In your initial question you stated, "The function itself is quite simple - it gets 3 scalars (one of which is a field of some object), checks a couple of if's on the values and some basic math (including modulo %), and returns an array with a couple of hashes, each with two numerical fields. That's it." But then the code you presented here shows a quagmire of complexity of loops within loops, greps within loops (which is another form of loop), sorting within loops (which implies more loops), and so on. Having first read your initial question (with no code posted), and then later reading the code you posted, I couldn't believe my eyes. My first thought was, "This must be a practical joke. We're being suckered." What you're calling "checking a couple of ifs and some basic math" is actually nested loops with sorting and greping inside of them. It couldn't get much worse from an efficiency standpoint than that.

Let's imagine a really simple case in this code fragment:

my $n = 100;
my $c = 0;
foreach (0 .. $n) {
    $c++;
}
print "$c\n";

[download]

That loop executes in O(n) time. Now consider this loop:

my $n = 100;
my $c = 0;
foreach my $outter (0 .. $n) {
    foreach my $inner (0 .. $n) {
        $c++;
    }
}
print "$c\n";

[download]

That chunk of code executes in O(n^2) time. That means that for 'n' there are n^2 iterations. If your code stopped there, you would still be questioning why it's taking so long. But it doesn't. I didn't wander through every level of looping, but I think your efficiency is going quadratic, which is to say, inefficient. I don't know how you could equate multiple layers of nested loops with "The function itself is quite simple..." These are mutually exclusive conditions.

It could be there is a more efficient algorithm out there to solve the problem you're tackling. OR, it could be that you have one of those problems for which there is no efficient solution. If that's the case, thank goodness you've got a computer to do it for you. ;)


Dave

In reply to Re^3: Some code optimization by davido
in thread Some code optimization by roibrodo

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