[Tutor] Help with lists

[Mike Yuen]

I've got a bit of a problem with lists that I need some help with.

What I have is a pair of sub-elements (20 and A4) within each element such
as: 
[20, A4] <-- We'll call this pair "big element"

There are over 20000 such big elements.  Not all of them are going to have
a unique 1st sub-element (ie: the above big element has 20 as it's 1st
sub element)

What i'm trying to do is group them all the big elements with
the same 1st subelements together.
For example:
[20, A4]
[20, A2]
[20, E] 

Will make the following big element:
[20, A4, A2, E]

Can someone help me out?  I have to stick with lists as the structure
meaning I can't use tuples or dictionaries.

Thanks,
M