assigning 'points' to array based on position, how to deal with ties?

Question

I have an array filled with arrays with a name, then a gross amount. This array is then being assigned a "points total" based on their gross ranking. The points decreases by 2 with every rank, but my issue is how can i deal with ties? Ideally i'd see how many ties, add up the total points for those rankings, then divide it by how many are tied, but i have no clue how to really accomplish that

Here is my array usort:

function grossSort($gross, $compare) {
    if($gross['gross'] > $compare['gross'])
        return -1; // move up
    else if($gross['gross'] < $compare['gross'])
        return 1; // move down
    else
        return 0; // do nothing
}

turns my array into this:

Array
(
    [0] => Array
        (
            [instr] => lee
            [gross] => 2094
        )

    [1] => Array
        (
            [instr] => steve
            [gross] => 1334
        )

    [2] => Array
        (
            [instr] => nick
            [gross] => 0
        )

    [3] => Array
        (
            [instr] => amber
            [gross] => 0
        )

    [4] => Array
        (
            [instr] => lindsey
            [gross] => 0
        )

)

And here's what im doing to assign points now:

$maxpoints = 40;            
for($i = 0; $i < count($trainergross); $i++){
    $trainergross[$i]['points'] += $maxpoints;
    $maxpoints -=2;
}

and now my array looks like this:

Array
(
    [0] => Array
        (
            [instr] => lee
            [gross] => 2094
            [points] => 40
        )

    [1] => Array
        (
            [instr] => steve
            [gross] => 1334
            [points] => 38
        )

    [2] => Array
        (
            [instr] => nick
            [gross] => 0
            [points] => 36
        )

    [3] => Array
        (
            [instr] => amber
            [gross] => 0
            [points] => 34
        )

    [4] => Array
        (
            [instr] => lindsey
            [gross] => 0
            [points] => 32
        )

)

And here's my issue, there are 4 people "tied" but getting decreasing points, I have no clue how to address this in the current way my code is set up. Anyone have any guidance?

Answer 1

You can store the last known value as you iterate, and only decrease the points when the value changed. The array is sorted, so the equal elements will be adjacent.

/**
 * award average of points to a number of elements.
 * @param arrayref $trainergross - reference to the original array
 * @param int $award - total points to award
 * @param int $start_index - which element to start with?
 * @param int $count - how many elements should be awarded points?
 * @return void
 */
function award_points(&$trainergross, $award, $start_index, $count=1)
{
    if(!$count || $award<1) return; // if noone is waiting for the award, OR there is no award, bail out

    // $awards holds total award, and we need to
    $avgPoints = $award / $count;

    // award points to $count previous elements
    for($j = $start_index; $j < $start_index + $count; ++$j)
    {
        // in case points key was not initialized, php will issue a notice.
        if(!isset($trainergross[$j]['points'])) $trainergross[$j]['points'] = 0;

        $trainergross[$j]['points'] += $avgPoints;
    }
}

/**
 * This is increased on purpose
 * the first check will be <some number> vs null, which will result in -=2.
 * this is to eliminate additional !== null test inside the loop.
 */
$maxpoints = 42;

// This will be used to store number of consecutive elements
$count = 0;

// This will be used to store total points to award
$award = 0;

// Here we will store last gross value
$last = null;

for($i = 0; $i < count($trainergross); $i++)
{
    $maxpoints -= 2;

    // if gross has not changed, just count consecutive elements and continue
    if($last == $trainergross[$i]['gross'])
    {
        $award += $maxpoints;
        $count++;
        continue;
    }

    // store gross value
    $last = $trainergross[$i]['gross'];

    // now really distribute the points we've gathered in award by now
    award_points($trainergross, $award, $i - $count, $count);

    // reset count back to 1 (there is only 1 "consecutive" element now)
    $count = 1;

    // next element will get this award
    $award = $maxpoints;
}

// now we have to award points again
// the loop ended, but $count of elements are still awaiting points...
award_points($trainergross, $award, $i - $count, $count);