[R] Create unique sets of 3 from a vector of IDs?

[Dylan Beaudette]

On Tue, Dec 2, 2008 at 7:42 PM, philozine <philozine at yahoo.com> wrote:
> Dear all:
>
> This is one of those "should be easy" problems that I'm having great difficulty solving. I have a vector containing ID codes, and I need to generate a 3-column matrix that contains all possible combinations of three.
>
> For example, my ID vector looks like this:
> A
> B
> C
> D
> E
>
> I need to generate a matrix that looks like this:
> A B C
> A B D
> A B E
> A C B
> A C D
> A C E
> A D B
> A D C
> A D E

Hi,

Does this do what you want?

expand.grid(letters[1:5], letters[1:5], letters[1:5])


D


> .... and so on. (Yes, this could yield some very large matrices!) It's totally fine, though less desirable, if the resulting matrix contains combinations with "duplicates," e.g., A A A, A A B, or whatever.
>
> Thoughts? I'm pretty much stumped here. Thanks in advance for any help you can offer.
>
> Best regards,
>
> Brandon
>
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