R MCQs
R MCQs
These R multiple-choice questions and their answers will help you strengthen your grip on the subject of R. You can prepare for an upcoming exam or job interview with these 100+ R MCQs.
So scroll down and start answering.
1: Which R function fits a simple linear regression model of x predicting y?
A. lm(x ~ y)
B. proc reg; model y=x; run;
C. lm(y ~ x)
D. regress y x
2: Suppose you need to randomly assign 100 study subjects into one of 5 groups such that there are exactly 20 subjects in each group. Which of the following R functions creates a variable Y that randomly distributes the 100 study subjects into 5 groups of equal size?
A. ytemp <- rnorm(100, 0, 1); Y <- cut(ytemp, breaks=c(-10, -2, -1, 1, 2, 10))
B. Y <- rbinom(100, 5, 0.5)
C. Y <- sample(rep(c(1:5), each=20), size=100)
D. Y <- sample(c(1, 2, 3, 4, 5), 100, replace = TRUE)
3: What is an appropriate syntax for a 'for' loop in R to run specific simulation code nnn times?
A. for(i in 1:nnn) { <simulation code> }
B. for i in 1:nnn: <simulation code>
C. for(i - nnn) { <simulation code> }
D. for(i=1, nnn, 1) { <simulation code> }
4: What does 'x:y' mean in R?
A. It means a range from x to y.
B. It means that x and y are correlated.
C. It means that y logically follows from x.
D. It means that x and y are real numbers.
E. It means odds of x to y apply to this operation.
5: What does the following R code output? seq(2,10, by=2)
A. 2 10
B. 1 3 5 7 9
C. 2 4 6 8 10
D. 2
6: Given the command: Z <- array(h, dim=c(3,4,2)), dim(Z) stands for:
A. the data vector as it was in h
B. the entire array as an array
C. the array of all zeros
D. the dimension vector c(3,4,2)
7: What's the output for command: print("Hello World")
A. [1] 2
B. [1] "Hello World"
C. NULL
D. NA
E. [1] Hello World
8: What is the current proper style for assigning the numeric value 1 to a variable called "a"?
A. a = 1
B. a == 1
C. a <<- 1
D. a <- 1
E. a -> 1
9: What is the value of x after executing the command: x <- 3 < 4
A. 4
B. 3
C. TRUE
D. FALSE
E. 1
10: Which R function imports a comma separated file "X.csv"?
A. import.csv("X.csv")
B. import("X.csv")
C. read.csv("X.csv")
D. read("X.csv")
11: Which R code will sort the vector X <- c(1,5,3,9,7) from largest to smallest?
A. sort(X, decreasing=T)
B. sort(X)
C. order(X)
D. X[sort(X)]
12: Which R function provides basic descriptive summary statistics for a numeric vector x?
A. summarize x
B. summary(x)
C. proc contents x;
D. summarize(x)
13: Which R function provides a histogram of the numeric vector X?
A. plot(X)
B. hist(X)
C. plot X
D. plot.hist(X)
14: How does one obtain the FIRST element of x when x <- 1:9?
A. x$1
B. x[0]
C. x.1
D. x[1]
E. x$0
15: What does the following R function output? abs(10 - 3 * 4)
A. 0
B. -2
C. NA
D. 2
16: The entities on which R operates are technically known as:
A. objects
B. mode
C. events
D. commands
17: Which of the following is NOT a valid data import function?
A. readdata
B. scan
C. read.csv
D. read.table
18: Which command is used to test if an object is a time series?
A. as.ts
B. is.ts
C. ts
D. if.ts
19: In order to apply lag operator for the data, you should:
A. convert the data into integer
B. convert the data into vector
C. convert the data into matrices
D. convert the data into the time-series object
20: What is the default value for missing data that is read into R via read.table or read.csv?
A. NA
B. NaN
C. #VALUE!
D. [a blank cell]
E. NULL
21: What does the option 'cex' do in the following R function? text(0, 1, "Hello", cex=2)
A. Surpresses printing of the word "Hello"
B. Right justifies the word "Hello"
C. Prints the word "Hello" in bold font
D. Increases the size of the word "Hello" by a factor of 2
22: In the plot( ) function, what option is used to specify that the x-axis displays values from 0 to 1?
A. xlim=c(0, 1)
B. xlimit="0, 1"
C. xlim="0, 1"
D. xlab=c(0, 1)
23: What is the output of the following R code? x<-2; y <- c(1:3); paste("The value of x is", x, "and the value of y[x] is", y[x], sep=" ")
A. "The value of x is 2 and the value of y[x] is c(1:3)[2]"
B. "The value of x is 2 and the value of y[x] is 4"
C. "The value of x is 2 and the value of y[x] is 2"
D. "The value of x is 2 and the value of y[x] is 6"
24: What's the output for command: seq(from = 1, to = 5, by = 3)
A. 1 4
B. 1 4 7
C. 1 3 5
D. 1 2 3 4 5
25: Which R function adds a line with slope 1 and intercept 0 into an existing plot of Y versus X?
A. lines(0, 1)
B. lty=c(0, 1)
C. abline(0, 1)
D. smooth.spline(0, 1)
26: What is the output of this command: > is.na( c( 1:3, NA ) )
A. [1] FALSE FALSE FALSE TRUE
B. [1] FALSE
C. Throws an error.
D. [1] TRUE
E. [1] NA NA NA TRUE
27: Suppose we define X <- NA. What is the output for > is.nan( X ); is.na( X )
A. [1] TRUE [1] FALSE
B. [1] TRUE [1] TRUE
C. [1] FALSE [1] TRUE
D. NULL
E. [1] NaN [1] NA
28: What is the value of Y? X <- c(1,2,2,2,3,3,4,4,5,6); Y <- unique(X[which(X<4)])
A. 3
B. 1 2 3 4
C. 1 2 2 2 3 3
D. 1 2 3
29: Which function is used to load a CSV file into R?
A. read.table()
B. load.table()
C. load()
D. read()
30: What R function can be used to tabulate values of categorical variable Y (columns) by categorical variable X (rows)?
A. tabulate(X, Y)
B. table(Y ~ X)
C. table(X*Y)
D. table(X, Y)
31: What is the output for the command: is.na(0/0)?
A. NA
B. TRUE
C. FALSE
D. -Inf
32: What does the following R code output? Y <- c(1,2,3); X <- rep(c(1,length(Y)), times=2); X
A. 1 2 1 2
B. 1 1
C. 1 1 3 3
D. 1 3 1 3
33: What is the output of the following R function? yyy <- c(1, 3, NA); fff <- function(xxx) {mean(xxx)}; fff(yyy)
A. NULL
B. 2
C. 1.5
D. NA
34: What is the output of dim(matrix(1:10, ncol=2))?
A. 5 2
B. 10
C. 2 5
D. 20
35: In a linear regression model with outcome y and linear predictors x1, x2, and x3, which R code correctly includes an interaction term between x1 and x2?
A. lm(y ~ x1:x3 + x1:x2)
B. lm(y ~ x1 + x2 + x3 + x1*x2)
C. lm(y ~ x1 + x2 + x3 + interaction(x1, x2))
D. lm(y ~ x1:x2 + x3)
36: Which of the following is NOT included in CRAN's R distribution?
A. Time Series Analysis
B. Generalized Linear Models
C. Linear Mixed Effects Models
D. Analysis of Variance Models
E. Clustering Tools
37: In order to assess whether x and y are equal, you can use the command:
A. x == y
B. x != y
C. x =! y
D. x =~ y
E. x %% y
38: Which R function will generate a mean for each row in a numeric matrix X with intermittent missing values?
A. mean(X[1:length(X[,1]),], na.rm=T)
B. apply(X, 1, mean, na.rm=T)
C. by(X, 1, mean, na.rm=T)
D. apply(X, 1, mean)
39: Suppose numeric vectors X, Y, and Z are all of the same length. Which R command will create a matrix with rows X, Y, Z?
A. matrix(X, Y, Z, nrow=3)
B. matrix(cbind(X, Y, Z), nrow=3)
C. matrix(rbind(X, Y, Z), nrow=3)
D. matrix(rbind(X, Y, Z), ncol=3)
40: Which R command is used to merge two data sets X and Y by the variable "ID" that includes all records from both data sets?
A. merge( X, Y, by = "ID")
B. merge( X, Y, by = "ID", all = TRUE )
C. merge( X, Y, sort = "ID", all = TRUE)
D. combine( X, Y, by = "ID")
41: Which object class can contain multiple unrelated object classes of potentially different sizes?
A. matrix
B. vector
C. data.frame
D. list
E. array
42: I want to use the sort() function, and I see in the help file that I my sort "an R object with a class, or a numeric, complex, character, or logical vector." Given this guidance, which is a valid call to sort()?
A. sort( data.frame( x = c(10, -3, 4) ) )
B. sort( list( 10, -3, 4) )
C. sort( c( 10, -3, 4) )
D. sort( 10, -3, 4 )
43: Which is NOT a valid R function for obtaining the residuals from a simple linear regression model of X predicting Y?
A. lm(Y ~ X)$residuals
B. lm(Y ~ X)$residuals - lm(Y ~ X)$fitted.values
C. residuals(lm(Y ~ X))
D. Y - lm(Y - X)$fitted.values
44: Let X be a 3x4 matrix with non-zero values. The result of: > apply(X, 2, mean), is:
A. equal to the result of: >c(mean(X[,1]), mean(X[,2]), mean(X[,3]))
B. equal to the result of: >c(mean(X[1,]), mean(X[2,]), mean(X[3,]), mean(X[4,]))
C. equal to the result of: >c(mean(X[,1]), mean(X[,2]), mean(X[,3]), mean(X[,4]))
D. equal to the result of: >c(mean(X[1,]), mean(X[2,]), mean(X[3,]))
45: Suppose X is the vector c(1:10). Which R code will swap the values of the 3rd element of X and the 7th element of X?
A. X[c(3,7)] <- X[c(7,3)]
B. replace(X, c(3, 7), c(7,3)
C. X[7] <- X[3]; X[3] <- X[7]
D. X[3] <- X[7]; X[7] <- X[3]
46: What is the output for the command: > is.na( NaN ) ?
A. [1] NULL
B. [1] TRUE
C. [1] -Inf
D. [1] NaN
E. [1] FALSE
47: What does the following R function output? xxx <- c(1, 1, 2, 2, 3, 3, NA, NA); yyy <- c(rep(0, 4), rep(1, 4)); cor(yyy, xxx)
A. An error message
B. NA
C. A correlation coefficient
D. R squared
48: Which R function can be used to produce a simple scatterplot of a numeric vector Y versus a numeric vector X?
A. scatter( X ~ Y )
B. plot( data.frame( Y ~ X ) )
C. plot( X ~ Y )
D. xyplot( X, Y )
49: What is the value of Y? Y <- 10 + 100 & !is.na(0)
A. True
B. 0
C. False
D. 110
50: Given the command: Z <- array(h, dim=c(3,4,2)), Z[] with an empty subscript or Z with no subscript stands for:
A. the dimension vector c(3,4,2)
B. the entire array as an array
C. the array of all zeros
D. the data vector as it was in h
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