Multiple Choices: Matrices

Questions

1. What function is used to create a matrix in R?

cbind() rbind() matrix() data.frame()

2. What is the output of matrix(1:6, nrow = 2, ncol = 3)?

A matrix with 3 rows and 2 columns A matrix with 2 rows and 3 columns, filled column-wise A matrix with 2 rows and 3 columns, filled row-wise An error

3. Which function can bind matrices or vectors as columns to create a new matrix?

rbind() bind() cbind() add()

4. If mat <- matrix(1:9, nrow = 3), what does mat[2, 3] return?

2 3 5 6

5. What will dim(matrix(1:4, nrow = 2, ncol = 2)) return?

c(2, 4) c(4, 1) c(2, 2) 2

6. Which function would you use to get the transpose of a matrix in R?

invert() flip() transpose() t()

7. If mat <- matrix(1:4, nrow = 2), what will mat %*% mat return?

Element-wise product of mat The matrix multiplication of mat by itself The sum of mat elements An error

8. What is the result of ncol(matrix(1:6, nrow = 2))?

2 3 6 1

9. Which of the following will convert a matrix to a vector?

c() as.vector() flatten() reduce()

10. What does diag(matrix(1:9, nrow = 3)) return?

c(1, 5, 9) c(3, 5, 7) A matrix with only the diagonal elements c(1, 2, 3)

11. If m <- matrix(1:12, nrow = 3, byrow = TRUE), what will m[2, ] return?

The second column of m The second row of m c(4, 5, 6) An error

12. What function would you use to get the inverse of a matrix in R?

inverse() inv() solve() t()

13. If mat <- matrix(c(2, 4, 3, 8), nrow = 2), what is the output of apply(mat, 1, sum)?

c(5, 11) c(6, 12) c(10, 15) c(2, 4, 3, 8)

14. What will nrow(matrix(1:10, nrow = 5)) return?

10 5 2 1

15. Which of the following functions will extract the diagonal elements of a matrix?

diag() diag_extract() trace() diag_only()

16. If A is a matrix, what does t(A) %*% A represent?

The transpose of A The element-wise product of A The matrix multiplication of A transpose with A The inverse of A

17. If mat <- matrix(1:9, nrow = 3), what does mat[ , c(1, 3)] return?

The entire matrix The first and third rows The first and third columns An error

18. Which function reshapes a matrix into a vector by filling it column-wise?

vectorize() flatten() c() as.vector()

19. If A <- matrix(1:4, nrow = 2) and B <- matrix(4:1, nrow = 2), what does A * B do?

Element-wise multiplication Matrix multiplication Division An error

20. If mat <- matrix(1:6, nrow = 2), what does colSums(mat) return?

The sum of each row The sum of each column The total sum of all elements The diagonal elements

21. If m <- matrix(1:9, nrow = 3), what is the output of m[ , -2]?

The second column The first and third columns The matrix without the second row An error

22. What will rowMeans(matrix(1:6, nrow = 2)) return?

The mean of each row The mean of each column The sum of each row An error

23. If A <- matrix(1:4, nrow = 2), which command returns the determinant of A?

determinant(A) det(A) solve(A) diag(A)

24. What will dim(matrix(1:12, ncol = 4)) return?

c(12, 1) c(3, 4) c(4, 3) An error

25. If mat <- matrix(1:12, nrow = 3), what does mat[mat > 5] return?

The entire matrix A vector of elements greater than 5 The indices of elements greater than 5 An error

26. Which function extracts only the lower triangular part of a matrix in R?

lower.tri() diag() low.matrix() bottom()

27. If mat <- matrix(1:9, nrow = 3), what does sum(mat) return?

9 The sum of each row The sum of all elements in mat The sum of each column

28. What does is.matrix(c(1, 2, 3)) return?

TRUE FALSE NULL An error

29. If A <- matrix(c(1, 2, 3, 4), nrow = 2), which of the following commands will return TRUE if A is a square matrix?

is.square(A) nrow(A) == ncol(A) square(A) dim(A)

30. If A <- matrix(1:9, nrow = 3), what does A[ , 3] return?

The third row as a matrix The third column as a vector The entire matrix An error