On Dec 21, 2011, at 08:59 , Antje Niederlein wrote:
> Hi there,
>
> I have a vector and would like to create a data frame, which contains
> all unique combination of two elements, regardless of order.
>
> myVec <- c(1,2,3)
>
> what expand.grid does:
>
> 1,1
> 1,2
> 1,3
> 2,1
> 2,2
> 2,3
> 3,1
> 3,2
> 3,3
>
> what I would like to have
>
> 1,1
> 1,2
> 1,3
> 2,2
> 2,3
> 3,3
>
> Can anybody help?
I almost said combn(), but that won't give you the same element twice. So either
> rbind(cbind(1:3,1:3),t(combn(3,2)))
[,1] [,2]
[1,] 1 1
[2,] 2 2
[3,] 3 3
[4,] 1 2
[5,] 1 3
[6,] 2 3
or
> e <- expand.grid(1:3,1:3)
> e[e[,1]<=e[,2],]
Var1 Var2
1 1 1
4 1 2
5 2 2
7 1 3
8 2 3
9 3 3
or maybe
> subset(expand.grid(1:3,1:3),Var1 <= Var2)
Var1 Var2
1 1 1
4 1 2
5 2 2
7 1 3
8 2 3
9 3 3
--
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: [email protected] Priv: [email protected]
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