in reply to map vs for\foreach.

Picking your syntax based on benchmarks of trivial operations is total folly.

Use map if you want to get back a list. Don't otherwise.

Now, there can be non-trivial performance implications in similar syntax choices between for() and while() when reading from a (large) file, for example. But you also likely would not discover those from running benchmarks of trivial operations.

The benchmark results presented so far mostly illustrate differences in the trivial operations being done, not any performance difference that is likely to actually matter if you were changing useful code between map/for() [for cases of code where for() made sense].

- tye        

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Re^2: map vs for\foreach. (bench)
by tye (Sage) on Mar 12, 2015 at 05:40 UTC

    Here's some trivial benchmarks that at least compare comparable operations and ones that are just slightly more than trivial: 

    #!/usr/bin/perl -w
use strict;
use Benchmark 'cmpthese';
my @a = 1..1000;
sub p {
    my( $a ) = @_;
    if( $a & 1 ) {
        return $a*$a;
    } else {
        return ($a-1)*($a+1);
    }
}
cmpthese( -2, {
    for  => sub { my $t = 0; for( @a ) { $t += p($_) } return $t },
    map  => sub { my $t = 0; map $t += p($_), @a; return $t },
} );
cmpthese( -2, {
    map  => sub { my @b = map p($_), @a; return $b[-1] },
    for  => sub { my @b; for( @a ) { push @b, p($_) } return $b[-1] },
} );

    [download]

    And here are my results: 

          Rate for map
for 2101/s  -- -1%
map 2127/s  1%  --

      Rate map for
map 1981/s  -- -0%
for 1987/s  0%  --

    [download]

    So I don't even have to give my explanation of why Benchmark.pm saying "20% faster" almost never has any practical meaning.

    - tye        

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