Quiz_2.md

Quiz 2

Attempts	Score
2/3	10/10

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?

Answer

The number 27 is returned

Explanation

Because 'n' is not evaluated, it is not needed even though it is a formal argument.

> cube <- function(x, n) {
+     x^3
+ }
> cube(3)
[1] 27

Question 2

The following code will produce a warning in R.

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

Why?

Answer

'x' is a vector of length 10 and 'if' can only test a single logical statement.

Explanation

> if(x > 5) {
+     x <- 0
+ }
Warning message:
In if (x > 5) { :
  the condition has length > 1 and only the first element will be used

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?

Answer

10

Explanation

> f <- function(x) {
+     g <- function(y) {
+         y + z
+     }
+     z <- 4
+     x + g(x)
+ }
> z <- 10
> f(3)
[1] 10

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?

Answer

10

Explanation

> x <- 5
> y <- if(x < 3) {
+     NA
+ } else {
+     10
+ }
> y
[1] 10

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?

Answer

f

Explanation

A free variable is a variable that is not defined in the function nor an argument of the function.

Question 6

What is an environment in R?

Answer

a collection of symbol/value pairs

Question 7

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

Answer

lexical scoping

Question 8

How are free variables in R functions resolved?

Answer

The values of free variables are searched for in the environment in which the function was defined

Question 9

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

Answer

All objects must be stored in memory

Question 10

In R, what is the parent frame?

Answer

It is the environment in which a function was called