How to grade scores in php - php

Question

I'm trying to grade some scores according to highest average obtained..
Here's my scripts
$scores_AND_ID = 'M2377O=100,M2727B=100,M5821K=100,M7492F=97.75,M7973O=96,M3487I=94,M7969O=93.13,M1452V=92.5,M4653O=92.38,M4158J=92.25,M2881A=89.38,M6112S=28.63,';
$out_score = chop($scores_AND_ID, ',');
$rr2 = explode(",", $out_score);
$array_un = array_unique($rr2);
foreach ($array_un as $key => $value) {
if ($value == "") {
continue;
}
$postion = positionNumbers($key);//1st,2nd,3rd function
$sec = explode("=", $value);
rsort($sec);
$stdntID = $sec[0]; //Student number
$stdntAV = $sec[1]; //Student Average
mysql_query("UPDATE score_table SET grade='$postion' WHERE avg='$stdntAV' ");
}
I'm using foreach key to assign grade position but isn't working properly.
Here's my result
Here's what I need to achieve.
1. 100---1st
2. 100---1st
3. 100---1st
4. 98---4th
5. 89.5--5th
6. 89---6th
7. 89---6th
8. 80---8th
Thanks Guys

Answer 1

I think the code you want is this:
<?php
$scores_AND_ID = 'M7492F=97.75,M7973O=96,M3487I=94,M2377O=100,M2727B=100,M5821K=100,M7969O=93.13,M1452V=92.5,M4653O=92.38,M4158J=92.25,M2881A=89.38,M6112S=28.63,';
// Gets all of the entries from the source string
$scores_array = array_unique(array_filter(explode(',', $scores_AND_ID)));
// Sets up an associative array of values (student id => score)
$score_map = [];
foreach ($scores_array as $record) {
[ $student_id, $score ] = explode('=', $record);
$score_map[$student_id] = $score;
}
// Ensure values are sorted numerically descending
uasort($score_map, function ($a, $b) {
if ($a > $b) {
return -1;
}
if ($a == $b) {
return 0;
}
return 1;
});
// Gets the maximum value from the scores
$previous_score = max(array_values($score_map));
$rank = 1;
$incrementer = 0;
foreach ($score_map as $student => $score) {
// If the score hasn't changed from it's previous value
// we increment a counter instead of the rank
if ($score == $previous_score) {
$incrementer++;
// Once it's changed, we update the rank based on the incrementer
// and then reset the incrementer
} else {
$rank += $incrementer;
$incrementer = 1;
}
$previous_score = $score;
// Updating database is left as an exercise to the reader
}

Answer 2

You should not update your records if grade is already set. If you print your query instead of executing it you will see that you set grade 1st, then you overwrite it with 2nd and then with 3rd.