efficient way to replace a range of numeric with a integer in a matrix

You can use
     m[m > 0 & m <= 1.0] <- 1
     m[m > 1 ] <- 2
or, if you have lots of intervals, something based on findInterval().  E.g.,
     m[] <- findInterval(m, c(-Inf, 0, 1, Inf)) - 1

(What do you want to do with non-positive numbers?)

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Aug 11, 2014 at 2:40 PM, Jinsong Zhao <jszhao at yeah.net> wrote:

Hi there,

I hope to replace a range of numeric in a matrix with a integer. For
example, in the following matrix, I want to use 1 to replace the elements
range from 0.0 to 1.0, and all larger than 1. with 2.

(m <- matrix(runif(16, 0, 2), nrow = 4))

           [,1]       [,2]      [,3]     [,4]
[1,] 0.7115088 0.55370418 0.1586146 1.882931
[2,] 0.9068198 0.38081423 0.9172629 1.713592
[3,] 1.5210150 0.93900649 1.2609942 1.744456
[4,] 0.3779058 0.03130103 0.1893477 1.601181

so I want to get something like:

      [,1] [,2] [,3] [,4]
[1,]    1    1    1    2
[2,]    1    1    1    2
[3,]    2    1    2    2
[4,]    1    1    1    2

I wrote a function to do such thing:

fun <- function(x) {
     if (is.na(x)) {
         NA
     } else if (x > 0.0 && x <= 1.0) {
         1
     } else if (x > 1.0) {
         2
     } else {
         x
     }
}

Then run it as:

apply(m,2,function(i) sapply(i, fun))

However, it seems that this method is not efficient when the dimension is
large, e.g., 5000x5000 matrix.

Any suggestions? Thanks in advance!

Best regards,
Jinsong