R Function

Function is also an object, like in JavaScript

• Function is an object
• Function can be pass to another object
• No return keyword in function
• Function argument can be matched by name

Example:

add2 <- function(x, y){
    x + y
}

steps of improve function

x <- 1:20
above10 <- function(x){
    use <- x > 10
    x[use]
}
r <- above10(x)
print(r)

aboveN <- function(x, n){
    use <- x > n
    x[use]
}
r <- aboveN(x, 10)
print(r)

aboveN <- function(x, n=10){
    use <- x > n
    x[use]
}
r <- aboveN(x)
print(r)

Environment

• An environment is a collection of (symble, value) pairs.
• Every environment has a parent environment; it is possible an environment has muliply children.
• the only environment without parent is empty environment.
• A function + an environment = a closure or function closure.

Constructer Function

• the function construnction another function

make.power <- function(n) {
    pow <- function(x) {
        x^n
    }
    pow
}
square <- make.power(n=2)
cube <- make.power(3)
square(3) # 9
cube(3)  # 27

check environment

ls(environment(square))
# [1] "n"   "pow"
get('n', environment(square))
# [1] 2