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Re: map vs for\foreach.

by sn1987a (Deacon)
on Mar 11, 2015 at 14:33 UTC ( [id://1119641]=note: print w/replies, xml ) Need Help??


in reply to map vs for\foreach.

You are not comparing apples to apples. You map loop assigns (copies) the entire array in addition to incrementing each element. If you drop the assignment, map beats foreach.

My results

foreach(@a){$_+=1;};

real    0m4.941s
user    0m1.096s
sys    0m3.604s

[download]
----------------------- 
@a = map{$_+= 1} @a;

real    0m6.248s
user    0m2.652s
sys    0m2.900s

[download]
------------------------ 
map{$_+= 1} @a;

real    0m3.224s
user    0m2.908s
sys    0m0.232s

[download]

Note: It is generally considered poor form to use map only for its side effects.

Updated to clean up and add note

Update 2:

More rigorous timing show that foreach is indeed faster --> Re^3: map vs for\foreach.

Replies are listed 'Best First'.
Re^2: map vs for\foreach.
by builat (Monk) on Mar 11, 2015 at 14:38 UTC
    In my case:
    foreach(@a){$_+=1;};


real    0m3.756s
user    0m3.588s
sys    0m0.120s

    [download]
    map{$_+= 1} @a;

real    0m5.233s
user    0m5.056s
sys    0m0.164s

    [download]
[reply]
[d/l]
[select]

      My previous timings where just from a single run of each program. Using Benchmark and repeating to verify consistent results, I find that foreach is indeed faster.

      use strict;
use warnings;
use Benchmark;

my @a;
$a[$_] = int( rand(100) ) for ( 0 .. 10000000 );

cmpthese(
    -30,
    {
        'foreach'      => sub { foreach (@a) { $_ += 1; } },
        'map (assign)' => sub { @a = map { $_ += 1 } @a; },
        'map (bare)'   => sub { map { $_ += 1 } @a; },
    }
);

      [download]

      Results: 

                   s/iter map (assign)   map (bare)      foreach
map (assign)   2.06           --         -40%         -76%
map (bare)     1.23          67%           --         -59%
foreach       0.501         311%         146%           --

      [download]

[reply]
[d/l]
[select]

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