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 has the .add method, which provides an option to fill the missing value. Note that these Series do not include duplicate entries, hence there is no need to worry about a Cartesian product exploding the number of entries.

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

How to do it…

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

   >>> baseball_14 = pd.read_csv(
   ...     "data/baseball14.csv", index_col="playerID"
   ... )
   >>> baseball_15 = pd.read_csv(
   ...     "data/baseball15.csv", index_col="playerID"
   ... )
   >>...