list-parsing problem

Hi People,

I have a silly little list-parsing problem that I can't get my head
around, and I'm sure some of you have come across it before.

I have a list like this:

1	a
2	b
2	c
3	a
4	d
4	d
4	e
4	f
5	g

and I want to make the first column non-redundant and collect the second
column values on the same line, like this:

1	a
2	b,c
3	a
4	d,e,f
5	g

Please note that line 4 only has one 'd'.

I've tried with both hashes and arrays (don't want to confuse you so I
won't display them here), but nothing really works...

I would really appreciate any help!

Marcus