[R] how to use a matrix as an index to another matrix?
Linus Chen
||nu@@|@chen @end|ng |rom gm@||@com
Mon Oct 28 21:47:35 CET 2019
Hi Jinsong,
In such a case I think explicit loop IS the most elegant solution.
for(i in 1:2) A[,i] <- A[,i][B[,i]]
Linus
On Fri, 11 Oct 2019 at 11:44, Jinsong Zhao <jszhao using yeah.net> wrote:
>
> Hi there,
>
> I have two matrices, A and B. The columns of B is the index of the
> corresponding columns of A. I hope to rearrange of A by B. A minimal
> example is following:
>
> > set.seed(123)
> > A <- matrix(sample(1:10), nrow = 5)
> > B <- matrix(c(sample(1:5), sample(1:5)), nrow =5, byrow = FALSE)
> > A
> [,1] [,2]
> [1,] 3 9
> [2,] 10 1
> [3,] 2 7
> [4,] 8 5
> [5,] 6 4
> > B
> [,1] [,2]
> [1,] 2 1
> [2,] 3 4
> [3,] 1 5
> [4,] 4 3
> [5,] 5 2
> > A[,1] <- A[,1][B[,1]]
> > A[,2] <- A[,2][B[,2]]
> > A
> [,1] [,2]
> [1,] 10 9
> [2,] 2 5
> [3,] 3 4
> [4,] 8 7
> [5,] 6 1
>
> My question is whether there is any elegant or generalized way to replace:
>
> > A[,1] <- A[,1][B[,1]]
> > A[,2] <- A[,2][B[,2]]
>
> Thanks in advance.
>
> PS., I know how to do the above thing by loop.
>
> Best,
> Jinsong
>
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