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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("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?

Image

  • 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?

Image

  • 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 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?

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
  • 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("2018-10-01")
  • 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")
StopDate-StartDate
  • "1970-01-02"
  • time difference of one day
  • time difference of two days
  • 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
  • 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 differents 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. Which strings could be returned by the function ls(path = "^V")?

  • ANOVAData, anovadata
  • VisitPCA, VarX
  • VisitPCA, varx
  • Xvar, Yvar