[R] Common R/S Idioms - Swapping Rows or Cols in a Matrix

[Giovanni Petris]

I would try something like

> A[c(s,r),] <- A[c(r,s),]

Giovanni

-- 

 __________________________________________________
[                                                  ]
[ Giovanni Petris                 GPetris at uark.edu ]
[ Department of Mathematical Sciences              ]
[ University of Arkansas - Fayetteville, AR 72701  ]
[ Ph: (479) 575-6324, 575-8630 (fax)               ]
[ http://definetti.uark.edu/~gpetris/              ]
[__________________________________________________]


> Is there an idiomatic way of swapping rows/cols in a Matrix?
> 
> The standard approach for swapping rows r and u:
> tmpRow = A[r,]
> A[r,] = A[u,]
> A[u,] = tmpRow
> 
> Robin Hankin (R-Octave help sheet maintainer) says:
> 
> [I would implement your three line solution (which works!) as follows:
> 
> swap <- function(a,m,n) {
>  tmp <- a[m]
>  a[m] <- a[n]
>  a[n] <- tmp
>  return(a)
> }
> 
> then use things like
> 
> x <- matrix(1:100,10,10)
> 
> x[ swap(1:10,5,6),]                #swaps rows  5&6
> x[,swap(1:10,5,6) ]                #swaps cols  5&6
> x[ swap(1:10,5,6),swap(1:10,5,6)]  #both together
> 
> ]
> 
> Anybody?

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