As usual, all code below should follow the style guidelines from the lecture slides.
1a. Write a function that returns a Boolean indicating whether the input is numeric or not.
1b. Evaluate your function with input that returns TRUE
1c. Evaluate your function with input that returns FALSE
2a. Write a function returns the absolute value of the input. This function should check to make sure the input is numeric. If the input is not numeric, it should stop with an informative error message.
2b. Evaluate your function with positive numeric input.
2c. Evaluate your function with negative numeric input.
2d. Trigger your custom error message. Note: You will need to add the parameter error = TRUE to your R Markdown code chunk. If you do not, your document will not compile!
3. Write and demonstrate a function that loops through through a numeric input vector and returns a numeric vector of the same length, where the \(i\)th element of the output is equal to the sum of the first \(i\) elements of the input. (Hint: The first element of the output should match the first element of the input. The last element of the output should match the sum of the elements of the input.)
4. Write and demonstrate a function that loops through each element of a matrix and replaces each element with the row index minus the column index. (Hint: use ncol() and nrow())