if / else

if / else

An if statement runs a block only when its condition is TRUE; an optional else runs otherwise. The condition must evaluate to a single logical value, not a vector -- using a vector condition triggers an error or warning depending on the R version. else must appear on the same line as the closing brace of the if block when written across multiple lines.

Warning: The condition in if() must be a single TRUE/FALSE value, not a vector -- use ifelse() or all()/any() for vectorized conditions.

Example: if / else

score <- 85

if (score >= 90) {
  cat("Grade: A\n")
} else if (score >= 70) {
  cat("Grade: B\n")
} else {
  cat("Grade: C\n")
}