into a new array only when the dates in the $dates array are repeated. When this happens, the new array value must be a sum of its "left siblings".The rest new array value(s) should be 0. In other case (when the date is unique in the array, then the new array value is 0).

This should be the result of the above proccess:

$newarr = array(5, 0, 0, 34, 30, 0, 16, 0);

jcsanyi · Accepted Answer · 2013-06-02 21:16:54Z

3

How about this?

$result = $costs;
foreach ($dates as $i => $d) {
    if ($i > 0 && $dates[$i - 1] == $dates[$i]) {
        $result[$i] += $result[$i - 1];
        $result[$i - 1] = 0;
    }
}
print_r($result);

We're starting with our $costs array, and looping through all the dates... every time we detect that the date is the same as the previous entry, we zero out the previous entry and add it's value to our current location.

Alternate Solution

This isn't exactly what you asked for, but I suspect a more useful solution might be this:

$result = array();
foreach ($dates as $i => $d) {
    $result[$d] = (isset($result[$d]) ? $result[$d] : 0) + $costs[$i];
}
print_r($result);

This will produce a result of:

array(
    '2001-01-01' => 5,
    '2001-02-01' => 34,
    '2001-03-01' => 30,
    '2001-04-01' => 16,
    '2001-05-01' => 0
)

edited Jun 2, 2013 at 21:16

answered Jun 2, 2013 at 20:58

jcsanyi

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1 Comment

Ricardus Over a year ago

Man...that was fast! You also nailed it after posting the alternate solution, which is even better than what I had in mind! Thank you!

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