From: Daniel Sheppard <daniels@...>
Date: 2006-10-30T10:18:32+09:00
Subject: Re: How can i do 'foreach (reverse sort { $hasref->{$a} <=> $hasref->{$b} } keys %{$hasref})..' in ruby

> For the archive:
> 
> My working line is know:
> 
> clients.sort{|(k1,v1),(k2,v2)| v2 <=> v1}.each{|k,v| 
>       printf("% 7i %s\n",v, k)
> }

For the simple case (such as yours) where the values being sorted are
numeric, I find it neater to just do:

clients.sort_by{|k,v| -v}.each {|k,v|
	printf("% 7i %s\n",v, k)
}

Or in the general case:

clients.sort_by{|k,v| v}.reverse.each {|k,v|
	printf("% 7i %s\n",v, k)	
}

Or:

clients.sort_by{|k,v| v}.reverse_each {|k,v|
	printf("% 7i %s\n",v, k)	
}

Which is probably clearest in intention (looking at the original code
you post, it's not immediately apparent the it's a reverse sort). These
methods have the added benefit of also being the faster code (sort_by is
much faster than sort).

require 'benchmark'
hash = {}
1_000_000.times {|i| hash[i] = rand}
Benchmark.bm(22) {|bm|
  bm.report('sort') {hash.sort{|(k1,v1),(k2,v2)| v2 <=> v1}.each{|k,v|}}
  bm.report('sort_by @-') {hash.sort_by{|k,v| -v}.each {|k,v|}}
  bm.report('sort_by reverse') {hash.sort_by{|k,v| v}.reverse.each
{|k,v|}}
  bm.report('sort_by reverse_each') {hash.sort_by{|k,v| v}.reverse_each
{|k,v|}}
}

                            user     system      total        real
sort                   58.094000   0.719000  58.813000 ( 99.922000)
sort_by @-             10.297000   0.046000  10.343000 ( 14.750000)
sort_by reverse        10.922000   0.063000  10.985000 ( 14.687000)
sort_by reverse_each   10.000000   0.016000  10.016000 ( 12.094000)