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Re: Date to be sorted in descending and time in ascending

by Cristoforo (Deacon)
on May 18, 2012 at 23:27 UTC ( #971373=note: print w/ replies, xml ) Need Help??


in reply to Date to be sorted in descending and time in ascending

Using unpack in a Schwartzian Transform.

#!/usr/bin/perl use strict; use warnings; use 5.014; print map {$_->[0]} sort {$b->[1] cmp $a->[1] || $a->[2] cmp $b->[2]} map {[ $_, unpack "a8a6", $_ ]} <DATA>; __DATA__ 20010405000000 20050405005000 20020405081200 20080405022500 20080405022600 20080405023500 20090405022500 20090405022300 20090405022900 20090405022100


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Re^2: Date to be sorted in descending and time in ascending
by aaron_baugher (Deacon) on May 19, 2012 at 19:32 UTC

    I wondered if someone would suggest unpack. I don't use it often enough to remember the format codes without checking the man page, but it seems like it's often the fastest solution for this kind of thing. So I added yours to my benchmark, and found that unpack was slightly slower than substr/substr in this case. (I'd guess that if it were necessary to break the string into three or more pieces, unpack would come out ahead.) Both were still slower than the non-Schwartzian substr/substr sort, as detailed in my other post, though. Results and code:

    bannor:~/work/perl/monks$ perl 971240.pl 1000000 s/iter stunpack stsubst plainsort stunpack 12.4 -- -10% -31% stsubst 11.2 11% -- -24% plainsort 8.54 46% 31% -- bannor:~/work/perl/monks$ cat 971240.pl #!/usr/bin/env perl use Modern::Perl; use Benchmark qw(:all); my @data; push @data, int(rand(1000000000000))+10000000000000 for (1..$ARGV[0]); cmpthese( 10, { 'stunpack' => \&stunpack, 'stsubst' => \&stsubst, 'plainsort' => \&plainsort, }); sub plainsort { my @d = sort { substr($b,0,8) <=> substr($a,0,8) or substr($a,8) <=> substr($b,8) } @data; } sub stsubst { my @d = map { $_->[0] } sort { $b->[1] <=> $a->[1] or $a->[2] <=> $b->[2] } map { [ $_, substr( $_, 0, 8 ), substr( $_, 8)] } @data; } sub stunpack { my @d = map { $_->[0] } sort { $b->[1] <=> $a->[1] or $a->[2] <=> $b->[2] } map { [ $_, unpack "a8a6" ] } @data; }

    Aaron B.
    Available for small or large Perl jobs; see my home node.

      You should add salva's offering to your benchmark.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.

      The start of some sanity?

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