Functions

Code

# Basic function
square <- function(x) x^2
print(square(5))

# Default arguments
greet <- function(name = "world", greeting = "Hello") {
  paste(greeting, name, sep = ", ")
}
print(greet())
print(greet("Alice"))
print(greet("Bob", "Hi"))

# Named and partial matching
f <- function(a, b, c) a + b + c
print(f(c = 3, 1, 2))

# Variable arguments
concat <- function(..., sep = " ") {
  paste(..., sep = sep)
}
print(concat("a", "b", "c"))
print(concat("a", "b", "c", sep = "-"))

# Return value (last expression or explicit)
sign_num <- function(x) {
  if (x > 0) return("positive")
  if (x < 0) return("negative")
  "zero"
}
print(sign_num(-3))

# Closures
counter <- function() {
  n <- 0
  list(
    inc = function() { n <<- n + 1; n },
    get = function() n
  )
}
cnt <- counter()
print(cnt$inc())
print(cnt$inc())
print(cnt$get())

# Anonymous functions in sapply
print(sapply(1:5, function(n) n^3))

# Function as argument
apply_twice <- function(f, x) f(f(x))
print(apply_twice(function(x) x + 1, 5))

Explanation

R functions are first-class objects: they can be assigned, passed as arguments, and returned from other functions. Default arguments, named calls, and the dots (...) let you write flexible APIs. Closures capture their enclosing environment, allowing stateful factories like the counter example using the <<- super-assignment operator.

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