[R] min and max operations on matrix

[Gabor Grothendieck]

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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