Well-Behaved Functions – Exercises

Exercise 1
Write a function that calculates number a to the power of b, but let b have a default value of 2.

Exercise 2
Re-write the function from exercise 1 so that a has a default value of b+1 already from the formals (from the argument definition.)

Exercise 3
Write a function div() that checks if the first number divides the second.

Exercise 4
Write an infix function %div% that checks if the left-hand side divides the right-hand side. # Example 3 %div% 42 [1] TRUE 3 %div% 13 [1] FALSE

Exercise 5
Write a function that changes the value of pi in the R global environment to whatever you specify as the argument. Note: it is not recommended to re-define the value of “pi” in a real-life R program.
# Example pi [1] 3.141593 chpi(4) pi [1] 4 chpi("I like cats") pi [1] "I like cats"

Exercise 6
Write an infix (binary) function that checks if the left hand side (lhs) is in the range between the maximum and minimum of the rhs.
set.seed(1) rnorm(6) %betw% c(-1, 1) [1] TRUE TRUE TRUE FALSE TRUE TRUE

Exercise 7
Write another infix operator that pastes two strings and uses it in a function that takes ellipsis. Now, call the function and feed it two strings and concatenate them to produce some text.

Exercise 8
What did you think about the example in exercise 3? What does the following code (from the book Advanced R) return?
f2 <- function(x = z) { z <- 100 x } f2()

Exercise 9
Write a function that creates a function analogous to the one from exercise 1 by feeding 2 as an argument. Note: this is not a typo.
# Example of a function called power() powerof2 <- power(2) powerof2(3) [1] 9

Exercise 10
Make a new names<- (replacement) function called names2<- that also allows you to update the names of data structures, except it forces the names it is given to all-lowercase.
# Example x <- 3:4 names2(x) <- c("IMPORTANT", "For The CAT do NOT EAT") x important for the cat do not eat 3 4

(Photo by Pascal)