import pandas as pd import numpy as np books = pd.Series(data = ['Great Expectations', 'Of Mice and Men', 'Romeo and Juliet', 'The Time Machine', 'Alice in Wonderland' ]) authors = pd.Series(data = ['Charles Dickens', 'John Steinbeck', 'William Shakespeare', ' H. G. Wells', 'Lewis Carroll' ]) user_1 = pd.Series(data = [3.2, np.nan ,2.5]) user_2 = pd.Series(data = [5., 1.3, 4.0, 3.8]) user_3 = pd..