LinkedIn: R (Programming Language) | Skill Assessment Quiz Solutions | APDaga

▸ R (Programming Language) | LinkedIn Skill Assessment Quiz Solutions

LinkedIn: R (Programming Language) | Skill Assessment Quiz Solutions



  1. 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.


  1. What value does this statement return?
    unclass(as.Date("1971-01-01"))

    • 1
    • 365
    • 4
    • 12


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

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


  1. 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


  1. 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)




  1. 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?
    LinkedIn: R (Programming Language) | Skill Assessment Quiz Solutions


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


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

    • Var_A!
    • \_VarA
    • .2Var_A
    • Var2_A


  1. 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.


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

    • type
    • length
    • attributes
    • scalar


  1. 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?
    LinkedIn: R (Programming Language) | Skill Assessment Quiz Solutions


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




  1. 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)


  1. 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)


  1. 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 ] )


  1. 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


  1. 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”.




  1. 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


  1. 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.


  1. What statement shows the objects on your workspace?

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


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

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


  1. 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




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

    x <- NA
    y <- x/1
    
    • Inf
    • Null
    • NaN
    • NA


  1. 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)


  1. 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),]


  1. 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()


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

    • A

      v1<-list(1,2,3)
      v2<-list(c(4,5,6))
      vbound<-cbind(v1,v2)
      
    • B

      v1<-c(1,2,3)
      v2<-list(4,5,6))
      vbound<-cbind(v1,v2)
      
    • C

      v1<-c(1,2,3)
      v2<-c(4,5,6))
      vbound<-cbind(v1,v2)
      



  1. 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


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

    v <- 1:3
    names(v) <- c("a", "b", "c")
    v[4] <- 4
    
    • ""
    • d
    • NULL
    • NA


  1. 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)]


  1. 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


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