R (Programming Language)  LinkedIn Skill Assessments Quizzes with Answers
R (Programming Language)
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("19710101"))
 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 named 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 a column named temperature contains only numbers. If you 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 lists 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 statementsfollowed by the cbind() functionresults 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 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
 ""
 d
 NULL
 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
 x[c(2, 3, 4)]
 x[1]
 x[c(1, 0, 0, 0)]
 x[c(1, 2, 3, 4)]
Q29. Given DFMerged < merge(DF1, DF2) and the image below, how manu rows are in DFMerged?
 6
 9
 3
 0
Q30. What does R return in response to the final statement?
x<5:8
names(x)<letters[5:8]
x
 e f g h “5” “6” “7” “8”
 5 6 7 8
 e f g h
 e f g h 5 6 7 8
Q31. How do you return “October” from x in this code?
x<as.Date("20181001")
 attr()
 months(x)
 as.month(x)
 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"
 >
 [,2]Ind
 invalid factor level, NA generated
 Ind
Q33. What does R return?
StartDate< as.Date("2020/2/28")
StopDate< as.Date("2020/3/1")
StopDateStartDate
 “19700102”
 time difference of one day
 time difference of two days
 error in xy: 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
 it transpose mtrx
 it premultiplies the current netwmat row by the newmat column.
 it returns the results of a matrix multiplication
 It squares each cell in mtrx
Q35. Which function in R combines different values into a single object?
 connect()
 concat()
 contact()
 c()
Q36. Which file contains settings that R uses for all users of a given installation of R?
 Rdefaults.site
 Renviron.site
 Rprofile.site
 Rstatus.site
Q36. If mdf is a data frame, which statement is true ?
 ncol(mdf) equals length(mdf).
 The number of rows must equals the number of columns.
 The legnth of any column in mdf may differ from any other column in mdf
 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?
 vector(MyList, length = 7)
 coerce(MyList, nrows = 1)
 unlist(MyList)
 coerce(MyList, nrows = 7)
Q38. Which strings could be returned by the function ls(path = “^V”)?
 ANOVAData, anovadata
 VisitPCA, VarX
 VisitPCA, varx
 Xvar, Yvar
Q39. StDf is a data frame. Based on this knowledge, what does this statement return?
StDf[, 1]
 all but the first row and first column of StDf
 all but the final column of StDf
 all but the first column of StDf
 only the first column of StDf
Q40. Which statement enables you to interactively open a single file?
 file.list()
 file.select()
 file.choose()
 file.open()
Q41. How are these data types alike: logical, integer, numeric, and character?
 Each is a type of data frame.
 Each is a type of atomic vector.
 Each is a type of complex vector.
 Each is a type of raw vector.
Q42. What does the MyMat[ ,3]
subsetting operation return for this code?
MyMat = matrix(c(7, 9, 8, 6, 10, 12),nrow=2,ncol=3, byrow = TRUE)
[ ,3]
[1, ] 8
[2, ] 12
[1] 8 12
[1] 10 12
[ ,3]
[1, ] 10
[2, ] 12
Q43. What does the function power.anova.test
return?
 the probability of making a Type I error
 the probability of not making a Type II error
 the probability of making a Type II error
 the probability of not making a Type I error
Q44. Review the statement below. What is the effect of covariate:factor
on the analysis?
result < lm(outcome ~ covariate + factor + covariate:factor, data = testcoef)
 It forces the intercepts of the individual regressions to zero.
 It calls for the effect of the covariate within each level of the factor.
 It calls for the effect of each variable from covariate to factor in testcoef.
 It forces the covariate to enter the equation before the factor levels.
Q45. A variable whose type is numeric can contain which items?
 integers and real values
 integers, real, and raw values
 real values only
 integers, real, and logical values
Q46. What is the legitimate name of a data class in R?
 property
 integer
 number
 variant
Q47. How do you extract the values above the main diagonal from a square matrix named Rmat
?

Rmat[upper.tri(Rmat)]

upper.triangular(Rmat)

upper.tri(Rmat)

upper.diag(Rmat)
Q48. x
is a vector of type integer, as shown on line 1 below. What is the type of the result returned by the statement > median(x)?
x < c(12L, 6L, 10L, 8L, 15L, 14L, 19L, 18L, 23L, 59L)
 numeric
 integer
 single
 double
Q49. A list named a
is created using the statement below. Which choice returns TRUE?
a < list("10", TRUE, 5.6)
 is.list(a[1])
 is.numeric(a[1])
 is.logical(a[1])
 is.character(a[1])
Q50. How do you return “October” from x
in this code?
x < as.Date("20181001")
 as.month(x)
 months(x)
 month(x)
 attr(x)
Q51. How do you obtain the row numbers in a data frame named pizza
for which the value of pizza$delivery_min
is greater than or equal to 30?
late_delivery < pizza$delivery_min >= 30
index_late < index(late_delivery)
index_late
late_delivery < pizza$delivery_min >= 30
rownum_late < rownum(late_delivery)
rownum_late
late_delivery < pizza$delivery_min >= 30
which_late < which(late_delivery)
which_late
late_delivery < pizza$delivery_min >= 30
late < pizaa$late_delivery
pizza$late
Q52. Which function returns [1] TRUE FALSE TRUE
?
indat < c("Ash Rd","Ash Cir","Ash St")
 grepl("[RdAveDrSt]", indat)
 grepl(“RdAveDrSt”, indat)
 grepl(“Rd,Ave,Dr,St”, indat)
 grepl("[Rd],[Ave],[Dr],[St]", indat)
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