From: Peter Szinek <peter@...>
Date: 2007-04-29T21:04:06+09:00
Subject: Partitioning with Set.divide

Hello all,

I have been playing with partitioning a set recently and I am stuck with 
an issue. The whole story is here:

http://www.rubyrailways.com/partitioning-sets-in-ruby/

A quick version for those who would not like to read the article:

Consider this input:

a 53 2 3
b 8 62 1 23
a 9 0 31
b 4 45 4 16 7
b 1 23
c 3 42 2 31 4 6
a 1 3 22
a 7 83 1 23 3
b 1 14 4 15 16 2
c 5 16 2 34

the goal is to create a partition based on the character in the first 
column, i.e.:

<Set: <Set: {"a 9 0 31", "a 7 83 1 23 3", "a 53 2 3", "a 1 3 22 "}>, 
<Set: {"b 1 23 ", "b 1 14 4 15 16 2", "b 8 62 1 23", "b 4 45 4 16 7"}>, 
<Set: {"c 5 16 2 34", "c 3 42 2 31 4 6"}>}>

Which is exactly what Set.divide does. However, there is one problem: I 
would like to know if there are duplicate lines. I.e. divide returns the
same result, no matter that the input is this:

c 5 16 2 34
c 5 16 2 34
c 5 16 2 34

or this:

c 5 16 2 34

What I would need is a modified divide which returns also the count of 
the elements in the input set (at least for those elements which are 
more than once in the set). Is this doable or do I have to roll some 
code to do this for me additionally?

Cheers,
Peter

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