Using R for Numerical Analysis in Science and Engineering

Chapter 4Programming and functions

R is a full-fledged programming language, with standard programming constructs like conditional execution, loops, and subroutines (called functions in R). In this chapter we show how these constructs are implemented.

4.1 Conditional execution: if and ifelse

Computer programs can choose different computations depending on whether a logical condition evaluates to true or false. The relational operators in R that perform such evaluation are listed in Section 2.5. The logical operators are & (and), | (or), and ! (not).

The if statement operates on logical vectors of length 1. A formal construction is

if(condition 1) {
    result 1
  } else if (condition 2) {
    result 2
  } else {
    result 3
}

For example

 > x = -3 > if(x ...