Exercises

1. In R we have vectors and matrices. You can create your own vectors with the function c.

    c(1,5,3,4)
   

   They are also the output of many functions such as:

    rnorm(10)
   

   You can turn vectors into matrices using functions such as rbind, cbind or matrix.

   Create the matrix from the vector 1:1000 like this:

    X = matrix(1:1000,100,10)
   

   What is the entry in row 25, column 3?

2. Using the function cbind, create a 10 x 5 matrix with first column x=1:10. Then add 2*x, 3*x, 4*x and 5*x to columns 2 through 5. What is the sum of the elements of the 7th row?

3. Which of the following creates a matrix with multiples of 3 in the third column?

   • A) matrix(1:60,20,3)
   • B) matrix(1:60,20,3,byrow=TRUE)
   • C) x=11:20; rbind(x,2*x,3*x)
   • D) x=1:40; matrix(3*x,20,2)