Re: Multiple Sort on selected column

in reply to Multiple Sort on selected column

Why not Sort::Key? Is it just because it's on CPAN? (Yes, even you can use CPAN) If it's just for learning, that's one thing, but if that were the case, why use sort instead of rolling your own sorting routine? Ok, I have the answer for that: you don't want to learn the details of sorting, you just want to learn how to use sort. But to that I say that it's an arbitrary line, and, for productivity reasons, I'd suggest learning Sort::Key and Sort::Key::Multi/Sort::Key::Maker as your arbitrary line instead. So, instead of the idiomatic:

@ranked = sort { $a->{FIRST} cmp $b->{FIRST} or $a->{LAST} cmp $b->{LA
+ST} or $a->{AGE} <=> $b->{AGE} } @employees;
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(note that we're comparing ages with the <=> operator, not cmp, so that 9 and 19 will sort properly, using cmp will not cause these to sort properly) learning to use Sort::Key might be more useful. For example:

#!/usr/bin/perl

use strict;
use warnings;
use Sort::Key qw(multikeysorter);

my @employees = ( 
    { FIRST => 'Bill',   LAST => 'Gates',     
      SALARY => 600000, AGE => 45 },
    { FIRST => 'George', LAST => 'Tester',
      SALARY =>  55000, AGE => 29 },
    { FIRST => 'Sally',  LAST => 'Developer', 
      SALARY =>  55000, AGE => 29 },
    { FIRST => 'Joe',    LAST => 'Tester',    
      SALARY =>  55000, AGE => 29 },
    { FIRST => 'Steve',  LAST => 'Ballmer',   
      SALARY => 600000, AGE => 41 } 
);

my %types = (
             FIRST  => 'str',
             LAST   => 'str',
             SALARY => 'int',
             AGE    => 'int',
            );

my @sort = @ARGV; # not comma-separated, just for ease
@sort = map uc, @sort; # so I don't have to hold the shift key down.
my $sorter = multikeysorter( sub { my $A = $_; map { $A->{$_} } @sort 
+}, @types{@sort} );
my @ranked = $sorter->(@employees);

foreach my $emp (@ranked) {
    print "$emp->{SALARY}\t$emp->{AGE}\t$emp->{FIRST}\t$emp->{LAST}\n"
+;
}
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And then, as an example:

$ perl x.pl first age
600000  45      Bill    Gates
55000   29      George  Tester
55000   29      Joe     Tester
55000   29      Sally   Developer
600000  41      Steve   Ballmer
$ perl x.pl age first
55000   29      George  Tester
55000   29      Joe     Tester
55000   29      Sally   Developer
600000  41      Steve   Ballmer
600000  45      Bill    Gates
$ perl x.pl age last first
55000   29      Sally   Developer
55000   29      George  Tester
55000   29      Joe     Tester
600000  41      Steve   Ballmer
600000  45      Bill    Gates
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Simple, huh? :-)

Update: And for reversing, add the following line right after the my %types declaration:

@types{map -$_, keys %types} = map -$_, values %types;
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This will create the key -FIRST with value -str. And then the my $sorter line becomes:

my $sorter = multikeysorter( sub { my $A = $_; map { $A->{s/^-//r} } @
+sort }, @types{@sort} );
[download]

This removes the - sign when looking up the value in the employee hash, but keeps the - sign when passing in the types to sort. And now?

$ perl5.14.2 x.pl -age last first
600000  45      Bill    Gates
600000  41      Steve   Ballmer
55000   29      Sally   Developer
55000   29      George  Tester
55000   29      Joe     Tester
[download]

Note that the /r flag is new in 5.14.0, if you are running something older, you'll have to use:

my $sorter = multikeysorter( sub { my $A = $_; map { (my $k = $_) =~ s
+/^-//; $A->{$k} } @sort }, @types{@sort} );
[download]

Comment on Re: Multiple Sort on selected column Select or Download Code

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Re^2: Multiple Sort on selected column by huchister (Acolyte) on Oct 19, 2012 at 14:05 UTC
Wasn't exactly the answer I was looking for, but you shown me the alternative way to solve this which may come in handy in near future. thanks!	[reply]

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