R If Else

Basic if Statement

An if statement checks a single condition in parentheses; if that condition is TRUE, the code inside the curly braces runs, and if it's FALSE, R simply skips over it and continues with whatever comes next.

temperature <- 38
if (temperature > 37) {
  print("Fever detected")
}

Adding an else Branch

Pair if with else to provide an alternative block of code that runs only when the condition is FALSE. Together they guarantee that exactly one of the two branches executes.

temperature <- 36.5
if (temperature > 37) {
  print("Fever detected")
} else {
  print("Temperature normal")
}

Chaining Conditions with else if

To test several conditions in sequence, chain else if blocks between the first if and the final else. R checks each condition top to bottom and runs the first block whose condition is TRUE, ignoring the rest — so order the conditions from most specific to least specific.

score <- 82
if (score >= 90) {
  grade <- "A"
} else if (score >= 75) {
  grade <- "B"
} else if (score >= 60) {
  grade <- "C"
} else {
  grade <- "F"
}
print(grade)

ifelse() — the Vectorized Version