Re: sort and hash

Let's say you have a hash like so:

my %sequence = (
   1345 => 10,
   123  => 20,
   500  => 30,
);
[download]

You can add more key/value pairs like so:

$sequence{901} = 40;
[download]

Let's say that your id is stored in the variable $id and the score is stored in the variable $score. You can add this information to the hash like so:

$sequence{$id} = $score;
[download]

If you want to sort the data by say, the id, you can get a list of the keys with the keys built-in function and use the sort built-in function, specifying that you want to sort numerically with the "spaceship" operator <=> like so:

print "$_ => $sequence{$_}\n" for sort {$a<=>$b} keys %sequence;
[download]

Perl's motto is 'There Is More Than One Way To Do It'. Give us some more context, like what these id's and scores really look like and we can help even more.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

Comment on Re: sort and hash Select or Download Code

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Re: Re: sort and hash by kaweh (Initiate) on Sep 22, 2003 at 23:14 UTC
I need to create a hash first. At first I want to use push. Then I find in the book, it said don't use push or pop. Yeah, your suggestion is also a good way. Then I will sort by scores:) Thank you very much! kaweh	[reply]
3Re: sort and hash by jeffa (Bishop) on Sep 23, 2003 at 00:51 UTC
You are most welcome. :) And welcome to the Monastery. Limbic~Region metioned to me that you might be wanting to preserve the sort, that is, the keys stay sorted even after you add new ones. You can use the CPAN module Tie::Hash::Sorted for this, but first see A Guide to Installing Modules if you are not familiar with the CPAN. Tie's are, in my opinion, a bit hard to grasp if you are new to Perl (see perltie), but here goes anyway. :) `use strict; use warnings; use Data::Dumper; use Tie::Hash::Sorted; my %sequence = ( 1345 => 10, 123 => 20, 500 => 30, ); print Dumper \%sequence; # and here's the part that makes ears bleed ... tie my %sorted_sequence, 'Tie::Hash::Sorted', Hash => \%sequence, Sort_Routine => sub {[sort {$a <=> $b} keys %{$_[0]}]}, ; print Dumper \%sorted_sequence; $sorted_sequence{901} = 40; $sorted_sequence{201} = 50; print Dumper \%sorted_sequence;` [download] `Data::Dumper` is another CPAN module, but it comes with your Perl installation so you don't have to install it like you do `Tie::Hash::Sorted`. Once you have \ installed it, run the above example and notice the output. Note that even though your hash stays 'magically' sorted, there are a lot of CPU cycles burned to achieve it. In other words, if you really don't need to keep the hash sorted, then don't don't keep it sorted. Also, don't rule out using an array. Hashes are really good for quick lookups. If you are more concerned with sorting then looking up items, use an array. jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR B--B--B--B--B--B--B--B-- H---H---H---H---H---H--- (the triplet paradiddle with high-hat)	[reply] [d/l]