From: Christoph Rippel <crippel@...>
Date: 2001-03-16T15:17:33+09:00
Subject: [ruby-talk:12715] Re: (long) Re: hash.invert loses data if equal values exist - is this the right behaviour?

> From: Charles Hixson [mailto:charleshixsn@earthhlink.net]
[...]
> >      Returns a new hash created by using hsh's values as keys, and the
> >      keys as values.  Note that the result is uncertain if equvalent
> >      hsh's values are associated to different keys.
> >
> >         h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
> >         h.invert   #=> {200=>"d", 300=>"y", 0=>"a", 100=>"n"}
> >
> > Thanks,
> >
> > -- Gotoken
> 
> What you want to return is a bag, not a set.  So the general inverse of a 
> hash would have the second element be a list of values:
>          h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "e"=>200, "a" 
> => 0, "k"=>100}
>          h.invert   #=> {200=>["d", "e"], 300=>["y"], 0=>["a"], 100=>["n", 
> "k"]}
Just,

out of curiosity is this the way CS-types use the term bag - or this all
applied to the full-fledged thing - i.e. a general relation?

Christoph