R Language MCQs 2 - R Frequently Asked Questions

1. _________ is function in R to get number of observation in a data frame

ncol( )

nobs( )

n( )

nrow( )

2. If I have two vectors x <- c(1,3, 5) and y <- c(3, 2, 10), what is produced by the expression rbind(x, y)?

A 2 by 2 matrix

A vector of length 3

A vector of length 2

A 2 by 3 matrix

3. Suppose I have a vector x <- c(3, 5, 1, 10, 12, 6) and I want to set all elements of this vector that are less than 6 to be equal to zero. What R code achieves this?

x[x

x[x == 0]

x[x

x[x == 6]

4. Suppose I have a vector x <- 1:4 and y <- 2:3. What is produced by the expression x + y?

A numeric vector with the values 1, 2, 5, 7.

An integer vector with the values 3, 5, 5, 7.

A numeric vector with the values 3, 5, 3, 4.

An error.

5. If I execute the expression x <- 4 in R language, what is the class of the object “x” as determined by the “class()” function?

Real

Numeric

Complex

Integer

6. A key property of vectors in R language is that

Elements of a vector can be of different classes

Elements of a vector can only be a character or numeric

Elements of a vector all must be of the same class

A vector cannot have attributes like dimensions

7. The definition of free software consists of four freedoms (freedoms 0 through 3). Which of the following is NOT one of the freedoms that are part of the definition?

The freedom to sell the software for any price.

The freedom to study how the program works, and adapt it to your needs.

The freedom to run the program, for any purpose.

The freedom to improve the program, and release your improvements to the public, so that the whole community benefits.

8. What function is used to test the missing observation in data frame

is.na( )

na( )

missing( )

NA.miss( )

9. Suppose I have a list defined as x <- list(2, “a”, “b”, TRUE). What does x[[2]] give me?

A list containing the number 2 and the letter “a”.

A character vector with the elements “a” and “b”.

A character vector of length 1.

A list containing a character vector with the elements “a” and “b”.

10. The R language is a dialect of which of the following programming languages?

Matlab and Mathematica

Lisp

SAS

11. What is the class of the object defined by the expression x <- c(4, “a”, TRUE)?

Numeric

Integer

Logical

Character

12. In R language the following are all atomic data types EXCEPT

Character

Data frame

Integer

Logical

R Frequently Asked Questions

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