Question

The Rescale01 function below maps/scales all items in a vector to a range from 0 to 1. (Also discussed in lecture slides).

Rescale01 <- function(x){

rng <- range(x,na.rm = TRUE)

(x-rng[1])/(rng[2] - rng[1])

}

The function doesn’t work when x contains +ve or –ve infinity (indicated in R as Inf and –Inf, respectively). For example, if x is

x <- c(-1,-5,3,5,-3,0,2,Inf,-Inf)

Rescale01(x) returns a vector containing

NaN NaN NaN NaN NaN NaN NaN NaN NaN

Rewrite the function Rescale01 so that -Inf is mapped to 0, and Inf is mapped to 1.

Hint:

• to check item in a vector is Inf, use is.infinite(x) & (x>0)
• to check item in a vector is -Inf, use is.infinite(x) & (x<0)
• Within the function, first thing you need to do is replace all Inf by the maximum value in the vector (considering only the valid items), and replace all –Inf by the minimum value in the vector (considering only the valid items)

Answer 1

Rescale01 <- function(x){
x[is.infinite(x) & (x>0)]=max(x[!is.infinite(x)])
x[is.infinite(x) & (x<0)]=min(x[!is.infinite(x)])
rng <- range(x,na.rm = TRUE)
(x-rng[1])/(rng[2] - rng[1])
}

: Rescale01 <- function(x){ x[is.infinite(x) & (x>0)]=max(x[!is.infinite(x)]) x[is.infinite(x) & (x<0)]=min(x[!is.infinite(x)]) rng <- range(x, na.rm = TRUE) (x-rng[1])/(rng[2] - rng[1]) : X <- c(-1,-5,3,5,-3,0,2,Inf,-Inf) Rescale01(x) 0.4 0 0.8 1. 0.2 0.5 0.7 1 0