R (Programming Language) LinkedIn Skill Assessment Answer

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

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

Q2. What value does this statement return?

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

1. 1
2. 365✔️
3. 4
4. 12

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

1. remove()✔️
2. erase()
3. detach()
4. delete()

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

xvect<-c(1,2,3)
xvect[2] <- "2"
xvect

1. [1] 1 2 3
2. [1] "1" 2 "3"
3. [1] "1" "2" "3"✔️
4. [1] 7 9

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

1. height(length(height))
2. height[length(height)]✔️
3. height[length[height]]
4. 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?

1. sample with replacement
2. population
3. trimmed sample
4. sample <– not sure✔️

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

1. Var_A!
2. _VarA
3. .2Var_A
4. Var2_A✔️

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

1. A matrix has two dimensions, while an array can have three or more dimensions.✔️
2. An array is a subtype of the data frame, while a matrix is a separate type entirely.
3. A matrix can have columns of different lengths, but an array’s columns must all be the same length.
4. 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?

1. type
2. length
3. attributes
4. 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?

1. StDf[1:2,-3]
2. StDf[1:2,1]✔️
3. StDf[1:2,]
4. StDf[1,2,]

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

1. BOF(pizza, 5)
2. first(pizza, 5)
3. top(pizza, 5)
4. 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?

1. console(-25)
2. console(reverse=TRUE)
3. history()
4. 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"

1. class( d.pizza( , "temperature" ) )
2. class( d.pizza[ , "temperature" ] )
3. class( d.pizza$temperature )
4. 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. [1] NaN
2. [1] -4
3. [1] 4 -1 -1 2
4. [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)

1. No, y’s new class is "array".
2. Yes, y’s new class is "matrix".✔️
3. No, y’s new class is "vector".
4. 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)

1. list
2. string
3. factor
4. character vector✔️

Q17. How does a vector differ from a list?

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

Q18. What statement shows the objects on your workspace?

1. list.objects()
2. print.objects()
3. getws()
4. ls()✔️

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

1. rbind()
2. cbind()✔️
3. bind()
4. 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] 1 2 4 5
2. "C"
3. [1] "1" "2" "C" "4" "5"✔️
4. [1] 1 2 C 4 5

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

x <- NA
y <- x/1

1. Inf
2. Null
3. NaN
4. 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?

1. cor.test(Var1 ~ Var2)
2. cor.test(mydata$(Var1,Var2))
3. cor.test(mydata$Var1,mydata$Var2)✔️
4. 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)

1. attach(d.pizza)✔️
2. summarize(deliver)
3. mean <- rbind(d.pizza,count)
4. deliver[!complete.cases(deliver),]

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

1. data frame: names() and rownames() matrix: colnames() and row.names()
2. data frame: names() and row.names() matrix: dimnames() (not sure)✔️
3. data frame: colnames() and row.names() matrix: names() and rownames()
4. 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)

1. records where the first character is a C
2. any record with a value containing a C
3. TRUE or FALSE, depending on whether any character in ournames is C
4. TRUE and 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

1. ""✔️
2. d
3. NULL
4. NA

Q28. Which of the following statements doesn’t yield the code output below. Review the following code. What is the result of line 3?

x <- c(1, 2, 3, 4)
Output: [1] 2 3 4

1. x[c(2, 3, 4)]
2. x[-1]
3. x[c(-1, 0, 0, 0)]
4. x[c(-1, 2, 3, 4)]✔️

Q29. Given DFMerged <- merge(DF1, DF2) and the image below, how manu rows are in DFMerged?

DF1(data frame 1): DF2(data frame 2):
VarA VarB VarA VarD
1 1 2 1 18 21
2 4 5 2 19 22
3 7 8 3 20 23

1. 6
2. 9
3. 3
4. 0✔️

Q30. What does R return in response to the final statement?

x<-5:8
names(x)<-letters[5:8]
x

1. e f g h
   "5" "6" "7" "8"
2. 5 6 7 8
3. e f g h
4. e f g h 5 6 7 8✔️

Q31. How do you return "October" from x in this code?

x<-as.Date("2018-10-01")

1. attr()
2. months(x)✔️
3. as.month(x)
4. month(x)

Q32. How will R respond to the last line of this code?

fact<-factor(c("Rep","Dem","Dem","Rep"))
fact
[1] Rep Dem Dem Rep
Levels: Rep Dem
fact[2]<-"Ind"

1. >
2. [,2]Ind
3. invalid factor level, NA generated✔️
4. Ind

Q33. What does R return?

StartDate<- as.Date("2020/2/28")
StopDate<- as.Date("2020/3/1")
StopDate-StartDate

1. "1970-01-02"
2. time difference of one day
3. time difference of two days✔️
4. error in x-y: nonnumeric argument to binary operator

Q34. What does the expression mtrx * mtrx do ?

> mtrx <- matrix( c(3,5,8,4), nrow= 2,ncol=2,byrow=TRUE)
> newmat <- mtrx * mtrx

1. it transpose mtrx
2. it premultiplies the current netwmat row by the newmat column.
3. it returns the results of a matrix multiplication✔️
4. It squares each cell in mtrx

Q35. Which function in R combines differents values into a single object?

1. connect()
2. concat()
3. contact()
4. c()✔️

Q36. Which file contains settings that R uses for all users of a given installation of R?

1. Rdefaults.site
2. Renviron.site
3. Rprofile.site✔️
4. Rstatus.site

Q36. If mdf is a data frame, which statement is true ?

1. ncol(mdf) equals length(mdf)✔️.
2. The number of rows must equals the number of columns.
3. The legnth of any column in mdf may differ from any other column in mdf
4. All columns must have the same data type.

Q37. A list can contain a list as an element. MyList has five columns, and the third column’s item is a list of three items. How do you put all seven values in MyList into a single vector?

1. vector(MyList, length = 7)
2. coerce(MyList, nrows = 1)
3. unlist(MyList)✔️
4. coerce(MyList, nrows = 7)

Q38. Which strings could be returned by the function ls(path = "^V")?

1. ANOVAData, anovadata
2. VisitPCA, VarX✔️
3. VisitPCA, varx
4. Xvar, Yvar

Q39. Which strings could be returned by the function ls(path = "^V")?

1. ANOVAData, anovadata
2. VisitPCA, VarX✔️
3. VisitPCA, varx
4. Xvar, Yvar