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Re^2: sorting entires by date

by Aristotle (Chancellor)
on Jan 02, 2004 at 00:27 UTC ( #318201=note: print w/ replies, xml ) Need Help??

in reply to Re: sorting entires by date
in thread sorting entires by date

He has filenames in there, so assuming that the format is fixed is more than likely moot. But seeing as it is the last field we're interested, the following will work:

my @sorted = sort { substr( $a, 1 + rindex, $a, ':' ) cmp substr( $b, 1 + rindex, $b, +':' ) } <>;

Makeshifts last the longest.

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Re: Re^2: sorting entires by date
by jweed (Chaplain) on Jan 02, 2004 at 01:16 UTC
    The problem with this being that you have to substr twice for every comparison, which, when the file becomes large, is substatially more time consuming than the ST or GRT which does a substr for each line only. He explains that in this Unix Review Column.

    Who is Kayser Söze?
    Code is (almost) always untested.

      In a simplistic benchmark of a thousand records the straight substr $a cmp substr $b comes out over 180% quicker than the ST version. Using a GRT saves another 14%.

      The cost of the split in the ST outweights the repeated substr in this case.

      #! perl -slw use strict; use Benchmark qw[ cmpthese ]; open IN, '<', 'test.dat' or die $!; our @lines = <IN>; close IN; print "Sorting ", scalar @lines, $/; cmpthese( -3, { ST => q[ my @sorted = map $_->[0], sort{ $a->[4] <=> $b->[4] } map [ $_, split /:/ ], @lines; ], XX => q[ my @sorted = sort{ substr( $a, 19 ) cmp substr( $b, 19 ) } @lines; ], GRT=> q[ my @sorted = map{ substr $_, 10 } sort map{ substr( $_, 20 ) . $_ } @lines; ], }); __END__ P:\test>318176 Sorting 1000 Rate ST XX GRT ST 6.70/s -- -65% -69% XX 19.1/s 186% -- -13% GRT 21.9/s 227% 14% --

      Examine what is said, not who speaks.
      "Efficiency is intelligent laziness." -David Dunham
      "Think for yourself!" - Abigail

Re: Re^2: sorting entires by date
by ysth (Canon) on Jan 02, 2004 at 01:19 UTC
    If you have dates before and after time 1000000000 (Sept 2001), you need to use <=> instead of cmp (assuming traditional Unix epoch).

    Being able to do a numeric comparison on two substrings is one of those things that makes Perl Perl.

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