Re: Transform hash key?

Uri Guttman <uri@xxxxxxxxxxxxxxx> wrote in
news:x7wtggtf56.fsf@xxxxxxxxxxxxxxxx:

>>>>>> "ASU" == A Sinan Unur <1usa@xxxxxxxxxxxxxxxxxxx> writes:
>
> ASU> my %h = map { $_ => 1 } ('aaa' .. 'zzz');
>
> ASU> cmpthese -1, {
> ASU> map => sub { %h = map { uc $_ => $h{$_} } keys %h },
> ASU> for => sub { $h{uc $_} = delete $h{$_} for keys %h; },
> ASU> };
>
> this benchmark has a common problem in that you don't set up the hash
> the same way for each run.

I actually thought about this before posting.

> the first time you call either sub, the hash will have only
> upper case keys. now i doubt that uc will be faster or slower
> given any mix of input case

Which is why I decided not worry about it (in this case).

> but it still is wrong.

I am not sure it is that wrong.

> if the transform were something whose speed was data dependent,
> this benchmark would be very bogus.

Absolutely.

> the map one could be fixed just by assigning it to a different hash.
> the for one would need a fresh hash each time as it modifies it in
> place. so you would need to do the same work for each one and my best
> idea would be to copy the %h to %h2 inside each sub and use that as
> the input (and you can use it for the output of the map. also choosing
> a different output hash for the map could affect speed as well.
>
> this is just a small lesson on the difficulty of properly benchmarking
> apples and apples.

Do you meam I should use:

#!/usr/bin/perl

use warnings;
use strict;

use Benchmark qw( cmpthese );

my %h = map { $_ => 1 } ('aaa' .. 'zzz');

cmpthese -1, {
map => sub { my %h2 = %h; %h2 = map { uc $_ => $h{$_} } keys %h },
for => sub { my %h2 = %h; $h2{uc $_} = delete $h2{$_} for keys %h2; },
};
__END__

D:\Home\asu1\UseNet\clpmisc> s.pl
Rate map for
map 7.31/s -- -39%
for 12.0/s 64% --

Or, should I omit the my %h2 = %h in the 'map' version?

D:\Home\asu1\UseNet\clpmisc> s.pl
Rate for map
for 12.1/s -- -3%
map 12.4/s 3% --

I don't think the latter version is fair to 'for' though.

Sinan

--
A. Sinan Unur <1usa@xxxxxxxxxxxxxxxxxxx>
(reverse each component and remove .invalid for email address)

comp.lang.perl.misc guidelines on the WWW:
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.

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