# [R] efficient way to replace a range of numeric with a integer in a matrix

Jinsong Zhao jszhao at yeah.net
Mon Aug 11 23:40:05 CEST 2014

```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

```

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