Reverse sort array

rethaew has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Reverse sort array by ikegami (Patriarch) on Aug 19, 2009 at 22:22 UTC
sort allows for a custom compare function. `my $sorter = ( $reverse ? sub { $b cmp $a } : sub { $a cmp $b } ); for (sort $sorter @array) { ... }` [download]	[reply] [d/l]
Re^2: Reverse sort array by rethaew (Sexton) on Aug 19, 2009 at 22:30 UTC
Thank you for your reply. I am sorry but it is not immediately clear to me how to use this code you have written.	[reply]
Re^3: Reverse sort array by AnomalousMonk (Archbishop) on Aug 19, 2009 at 22:41 UTC
`my $reverse = its_reverse_sorting(time); # set or clear flag my $sorter = ( $reverse ? sub { $b cmp $a } : sub { $a cmp $b } ); for (sort $sorter @array) { ... }` [download]	[reply] [d/l]
Re^3: Reverse sort array by ikegami (Patriarch) on Aug 20, 2009 at 02:50 UTC
I renamed `$something` to `$reverse`, but it's otherwise a drop-in replacement for the code you posted.	[reply] [d/l] [select]
Re^2: Reverse sort array by rovf (Priest) on Aug 20, 2009 at 08:51 UTC
Or, if you want to do it without `?:` and add a slight touch of obfuscation: `for (sort { "-"x!!$reverse.1*($a cmp $b) } @array) { ... }` [download] -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l] [select]
Re^3: Reverse sort array by ikegami (Patriarch) on Aug 20, 2009 at 14:40 UTC
If I wanted to avoid the conditional operator, it would be because I had many options. In that case, I would use a lookup table. `my $sorter = $lkup{$method}{$direction}; for (sort $sorter @array) { ... }` [download]	[reply] [d/l]
Re: Reverse sort array by Tanktalus (Canon) on Aug 19, 2009 at 22:29 UTC
Why not just do the reverse when requested? `my @ordered = sort @array; @ordered = reverse @array if $something;` [download] You could use eval STRING, but that's evil, so let's avoid that. Another possibility is: `foreach ($something ? reverse sort @array : sort @array)` [download] but I don't really like that - too much copying (especially if you have a sort function). Another one that is close to being nice is: `use Sort::Key qw(keysort rkeysort); my $sorter = $something ? \&rkeysort : \&keysort; foreach ($sorter->(sub { $_ }, @array) )` [download] (Untested - you may need to pass in \@array.) Along these lines, you could use the multikeysorter from Sort::Key) to create a sorter sub that sorts in the correct order - you pass in something based on the $something.	[reply] [d/l] [select]
Re^2: Reverse sort array by rethaew (Sexton) on Aug 19, 2009 at 22:36 UTC
thank you `foreach ($something ? reverse sort @array : sort @array)` [download] worked well for me.	[reply] [d/l]
Re: Reverse sort array by AnomalousMonk (Archbishop) on Aug 19, 2009 at 22:34 UTC
A similar approach, but likely slower due to more levels of indirection: `>perl -wMstrict -le "sub ascending { $a cmp $b } sub descending { - ascending() } my @ra = qw(q w e r t y u i o p); my $sorter = 'descending'; @ra = sort $sorter @ra; print qq{@ra}; $sorter = 'ascending'; @ra = sort $sorter @ra; print qq{@ra}; " y w u t r q p o i e e i o p q r t u w y` [download]	[reply] [d/l]
Re^2: Reverse sort array by johngg (Canon) on Aug 20, 2009 at 13:24 UTC
You can get by with just one sorting routine by reversing the arguments as needed. `$ perl -Mstrict -wle ' > my @arr = qw{ q w e r t y u i o p }; > my $sc = sub { my( $a, $b ) = @_; $a cmp $b }; > my $rev = 0; > my @asc = sort { $rev ? $sc->( $b, $a ) : $sc->( $a, $b) } @arr; > $rev = 1; > my @des = sort { $rev ? $sc->( $b, $a ) : $sc->( $a, $b) } @arr; > print qq{@arr\n@asc\n@des};' q w e r t y u i o p e i o p q r t u w y y w u t r q p o i e $` [download] I hope this is of interest. Cheers, JohnGG	[reply] [d/l]