Reading ?expand.grid, there is a "see also" reference to "combn" which looks
close to what you want.
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Sent from my phone. Please excuse my brevity.
Q <quaga...@gmail.com> wrote:
Hello,
I'm trying to create a data frame where each row has a unique combination of
factors.
I start with a vector of species like so:
> 1> test <- c("A","B","C","D")
>
> 1> test
>
> [1] "A" "B" "C" "D"
>
To get all species combinations I have used expand.grid like this:
> 1> pairs <- expand.grid(test,test)
> 1> pairs
> Var1 Var2
> 1 A A
> 2 B A
> 3 C A
> 4 D A
> 5 A B
> 6 B B
> 7 C B
> 8 D B
> 9 A C
> 10 B C
> 11 C C
> 12 D C
> 13 A D
> 14 B D
> 15 C D
> 16 D D
>
Now I want to select only the unique pairs, which I have tried to do with
the function "unique":
> 1> unique(pairs)
>
, but that doesn't do anything... I guess because it considers A,B to be
different from B,A. The data frame I would like to end up with should look
like this.
> Var1 Var2
> 1 A A
> 2 B A
> 3 C A
> 4 D A
> 6 B B
> 7 C B
> 8 D B
> 11 C C
> 12 D C
> 16 D D
>
Thanks for your help!
Q
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