From: Brian Candler <b.candler@...>
Date: 2010-08-10T21:48:22+09:00
Subject: Re: hash

Dmitriy Makarov wrote:
>> do you need a multivalue hash?
>> {key => val1, val2, val3 ...}
> 
> Yes

(1)

myhash = Hash.new { |h,k| h[k] = [] }
myhash['key'] << 'val1'
myhash['key'] << 'val2'
myhash['key'] << 'val3'
p myhash
# {"key"=>["val1", "val2", "val3"]}
p myhash['key']
# ["val1", "val2", "val3"]

(2)

myhash = Hash.new { |h,k| h[k] = {} }
myhash['key']['val1'] = true
myhash['key']['val2'] = true
myhash['key']['val3'] = true
p myhash
# {"key"=>{"val3"=>true, "val1"=>true, "val2"=>true}}
p myhash['key'].keys
# ["val3", "val1", "val2"]

The latter has the property that duplicate values are eliminated, and 
it's very quick to test for a particular value:

if myhash['key']['val1']
  ... etc
end

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