sort hash by value

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

What is the best way to sort the hash by value and printing out the top 5 results? For array, I guess you can do something like

@count_s = sort {
     $reportn{$a} <=> $reportn{$b};
} @count_s;

foreach (@count_s[0..4]) {
    print "$_ ====> $reportn{$_}\n";
}
[download]

But not sure about hash as below method does not work.
is it just my grammar mistake?

foreach my $hero ( sort keys %total_o) {
   if  ($reportn_o{$hero}) {
         @reportnL = sort { $total_o{$a} <=> $total_o{$b} } values (%t
+otal_o{$hero});
   }
}

for (@reportnL[0..4]) {
  print "$_\n";
}
[download]

Comment on sort hash by value Select or Download Code

Replies are listed 'Best First'.
Re: sort hash by value by salva (Canon) on Dec 02, 2007 at 19:55 UTC
Sorting the full list of items to get just the top n is not the most efficient way, there are better algorithms. See Selection_algorithm. You can also use Sort::Key::Top instead of implementing those algorithms yourself ;-)	[reply]
Re: sort hash by value by moritz (Cardinal) on Dec 02, 2007 at 18:01 UTC
Since you can't reverse a hash in the general case, you can just make a list of lists: `my @list = map { [$_, $hash{$_}] } keys %hash; # sort it: @list = sort { $a->[1] cmp $b->[1] }; # now you can print it` [download]	[reply] [d/l]
Re: sort hash by value by grep (Monsignor) on Dec 02, 2007 at 18:11 UTC
I'm not quite sure what your doing with all that code, there seem to be quite a few mistakes. Which makes it hard for me to follow. But as to your main point of the sort not working: You're sending in the values but treating them like keys and trying to do a lookup. `@reportnL = sort { $total_o{$a} <=> $total_o{$b} } values (%total_o{$hero});` Change it to `@reportnL = sort { $total_o{$a} <=> $total_o{$b} } keys %total_o ;` UPDATE: Just noticed his was my 500th post. grep `One dead unjugged rabbit fish later...`	[reply] [d/l] [select]
Re: sort hash by value by johngg (Canon) on Dec 02, 2007 at 18:44 UTC
`for (@reportnL[0..4]) { print "$_\n"; }` [download] Your use of an array slice here seems a little unusual, not incorrect but not the way I suspect most would approach the task. I would perhaps do `for ( 0 .. 4 ) { print qq{$reportnL[$_]\n}; }` [download] or, more probably `print qq{$reportnL[$_]\n} for 0 .. 4;` [download] I hope this is of interest. Cheers, JohnGG	[reply] [d/l] [select]