in reply to (Ovid) RE: RE: RE: From one beginner to others . . .
in thread From one beginner to others . . .

But your comparison isn't fair. You let the regex do way much work than needed. There's no need to parse the entire line, and only assign if there are exactly four fields - you aren't doing that for the split cases either. Also, you only have one set of parens, yet you do four assignments. Picking a simpler regex, and doing just one assignment improves the speed with 50%! 
$a=$1 if $myvar =~ /^[^,]+,([^,]+)/

[download]

Still not as fast as the split, but it shows that proper Benchmarking is an art.

-- Abigail

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(Ovid): The monk recants
by Ovid (Cardinal) on Jul 16, 2000 at 04:08 UTC
    D'oh! I optimized the split but not the regex :( That'll teach me to be careless. For honesty's sake: 

    timethese(1000000, { 
    Regex  => '$a=$1 if $myvar   =~ /^[^,]+,([^,]+)/',
    Split1 => '$result = (split /,/, $myvar)[1]',
    Split2 => '$result = (split /,/, $myvar, 4)[1]',
    Split3 => '$result = (split /,/, $myvar, 3)[1]'
});

Benchmark: timing 1000000 iterations of Regex, Split1, Split2, Split3.
+..
     Regex: 14 wallclock secs (14.12 usr +  0.00 sys = 14.12 CPU)
    Split1: 17 wallclock secs (16.54 usr +  0.00 sys = 16.54 CPU)
    Split2: 16 wallclock secs (16.75 usr +  0.00 sys = 16.75 CPU)
    Split3: 14 wallclock secs (13.02 usr +  0.00 sys = 13.02 CPU)

    [download]
    I'm going to cry myself to sleep tonight.

    Curiously, though, it was the null assignments that appeared to be killing the efficiency ($a=$1, $b=$2, $c=$3, $d=$4) much more than the unoptimized regex. Hmmm....

    Cheers,
    Ovid

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