PHP: Avg Grade by category - php

Question

I'm fairly new to PHP and trying to sort a class project. I've banged away and can't see to sort it out, this is the last remaining piece.
I have a form - submit essentially 2 arrays I'm trying to determine the average score for based upon the category groupings. 1. ($_post['category']), ($_post['score']) - with category being a text based array and score obviously being numbers based.
How would I go about finding the average score for each category? I've tried various options to for mapping the two arrays and then trying to average the grades. I can get the total score average pretty easily, but finding a ways to do this by each category individually is tripping me up.
I need to apply a weight to each category score, but that seems pretty easy once you get the above sorted.
Thanks,
Steve
$_POST example:
Array (
[0] => Assignment
[1] => Assignment
[2] => Assignment
[3] => Assignment
[4] => Assignment
[5] => Assignment
[6] => Exam
[7] => Assignment
[8] => Assignment
[9] => Assignment
[10] => Exam
[11] => Exam
[12] => Final Project
)
Array (
[0] => 100
[1] => 100
[2] => 100
[3] => 98
[4] => 90
[5] => 92
[6] => 100
[7] => 100
[8] => 100
[9] => 100
[10] => 100
[11] => 92
[12] => 100
)

Answer 1

There are several ways to go about this, here's one:
// create arrays
$cat = array(
"Assignment", "Assignment", "Assignment",
"Assignment", "Assignment", "Assignment",
"Exam", "Assignment", "Assignment",
"Assignment", "Exam", "Exam", "Final Project");
$grade = array(100,100,100,98,90,92,100,100,100,100,100,92,100);
// create $result: key = cat, values = sum, count, avg = 0
$result = array_fill_keys($cat, array('sum' => 0, 'count' => 0, 'avg' => 0));
$max = count($cat);
// add grades to category in $result[cat][sum]
for ($i = 0; $i < $max; $i++)
$result[$cat[$i]]['sum'] += $grade[$i];
// count number of categories in $cat
$num = array_count_values($cat);
// fill $result[cat][count]...
// then divide each cat's sum by each cat's count => $result[cat][avg]
foreach ($result as $k => $v) {
$result[$k]['count'] = $num[$k];
$result[$k]['avg'] = round($result[$k]['sum'] / $num[$k], 2);
}
Result:
Array
(
[Assignment] => Array
(
[sum] => 880
[count] => 9
[avg] => 97.78
)
[Exam] => Array
(
[sum] => 292
[count] => 3
[avg] => 97.33
)
[Final Project] => Array
(
[sum] => 100
[count] => 1
[avg] => 100
)
)
see it working: http://codepad.viper-7.com/QQAaXD