In pandas, :meth:`Series.isna` and :meth:`Series.notna` can be used to filter the rows.
.. ipython:: python outer_join[outer_join["value_x"].isna()] outer_join[outer_join["value_x"].notna()]
pandas provides :ref:`a variety of methods to work with missing data <missing_data>`. Here are some examples:
.. ipython:: python outer_join.dropna()
.. ipython:: python outer_join.ffill()
Using the mean:
.. ipython:: python outer_join["value_x"].fillna(outer_join["value_x"].mean())