user defined sorting functions, how to properly use them?

Question

I have always used this method for accomplishing this kind of sort, but doesn't look correct to me

usort($array, function($team1, $team2){

    $t1 = ($team1->points * 1000) + ($team1->goalsFor - $team1->goalsAgainst);
    $t2 = ($team2->points * 1000) + ($team2->goalsFor - $team2->goalsAgainst);

    if($t1 == $t2) return 0;
    return $t1 > $t2 ? 1 : -1;
});

an alternative to this method is to use str_pad, which does nearly the same

basically what I do is to separate with zeros the sorting subjects

$t1 = 32008; // 32 points with a GD of 8
$t2 = 32003; // 32 points with a GD of 3

but what if a team got a weird goals difference?

$t1 = 32008; // 32 points with a GD of 8
$t2 = 33000; // 32 points with a GD of 1000

clearly this can't happen, but it's an example

is this a good way? how about the 32-64 bit / floating numbers [im]precision limits?

does someone have suggestions for this?

thank you :)

feel free to improve the title

C. K. Young · Accepted Answer · 2013-09-01 14:49:02Z

1

A better approach is this:

function ($team1, $team2) {
    if ($team1->points != $team2->points) {
        return $team1->points > $team2->points ? 1 : -1;
    }
    $diff1 = $team1->goalsFor - $team1->goalsAgainst;
    $diff2 = $team2->goalsFor - $team2->goalsAgainst;
    if ($diff1 != $diff2) {
        return $diff1 > $diff2 ? 1 : -1;
    }
    return 0;
}

Or, in Java (using Guava), I'd write it like this:

public int compare(Team team1, Team team2) {
    return ComparisonChain.start()
            .compare(team1.getPoints(), team2.getPoints)
            .compare(team1.getGoalsFor() - team1.getGoalsAgainst(),
                     team2.getGoalsFor() - team2.getGoalsAgainst())
            .result();
}

Clearly, PHP doesn't have ComparisonChain, but it shouldn't be hard to implement.

answered Sep 1, 2013 at 14:49

C. K. Young

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1 Comment

user652649 Over a year ago

hmmm i clearly have picked a too simple example, but i can't actually imagine nothing better at the moment, but i remember that i had difficulties in sorting with specific rules, like "relevance multipliers" or equivalent-level sorting subjects. anyway, this answers the question. thanks

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