9.8 Exercise 4. Matrix manipulation

Create the script “exercise4.R” and save it to the “Rcourse/Module1” directory: you will save all the commands of exercise 4 in that script.
Remember you can comment the code using #.

correction

1- Create three numeric vectors x, y, z, each of 4 elements of your choice.

correction

Use rbind() to create a matrix mat (3 rows and 4 columns) out of x, y and z.

correction

2- Create the same matrix now using the matrix function. Repeat the same using the byrow=TRUE parameter: what is different?

correction

3- Add names to mat’s columns: “a”, “b”, “c”, “d”, respectively.

correction

4- Calculate the sum of each row, and the sum of each column

correction

5- Create the matrix mat2 as:

What does function seq() do?

correction

seq generate sequences of numbers. Here, it creates a sequences from 1 to 10 with a step of 2 numbers.

6- What are the dimensions of mat2 (number of rows and number of columns)?

correction

7- Add column names to mat2: “day”, “month” and “year”, respectively.

correction

8- Add row names to mat2: letters “A” to “E”

correction

9- Shows row(s) of mat2 where the month column is greater than or equal to 3.

correction

10- Replace all elements of mat2 that are equal to 2017 with 2018.

correction

11- Multiply all elements of the 2nd column of mat2 by 7. Reassign mat2!

correction

12- Add the column named “time” to mat2, that contains values 8, 12, 11, 10, 8. Save in the new object mat3.

correction

13- Replace all elements of mat3 that are less than 3 with NA.

correction

14- Remove rows from mat3 if a NA is present. Save in the new object mat4.

correction

15- Retrieve the smaller value of each column of mat4.

Try different approaches:

  • Retrieve the minimum for each column one by one.

correction

  • Retrieve the minimum of all columns simultaneously using the apply() function.

correction