Quiz 2.md

####Question 1 Suppose I define the following function in R

cube <- function(x, n) {
        x^3
}

What is the result of running

cube(3)

in R after defining this function? Your Answer Score Explanation An error is returned because 'n' is not specified in the call to 'cube' The number 27 is returned Correct 1.00 Because 'n' is not evaluated, it is not needed even though it is a formal argument. The users is prompted to specify the value of 'n'. A warning is given with no value returned.

####Question 2 The following code will produce a warning in R.

x <- 1:10
if(x > 5) {
        x <- 0
}

Why?

The expression uses curly braces. You cannot set 'x' to be 0 because 'x' is a vector and 0 is a scalar. 'x' is a vector of length 10 and 'if' can only test a single logical statement. Correct 1.00 There are no elements in 'x' that are greater than 5 The syntax of this R expression is incorrect.

####Question 3 Consider the following function

f <- function(x) {
        g <- function(y) {
                y + z
        }
        z <- 4
        x + g(x)
}

If I then run in R

z <- 10
f(3)

What value is returned?

10 Correct 1.00 7 4 16

####Question 4 Consider the following expression:

x <- 5
y <- if(x < 3) {
        NA
} else {
        10
}

What is the value of 'y' after evaluating this expression?

NA 10 Correct 1.00 5 3

####Question 5 Consider the following R function

h <- function(x, y = NULL, d = 3L) {
        z <- cbind(x, d)
        if(!is.null(y))
                z <- z + y
        else
                z <- z + f
        g <- x + y / z
        if(d == 3L)
                return(g)
        g <- g + 10
        g
}

Which symbol in the above function is a free variable?

f z d L g

####Question 6 What is an environment in R?

a list whose elements are all functions an R package that only contains data a special type of function a collection of symbol/value pairs Correct 1.00

####Question 7 The R language uses what type of scoping rule for resolving free variables?

dynamic scoping global scoping compilation scoping lexical scoping Correct 1.00

####Question 8 How are free variables in R functions resolved?

The values of free variables are searched for in the working directory The values of free variables are searched for in the environment in which the function was called The values of free variables are searched for in the global environment The values of free variables are searched for in the environment in which the function was defined Correct 1.00

####Question 9 What is one of the consequences of the scoping rules used in R?

All objects can be stored on the disk All objects must be stored in memory Correct 1.00 R objects cannot be larger than 100 MB Functions cannot be nested

####Question 10 In R, what is the parent frame?

It is the package search list It is the environment in which a function was defined Inorrect 0.00 It is the environment in which a function was called It is always the global environment