PHP adding arrays / summing arrays

A question from my mailbox, answered in relation to our hotel. "I have a number of arrays in PHP and I want to add the elements of the arrays together". "There doesn't appear to be an array_sum function".

So in other words, my correspondent may have room occupancy data such as:

$bed1 = array(2,2,2,0,2,0,0);

$bed2 = array(1,1,1,1,1,0,0);

$bed3 = array(1,1,1,0,0,2,2);

$bed4 = array(0,0,0,0,0,0,0);

$bed5 = array(1,1,1,1,1,2,2);

and want to produce a report showing the nightly occupancy - perhaps to know how many breakfasts to prepare. What about

for ($k=0; $k<7; $k++) {

        $occupancy[$k] = $bed1[$k]+$bed2[$k]+$bed3[$k]

                +$bed4[$k]+$bed5[$k];

}

That code is horrid - it works with our 5 room place, but when we grow to 50 rooms ....

A good solution is to keep the data in an array of arrays - the "1", "2", "3" and so on in the variable names really should itself be a variable / subscript so that the summing can be done with a loop of loops:

$full = array($bed1,$bed2,$bed3,$bed4,$bed5);

combines the bedrooms and the the code to sum looks like:

for ($k=0; $k<7; $k++) {

        $sm = 0;

        for ($j=0; $j<count($full); $j++) {

                $sm += $full[$j][$k];

                }

        $ot[$k] = $sm;

        }

Which is slightly longer for my 5 rooms, but much MUCH shorter once we expand!

(See full source code here and run it here)
(written 2007-03-23, updated 2009-05-04)

Associated topics are indexed under

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