Re: [R] all possible combinations of list elements

From: Marc Schwartz <MSchwartz_at_mn.rr.com>
Date: Wed 04 Jan 2006 - 12:04:14 EST

On Tue, 2006-01-03 at 18:57 -0600, Eberhard F Morgenroth wrote:
> I have a list as follows
>
> P <- list(A = c("CS", "CX"),
> B = 1:4,
> Y = c(4, 9))
>
> I now would like to prepare a new list where the rows of the new list
> provide all possible combinations of the elements in the orginal list.
> Thus, the result should be the following
>
> CS 1 4
> CS 1 9
> CS 2 4
> CS 2 9
> CS 3 4
> CS 3 9
> CS 4 4
> CS 4 9
> CX 1 4
> CX 1 9
> CX 2 4
> CX 2 9
> CX 3 4
> CX 3 9
> CX 4 4
> CX 4 9
>
> Is there a simple routine in R to create this list of all possible
> combinations? The routine will be part of a function with the list "P"
> as an input. "P" will not always have the same number of elements and
> each element in the list "P" may have different numbers of values.

See ?expand.grid

> expand.grid(P)

    A B Y
1 CS 1 4
2 CX 1 4
3 CS 2 4
4 CX 2 4
5 CS 3 4
6 CX 3 4
7 CS 4 4
8 CX 4 4
9 CS 1 9
10 CX 1 9
11 CS 2 9
12 CX 2 9
13 CS 3 9
14 CX 3 9
15 CS 4 9
16 CX 4 9

HTH, Marc Schwartz



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