[R] Help with matrix manipulation

[Simon Blomberg]

apply is your friend:

fn <- function (x, a, b) {
    if (x < a) return(a) else
    if (x > b) return(b) else
    x
    }

apply(mat, c(1,2), fn, -4, 3)

     [,1] [,2] [,3] [,4]
[1,]   -4   -1    3   -4
[2,]   -4    0    3   -3
[3,]   -3    1    3   -2
[4,]   -2    2   -4   -1

HTH,

Simon.

Kartik Pappu wrote:
> Hi all,
>
> I have a square (a x a) matrix with values in a range. For example:
>
>       [,1] [,2] [,3] [,4]
> [1,]   -5   -1    3   -4
> [2,]   -4    0    4   -3
> [3,]   -3    1    5   -2
> [4,]   -2    2   -5   -1
>
> I want to take any number smaller than -4 (in this example -5) and
> replace it with -4 and similarly take any number greater than 3 (in
> this case 4 and 5) and replace it with 3. The other numbers (and the
> overall structure of the matrix should remain unchanged.
>
> Seems like something that would use an "if a<b then c else d" kind of
> logic, but I cannot figure out how to manipulate the entire matrix.
>
> Thanks much
>
> Kartik
>
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>   
-- 
Simon Blomberg, B.Sc.(Hons.), Ph.D, M.App.Stat.
Centre for Resource and Environmental Studies
The Australian National University
Canberra ACT 0200
Australia
T: +61 2 6125 7800 email: Simon.Blomberg_at_anu.edu.au
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