Re: [R] Vectorize rearrangement within each column

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Fri 19 Jan 2007 - 12:41:35 GMT

Turn each matrix into a data.frame and then use mapply with the "[" function, converting back to matrix when done:

as.matrix(mapply("[", as.data.frame(ma), as.data.frame(idx)))

     V1 V2

[1,] 10 14
[2,] 12 15
[3,] 11 13


On 1/19/07, Osorio Roberto <roboso@gmail.com> wrote:
> Consider a matrix like
>
> > ma = matrix(10:15, nr = 3)
> > ma
> [,1] [,2]
> [1,] 10 13
> [2,] 11 14
> [3,] 12 15
>
> I want to rearrange each column according to row indexes (1 to 3)
> given in another matrix, as in
>
> > idx = matrix(c(1,3,2, 2,3,1), nr = 3)
> > idx
> [,1] [,2]
> [1,] 1 2
> [2,] 3 3
> [3,] 2 1
>
> The new matrix mb will have for each column the corresponding column
> of ma indexed by the corresponding column of idx, as in
>
> > mb = ma
> > for (j in 1:2) mb[,j] = ma[idx[,j], j]
> > mb
> [,1] [,2]
> [1,] 10 14
> [2,] 12 15
> [3,] 11 13
>
> Can I avoid the for() loop? I'm specially interested to find out if a
> fast implementation using lapply() would be feasible for large input
> matrices (analogues of ma and idx) transformed into data frames.
>
> Roberto Osorio
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri Jan 19 23:48:10 2007

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Fri 19 Jan 2007 - 13:30:27 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.