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

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