Choose several of the ideas listed in Table 3.1 for deriving features from the email and write functions for them. Be sure to check your code against what you expect. Try writing one of these functions in two different ways and compare the output from each. Use exploratory data analysis techniques to check that your code works as expected. Does the output of your function match the values in the corresponding columns of email DF? If not, why do you think this might be the case? Does it appear that this derived variable will be useful in identifying spam or ham?