linkedin-skill-assessments-quizzes

R (Programming Language)

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

Q2. What value does this statement return?

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

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

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

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

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

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

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

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

Q9. Which is not a property of lists and vectors?

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?

Image

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

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?

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"

Q14. What does c contain?

a <- c(3,3,6.5,8)
b <- c(7,2,5.5,10)
c <- a < b

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)

Q16. What is mydf$y in this code?

mydf <- data.frame(x=1:3, y=c("a","b","c"), stringAsFactors=FALSE)

Q17. How does a vector differ from a list?

Q18. What statement shows the objects on your workspace?

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

Q20. Review line 1 below. What does the statement in line 2 return?

1 mylist <- list(1,2,"C",4,5)
2 unlist(mylist)

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

x <- NA
y <- x/1

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?

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)

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

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)

Q27. What is the value of names(v[4])?

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

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

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

image

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

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

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

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

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"

Q33. What does R return?

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

Q34. What does the expression mtrx * mtrx do ?

> mtrx <- matrix( c(3,5,8,4), nrow= 2,ncol=2,byrow=TRUE)
> newmat <- mtrx * mtrx
> newmat
     [,1] [,2]
[1,]    9   25
[2,]   64   16

# The `%*%` operator gives matrix multiplication
> mtrx %*% mtrx
     [,1] [,2]
[1,]   49   35
[2,]   56   56

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

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

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

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?

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

Q39. StDf is a data frame. Based on this knowledge, what does this statement return?

StDf[, -1]

Q40. Which statement enables you to interactively open a single file?

Q41. How are these data types alike: logical, integer, numeric, and character?

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?

Q44. Review the statement below. What is the effect of covariate:factor on the analysis?

result <- lm(outcome ~ covariate + factor + covariate:factor, data = testcoef)
# Example call to demonstrate.  `Species` is a Factor.  Petal.Length, Petal.Width are numeric.
# see `help(formula)` for more details on the formula specification.  `:` is "effect modification" or "interaction"

> summary(lm(Petal.Length ~ Petal.Width + Species + Petal.Width:Species, data = iris))
...
Petal.Width:Speciesversicolor   1.3228     0.5552   2.382   0.0185 *
Petal.Width:Speciesvirginica    0.1008     0.5248   0.192   0.8480
...

Q45. A variable whose type is numeric can contain which items?

Q46. What is the legitimate name of a data class in R?

Q47. How do you extract the values above the main diagonal from a square matrix named 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)

Q49. A list named a is created using the statement below. Which choice returns TRUE?

a <- list("10", TRUE, 5.6)

Q50. How do you return “October” from x in this code?

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

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")