Re: sort with special order

On Fri, Jul 24, 2009 at 11:01, Jo for lists and
groups<ourlists@xxxxxxxxxx> wrote:
> How about this? Jo
>
>
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my @list = qw/dog is a there/;
> my @sortOrder = (3,1,2,0);
> my @sorted;
> foreach (@sortOrder) { push(@sorted,$list[$_]); }
>
> print "@sorted";
> exit;
snip

What do you do when the list is qw/there a dog is/?  Your code does
not sort the data.  I guess you could go insane and write something
like:

my %position = (
    there => 0,
    is    => 1,
    a     => 2,
    dog   => 3,
);

for my $word (@list) {
    $sorted[$position{$word}] = $word;
}

But that would only work if the list will only contain one item each
of "there", "is", "a", or "dog".  The sort is not only more flexible,
it is faster (due to the low number of items to be sorted and the fact
that sort is implemented in C):

positional_hash => there is a dog
sort => there is a dog
positional_array => there is a dog
                     Rate  positional_hash positional_array             sort
positional_hash  253734/s               --             -11%             -15%
positional_array 284350/s              12%               --              -5%
sort             297890/s              17%               5%               --

#!/usr/bin/perl

use strict;
use warnings;

use List::Util qw/maxstr/;
use Benchmark;

my %position = (
        there => 0,
        is    => 1,
        a     => 2,
        dog   => 3,
);

my @sortOrder = (3,1,2,0);

my @a = qw/dog is a there/;

my %subs = (
        sort   => sub {
                return join " ", sort { $position{$a} <=> $position{$b} } @a;
        },
        positional_array => sub {
                my @sorted;
                push @sorted, $a[$_] for @sortOrder;
                return join " ", @sorted;
        },
        positional_hash => sub {
                my @sorted;
                $sorted[$position{$_}] = $_ for @a;
                return join " ", @sorted;
        },
);

for my $sub (keys %subs) {
        print "$sub => ", $subs{$sub}->(), "\n";
}

Benchmark::cmpthese -1, \%subs;


-- 
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.

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