[R] min and max operations on matrix
Gabor Grothendieck
ggrothendieck at gmail.com
Wed Jan 20 21:05:36 CET 2010
Try this:
> t(apply(x, 1, function(x) (x == max(x)) - (x == min(x))))
[,1] [,2] [,3]
[1,] -1 0 1
[2,] 1 -1 0
[3,] 1 0 -1
You can avoid the transpose using plyr:
> library(plyr)
> aaply(x, 1, function(x) (x == max(x)) - (x == min(x)))
Var1 1 2 3
1 -1 0 1
2 1 -1 0
3 1 0 -1
On Wed, Jan 20, 2010 at 11:57 AM, <Murali.MENON at fortisinvestments.com> wrote:
> Folks,
>
> I've got a matrix x as follows:
>
>> x <- matrix(c(1,2,3,5,3,4,3,2,1), ncol = 3, byrow = TRUE)
>> x
> [,1] [,2] [,3]
> [1,] 1 2 3
> [2,] 5 3 4
> [3,] 3 2 1
>
>
> In each row of x, I want to replace the minimum value by -1, the maximum
> value by +1 and all other values by 0.
>
> So in the above case I want to end up as follows:
>
> [,1] [,2] [,3]
> [1,] -1 0 1
> [2,] 1 -1 0
> [3,] 1 0 -1
>
> I tried the following, which seems to work:
>
>> t(apply(x, 1, function(y) {z <- numeric(NROW(y)); z[which.min(y)] <-
> -1; z[which.max(y)]<- 1; z}))
>
> Is there a neater way to do this?
>
> Thanks,
>
> Murali
>
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