Math0: R Functions

First, we define a function \(f(x,y)=x+2y\) and play around with it. We assign \(y=1\) so that we can use either one or two arguments for the function. Note that reassign values of \(x, y\) won't affect the function in any way. See the following code and output:

> f <- function(x,y=1) {x+2*y} > f(1,2) [1] 5 > f(1) [1] 3 > f(1) [1] 3 > f(1,2) [1] 5 > x<-1 > y<-1 > f(1,2) [1] 5 > f(1) [1] 3 > (function(x) {x^2}) (3) [1] 9

Exception handling - first example:

openfile<-function(filename){ if (file.exists(filename)){ read.delim(filename) } else { stop("No such file or permission denied: ",filename) } }

A modified version and output (the case that the file exist)

> openfile<-function(filename){ + if (file.exists(filename)){ + "Ha! I find it!!" + } else { + stop("No such file or permission denied: ",filename) + + } + } > openfile("E:/Software/Software - Math/R/Books/Rnut0.txt") [1] "Ha! I find it!!"

Anonymous Function

> eval.at.2<-function(f){f(2)} > eval.at.2(function(x){x^3}) [1] 8

Example: apply function to an array. See the following code and output.

> eval.at.2<-function(f){f(2)} > a <- c(1:5) > sapply(a,function(x) {x^2}) [1] 1 4 9 16 25 > b <- NULL > for (i in 1:length(a)) {b[i]<-a[i]^2} > b [1] 1 4 9 16 25

Last modified: Wednesday, 18 June 2014, 9:21 AM