R Programming Assessment Answers

R Programming Language Assessment LinkedIn Questions and Answers 2021

Q1. How does a matrix differ from a data frame?

A matrix may contain numeric values only.
A matrix must not be singular.
A data frame may contain variables that have different modes.
A data frame may contain variables of different lengths.

Q2. What value does this statement return?

unclass(as.Date("1971-01-01"))

1
365
4
12

Q3. What do you use to take an object such as a data frame out of the workspace?

remove()
erase()
detach()
delete()

Q4. Review the following code. What is the result of line 3?

xvect<-c(1,2,3)

xvect[2] <- "2"

xvect

[1] 1 2 3
[1] "1" 2 "3"
[1] "1" "2" "3"
[1] 7 9

Q5. The variable height is a numeric vector in the code below. Which statement returns the value 35?

height(length(height))
height[length(height)]
height[length[height]]
height(5)

Q6. In the image below, the data frame is named rates. The statement sd(rates[, 2]) returns 39. As what does R regard Ellen's product ratings?

sample with replacement
population
trimmed sample
sample <-- not sure

Q7. Which choice does R regard as an acceptable name for a variable?

Var_A!
\_VarA
.2Var_A
Var2_A

Q8. What is the principal difference between an array and a matrix?

A matrix has two dimensions, while an array can have three or more dimensions.
An array is a subtype of the data frame, while a matrix is a separate type entirely.
A matrix can have columns of different lengths, but an array's columns must all be the same length.
A matrix may contain numeric values only, while an array can mix different types of values.

Q9. Which is not a property of lists and vectors?

type
length
attributes
scalar

Q10. In the image below, the data frame on lines 1 through 4 is names StDf. State and Capital are both factors. Which statement returns the results shown on lines 6 and 7?

StDf[1:2,-3]
StDf[1:2,1]
StDf[1:2,]
StDf[1,2,]

Q11. Which function displays the first five rows of the data frame named pizza?

BOF(pizza, 5)
first(pizza, 5)
top(pizza, 5)
head(pizza, 5)

Q12. You accidentally display a large data frame on the R console, losing all the statements you entered during the current session. What is the best way to get the prior 25 statements back?

console(-25)
console(reverse=TRUE)
history()
history(max.show = 25)

Q13. d.pizza is a data frame. It's column named temperature contains only numbers. If u extract temperature using the [] accessors, its class defaults to numeric. How can you access temperature so that it retains the class of data.frame?

> class( d.pizza[ , "temperature" ] )

> "numeric"

class( d.pizza( , "temperature" ) )
class( d.pizza[ , "temperature" ] )
class( d.pizza$temperature )
class( d.pizza[ , "temperature", drop=F ] )

Q14. What does c contain?

a <- c(3,3,6.5,8)

b <- c(7,2,5.5,10)

c <- a < b

[1] NaN
[1] -4
[1] 4 -1 -1 2
[1] TRUE FALSE FALSE TRUE

Q15. Review the statements below. Does the use of the dim function change the class of y, and if so what is y's new class?

> y <- 1:9

> dim(y) <- c(3,3)

No, y's new class is "array".
Yes, y's new class is "matrix".
No, y's new class is "vector".
Yes, y's new class is "integer".

Q16. What is mydf$y in this code?

mydf <- data.frame(x=1:3, y=c("a","b","c"), stringAsFactors=FALSE)

list
string
factor
character vector

Q17. How does a vector differ from a list?

Vectors are used only for numeric data, while list are useful for both numeric and string data.
Vectors and lists are the same thing and can be used interchangeably.
A vector contains items of a single data type, while a list can contain items of different data types.
Vectors are like arrays, while lists are like data frames.

Q18. What statement shows the objects on your workspace?

list.objects()
print.objects()
getws()
ls()

Q19. What function joins two or more column vectors to form a data frame?

rbind()
cbind()
bind()
coerce()

Q20. Review line 1 below. What does the statement in line 2 return?

1 mylist <- list(1,2,"C",4,5)

2 unlist(mylist)

[1] 1 2 4 5
"C"
[1] "1" "2" "C" "4" "5"
[1] 1 2 C 4 5

Q21. What is the value of y in this code?

x <- NA

y <- x/1

Inf
Null
NaN
NA

Q22. Two variable in the mydata data frame are named Var1 and Var2. How do you tell a bivariate function, such as cor.test, which two variables you want to analyze?

cor.test(Var1 ~ Var2)
cor.test(mydata$(Var1,Var2))
cor.test(mydata$Var1,mydata$Var2)
cor.test(Var1,Var2, mydata)

Q23. A data frame named d.pizza is part of the DescTools package. A statement is missing from the following R code and an error is therefore likely to occur. Which statement is missing?

library(DescTools)

deliver <- aggregate(count,by=list(area,driver), FUN=mean)

print(deliver)

attach(d.pizza)
summarize(deliver)
mean <- rbind(d.pizza,count)
deliver[!complete.cases(deliver),]

Q24. How to name rows and columns in DataFrames and Matrices F in R?

data frame: names() and rownames() matrix: colnames() and row.names()
data frame: names() and row.names() matrix: dimnames() (not sure)
data frame: colnames() and row.names() matrix: names() and rownames()
data frame: colnames() and rownames() matrix: names() and row.names()

Q25. Which set of two statements-followed by the cbind() function-results in a data frame named vbound?

[ ] v1<-list(1,2,3)

v2<-list(c(4,5,6))

vbound<-cbind(v1,v2)

[ ] v1<-c(1,2,3)

v2<-list(4,5,6))

vbound<-cbind(v1,v2)

[ ] v1<-c(1,2,3)

v2<-c(4,5,6))

vbound<-cbind(v1,v2)

Q26. ournames is a character vector. What values does the statement below return to Cpeople?

Cpeople <- ournames %in% grep("^C", ournames, value=TRUE)

records where the first character is a C
any record with a value containing a C
TRUE or FALSE, depending on whether any character in ournames is C
TRUE or FALSE values, depending on whether the first character in an ournames record is C

Q27. What is the value of names(v[4])?

v <- 1:3

names(v) <- c("a", "b", "c")

v[4] <- 4