Looping over with arrays by grouping matching values

I am writing a module for my website, that gives a breakdown of test results, I need to get someout put similar to this,

Test Title

Average Mark 85%

Test Title 2

Average Mark 12%

The array I am getting 开发者_如何学编程from my database looks like this,

    Array
(
    [0] => Array
        (
            [result_id] => 11
            [test_taken] => 2011-10-04 16:22:59
            [mark] => 5
            [retaken] => false
            [tests_test_id] => 4
            [test_title] => Website Development CSS Basics
            [test_slug] => website-development-css-basics
            [mark_needed] => 90
            [retake] => Yes
            [topic_id] => 402
            [topics_topic_id] => 402
        )

    [1] => Array
        (
            [result_id] => 12
            [test_taken] => 2011-10-04 16:30:02
            [mark] => 50
            [retaken] => false
            [tests_test_id] => 5
            [test_title] => Another Test
            [test_slug] => another-test
            [mark_needed] => 10
            [retake] => No
            [topic_id] => 402
            [topics_topic_id] => 402
        )

)

This my query currently,

$this->db->select('results.result_id, results.test_taken, results.mark, results.retaken, results.tests_test_id, tests.test_title, tests.test_slug, tests.mark_needed, tests.retake, topics.topic_id, tests.topics_topic_id')
    ->from('results')
    ->join('tests', 'tests.test_id = results.tests_test_id', 'left')
    ->join('topics', 'topics.topic_id = tests.topics_topic_id', 'left');

    $query = $this->db->get();
    return $query->result_array();

I need to somehow group all the results the have same test id so that I can then get the mean average of the results using the mark key.

Is this possible in PHP?

---

This is the kind of thing you should get the database to do for you. Something along the lines of:

SELECT AVG(mark) FROM test_results GROUP BY tests_test_id

---

Create a new array and then loop though - adding as you go ?

$sumArray = array();

foreach ($myArray as $key=>$val) {
    $sumArray[$key]+=$val;
}

print_r($sumArray['test_id']);