Here, We see **R (Programming Language) LinkedIn Skill Assessment Answer**. This assessment test consists 15-20 MCQs to demonstrate your knowledge in your selected skills. MCQs comes from different topics – R Data Structures, Data Management, Functions, Operators, Statistics.

## R (Programming Language) Documentation ->

**R (Programming Language) LinkedIn Skill Assessment** :-

**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()

## Q**4. 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?

`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 names 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 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$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 * 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 ?

**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?

**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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