How do I sort a hash by its values?

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

Replies are listed 'Best First'.
Re: How do I sort a hash by its values? by tye (Sage) on Jan 13, 2002 at 04:24 UTC
Don't make another structure. Just keep both the array and the hash handy. If you want all of the values (sorted), you simply do: `my @values= @hash[@array];` So, if you want the 3rd key and value, you use: `my $key= @array[2]; my $value= $hash{$key};` [download] instead of, using your data structure: `my $key= $array_of_hashes[2]{key}; my $value= $array_of_hashes[2]{value};` [download] or `my( $key, $value )= @{$array_of_hashes[2]}{qw( key value )};` The original array and hash also store the data using quite a bit less memory.	[reply] [d/l] [select]
Re: How do I sort a hash by its values? by particle (Vicar) on Jan 13, 2002 at 02:46 UTC
you can read about this in perlman:perlfaq4. additionally, you can search here for 'sort hash values' or something similar. a little legwork goes a long way. ~Particle	[reply]
Re: Answer: How do I sort a hash by its values? by George_Sherston (Vicar) on Jan 13, 2002 at 02:52 UTC
Yeah, actually I did do the leg work and I did find out a bit about it... but the first place I looked was Q&A and it wasn't there. And I thought this was a subject that comes up quite often and wd be worth representing here. Your unhelpful (but easy) answer "a little legwork goes a long way" is an answer to any categorised question, no? § George Sherston	[reply]
Re: How do I sort a hash by its values? by George_Sherston (Vicar) on Jan 13, 2002 at 03:03 UTC
Warning: I'm the person who asked the question! How I'd do it is `my %hash = ( foo => 2, bar => 1, baz => 3, bun => 2, ); my @array = sort {$hash{$a} <=> $hash{$b}} keys %hash;` [download] Of course, this array only has the hash keys in it, albeit correctly sorted. If you want a data structure with both keys and values from `%hash` then you have to choose a data structure that meets your needs. A straight hash is no good, because you have duplicate values, so you'll lose some key / value pairs when you reverse them. An array of hashes is one choice: `my @array_of_hashes; push @array_of_hashes, {key => $_, value => $hash{$_}} for @sorted;` [download] And to see what that looks like, `use Data::Dumper; print Dumper(\@array_of_hashes);` [download] Gets you `$VAR1 = [ { 'value' => 1, 'key' => 'bar' }, { 'value' => 2, 'key' => 'bun' }, { 'value' => 2, 'key' => 'foo' }, { 'value' => 3, 'key' => 'baz' } ];` [download] ... but I'm interested to see what other monks come up with: it was my slight unease with this solution that prompted me to post this question.	[reply] [d/l] [select]
Re: How do I sort a hash by its values? by George_Sherston (Vicar) on Jan 13, 2002 at 02:48 UTC
Warning: I'm the person who asked the question! How I'd do it is `my %hash = ( foo => 2, bar => 1, baz => 3, bun => 2, ); my @array = sort {$hash{$a} <=> $hash{$b}} keys %hash;` [download] Of course, this array only has the hash keys in it, albeit correctly sorted. If you want a data structure with both keys and values from `%hash` then you have to choose a data structure that meets your needs. A straight hash is no good, because you have duplicate values, so you'll lose some key / value pairs when you reverse them. An array of hashes is one choice: `my @array_of_hashes; push @array_of_hashes, "$hash{$_} => $_\n" for @array;` [download] And to see what that looks like, `use Data::Dumper; print Dumper(\@array_of_hashes);` [download] Gets you `$VAR1 = [ '1 => bar', '2 => bun', '2 => foo', '3 => baz' ];` [download] ... but I'm interested to see what other monks come up with: it was my slight unease with this solution that prompted me to post this question. Originally posted as a Categorized Answer.	[reply] [d/l] [select]


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