Indeed. There are trade-offs everywhere: by default, I always write 

 sort {} grep {} @foo;

[download]

so that the grep happens first. The speed is more important than the memory for almost everything I do.

Here's a little bit of lies/damn-lies/statistics demonstrating the speed difference on an array in which most values appear twice. 

#!/usr/local/bin/perl -w

use Benchmark;
use strict;

my @data;
my %seen;
foreach ( 1..100_000 ) { push @data, int($_/2) }
fisher_yates_shuffle ( \@data );

#my @gs = gs(); print join ( "\n", @gs );
#my @sg = sg(); print join ( "\n", @sg );

timethese ( 20, { sort_grep => \&sg,
                  grep_sort => \&gs,
} );

sub gs {
  return sort { $a <=> $b }
    grep { ! $seen{$_} ++ }@data;
}

sub sg {
  return grep { ! $seen{$_} ++ }
    sort { $a <=> $b } @data;
}

# fisher_yates_shuffle( \@array ) : from Perl Cookbook
sub fisher_yates_shuffle {
    my $array = shift;
    my $i;
    for ($i = @$array; --$i; ) {
        my $j = int rand ($i+1);
        next if $i == $j;
        @$array[$i,$j] = @$array[$j,$i];
    }
}

[download]

And the output I get: 

Benchmark: timing 20 iterations of grep_sort, sort_grep...
 grep_sort:  5 wallclock secs ( 4.70 usr +  0.02 sys =  4.72 CPU) @  4
+.24/s (n=20)
 sort_grep: 16 wallclock secs (15.56 usr +  0.03 sys = 15.59 CPU) @  1
+.28/s (n=20)

[download]

As a side note, I regard this kind of optimization as "habitual", rather than of the premature kind. <laugh>

In reply to Re: (tye)Re: Can Schwartzian transform be modified to sort an arrayref uniquely? by khkramer
in thread Can Schwartzian transform be modified to sort an arrayref uniquely? by corporate_gadfly

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.