mmelissa0908的部落格

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.  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. 
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 

It is declaring the function g inside f that takes the parameter y. y is free variable so y is assign to a available value of x. It then declares z = 4, then returns x + g(x). If f(x) is called with x = 1 it would be 1 + 1 + 4 = 6.

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