R Functions

Why write your own functions

As scripts grow, you'll often find yourself repeating very similar chunks of code with just a few values changed. Wrapping that logic in a function lets you write it once, give it a clear name, and reuse it anywhere, which cuts down on copy-paste mistakes and makes your script easier to read at a glance.

greet <- function(name) {
  paste("Hello,", name)
}

greet("Asha")
greet("Ravi")

The parts of a function

• Name: the identifier you use to call the function later, such as greet
• function(...) keyword: marks the start of a function definition and lists its parameters
• Body: the block of code in curly braces that runs each time the function is called
• Return value: the result the function produces, which you can store, print, or use in further calculations

R doesn't always require the word return. If the last line of a function's body is an expression, R automatically returns its value. Writing return(value) explicitly is still useful when you want to exit a function early, before reaching its last line.

classify <- function(score) {
  if (score < 0) {
    return("invalid")  # exits early
  }
  if (score >= 60) "pass" else "fail"  # last expression is returned automatically
}

classify(75)
classify(-5)

Reusing a function across many inputs

circle_area <- function(radius) {
  pi * radius^2
}

circle_area(1)
circle_area(2.5)
circle_area(10)

Variable scope inside a function

Variables created inside a function's body are local to that function, they exist only while the function is running and disappear once it finishes. This means a variable named total inside one function won't clash with a different total defined outside it or in another function, which keeps functions self-contained and easier to reason about.