[R] Union of list elements

[Pat Meyer]

Hi,

First of all, let me thank you all for replying so rapidly to my first 
question on this list. It was very very helpfull... and I'm learning R 
faster and faster.

I just encountered a second problem, which may also have a simple solution.

Here it is:

In my program, a vector is a set of objects.

I was looking for a way to store these sets in a big object. I chose to 
store them in a list.

So now I have a list of vectors which looks as follows:

[[1]]
[1] "a1" "a3" "a4"

[[2]]
[1] "a1" "a4" "a5"

[[3]]
[1] "a1" "a5" "a6"

Then comes a crucial step where I may have to add the vector ("a3", "a1", 
"a4") in this list.

But as you can see, this set is already present (at position 1 of my list). 
So it should not be added. If I do a systematic concatenation, at the end, I 
have a list with too many vectors (where some elements of my list represent 
the same set).

So what I would like to do is a type of Union, but I can't find a way to do 
it. Unions work only on vectors, and not a vector and a list of vectors.

Can anyone help me with this?

I thank you very much in advance

Patrick