Filling values with unequal indexes

When two Series are added together using the plus operator and one of the index labels does not appear in the other, the resulting value is always missing. Pandas offers the add method, which provides an option to fill the missing value.

Getting ready

In this recipe, we add together multiple Series from the baseball dataset with unequal indexes using the fill_value parameter of the add method to ensure that there are no missing values in the result.

How to do it...

1. Read in the three baseball datasets and set the index as playerID:

>>> baseball_14 = pd.read_csv('data/baseball14.csv',
                              index_col='playerID')
>>> baseball_15 = pd.read_csv('data/baseball15.csv',
                              index_col='playerID')
>>> baseball_16 = pd.read_csv('data/baseball16.csv',
                              index_col='playerID')
>>> baseball_14.head()

2. Use the index method difference to discover which index labels...