From: Joel VanderWerf <vjoel@...>
Date: 2005-05-26T06:58:50+09:00
Subject: Re: Multilevel hash

aartist wrote:
> With perl it's easy to write:
> 
> $Q{$date}{$song_played} += 1
> 
> How I can accomplish the same thing with ruby?
> 
> Thanks!
> 
> http://pleac.sourceforge.net/pleac_ruby/index.html didn't help much
> here.
> 

irb(main):001:0> mh = Hash.new {|h,k| h[k] = {} }
=> {}
irb(main):002:0> mh[1][2] = 3
=> 3
irb(main):003:0> mh
=> {1=>{2=>3}}

You can also do variable-level hashing:

irb(main):006:0> pr = proc {|h,k| h[k] = Hash.new(&pr) }
=> #<Proc:0x4021eb08@(irb):6>
irb(main):007:0> vh = Hash.new(&pr)
=> {}
irb(main):008:0> vh[1][2][3][4] = 5
=> 5
irb(main):009:0> vh
=> {1=>{2=>{3=>{4=>5}}}}

(This is ruby-talk folklore!)