From: Christoph Rippel <crippel@...>
Date: 2001-03-07T01:18:00+09:00
Subject: [ruby-talk:12153] Re: (long) Re: hash.invert loses data if  equal values exist - is this the right behaviour?

> From: Tammo Freese [mailto:tammo.freese@offis.de]
[...]
> Or is the morale that I should not invert hashes with equal values
> because the results are too difficult to predict?

FYI - hash.invert is a ``left inverse'' under
composition regardless of the ambiquites of it's
actually value ...


class Hash
def * (other)
        res = clone
        each do |l,r|
                raise 'composition undefined' unless other.key? r
                res[l] = other[r]
        end
        res
end
end


hsh = Hash[1, 3, 2, 3,4,4,"a",4 ]
ish = hsh.clone.invert

p ish*hsh  # {4=>4, 3=>3} 

Christoph