EXERCISES

1. The expression 2**4 returns [ ]

(a) 2   (b) 24   (c) 16   (d) 32

2. We want to select two columns from a data frame called Clients, which expression is correct [ ]

(a) Clients[(1,2)] (b) Clients[c(1,2)] (c) Clients[,c(1,2)] (d) Clients[c(1,2),]

3. What is the value of the expression 2+NA [ ]

(a) NA   (b) NULL   (c) 2   (d) 0

4. Which of the following is default prompt for Ubuntu environment [ ]

(a) <   (b) >   (c) >>   (d) *

5. Which of the following is invalid assignment ? [ ]

(a) m <- matrix(nrow = 2, ncol = 3) (b) m <- matrix(nrow = 2, ncol = 3.5)

(c) None of the above   (d) All of the above

6. Which of the following extracts first element from the following vector ?

> x <- c("a", "b", "c", "c", "d", "a") [ ]

(a) x[10]   (b) x[1]   (c) x[0]   (d) None of the mentioned

7. Which of the following extracts first four element from the following vector ?

> x <- c("a", "b", "c", "c", "d", "a") [ ]

a) x[0:4]   b) x[1:4]   c) x[0:3]   d) All of the mentioned

8. What would be the output of the following code > x <- c("a", "b", "c", "c", "d", "a")

x[c(1, 3, 4)] [ ]

(a) “a” “b” “c”   b) “a” “c” “c”   c) “a” “c” “b”   d) All of the mentioned

9. Which of the following would print the following output ? [ ]

foo   bar

1   TRUE

2   TRUE

3   FALSE

4   FALSE

a)> x <- data.frame(foo = 1:4, bar = c(F, T, F, F))

> x

b)> x <- data.frame(foo = 1:6, bar = c(F, T, F, F))

> x

c)> x <- data.frame(foo = 1:4, bar = c(T, T, F, F))

> x

d) All of the Above

10. Consider the following data frame “df”

    x     y     z

1   1    6    aa

2   5    9    aa

3   7    3    bb

4   9    7    bb

5   2   12   cc

I we execute the following command in R, mydf<=df[df$x<=7, ]

a) copy of df b) all rows with x column <=7 are dropped

c) all rows with x column <=7 are selected d) vector of number <=7

II FIIL IN THE BLANKS

11. The default data structure in R _________________________

12. The row names can be assigned to the data frame using ________________ function.

13. The function used for checking the current working directory of R is __________.

14. Let x<-c(4,”a”,TRUE)

then class(x)=_____________

15. Write the R statement to create a vector of odd numbers between 10 to _______________________

16. What would be the output of the following code ?

> x <- matrix(1:6, 2, 3)

>x[1,2]=________________________

17. What would the following code print ?

> x <- data.frame(foo = 1:4, bar = c(T, T, F, F))

> ncol(x) _______________________

18. x<-c(4,”a”,TRUE) then class(x) is _____________

19. Write the statement to display the output

1 2 3 1 2 3 ________________

20. __________ function is used for displaying the current working directory in R.