Using R and RStudio for Data Management, Statistical Analysis, and Graphics, 2nd Edition

i

i

“K23166” — 2015/1/28 — 9:35 — page 45 — #71

i

i

i

i

i

i

Chapter 4

Programming and operating

system interface

This chapter reviews programming functions as well as interactions with the underlying

operating system.

4.1 Control flow, programming, and data generation

4.1.1 Looping

Example: 11.2

x = numeric(k) # create placeholder

for (i in 1:length(x)) {

x[i] = rnorm(1) # this is slow and inefficient!

}

or (preferably)

x = rnorm(k) # this is far better

Note: Most tasks in R that could be written as a loop are often dramatically faster if they

are encoded as a vector operation (as in the second and preferred option above). Examples

of situations where loops are particularly ...