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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