Conditional expressions

It is common that the logic of a program is not perfectly sequential but contains several branches dependent on certain conditions. Therefore, one of the most basic constructs of a typical programming language is its conditional expressions. In R, if can be used to branch the logic flow by logical conditions.

Using if as a statement

Like many other programming languages, the if expression works with a logical condition. In R, a logical condition is represented by an expression producing a single-element logical vector. For example, we can write a simple function check_positive that returns 1 if a positive number is provided and nothing otherwise:

check_positive <- function(x) { 
  if (x > 0) { 
    return(1) 
  } 
} 

In the preceding function, x > 0 is the condition to check. If the condition is satisfied, then the function returns 1. Let's verify the function with various inputs:

check_positive(1)
## [1] 1
check_positive(0)

It seems that the function...