[R] "flipping" vector and matrix

Katharine Mullen
Tue, 23 Oct 2007 14:26:28 -0000

One way:

> x<-1:9
> rev(x)
[1] 9 8 7 6 5 4 3 2 1

for x as the matrix you gave:
> x
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    4    5    6
[3,]    7    8    9
>
>
> apply(t(x),1,rev)
     [,1] [,2] [,3]
[1,]    7    8    9
[2,]    4    5    6
[3,]    1    2    3


On Tue, 23 Oct 2007, Rainer M Krug wrote:

> Hi
>
> I have a vector
>
> x <- c(1, 2, 3, 4, 5)
>
> and I want to "flip" it around, i.e. I need
>
> 5, 4, 3, 2, 1
>
> Is there a ssolution apart from
>
> y <- x[length(x):1]
>
>
> I am also looking for the same for a matrix M, i.e.
>
> 1 2 3
> 4 5 6
> 7 8 9
>
> should become
>
> 7 8 9
> 4 5 6
> 1 2 3
>
> again, I am using
>
> M[1:dim(M)[1], dim(M)[2]:1]
>
>
> Thanks
>
> Rainer
>
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