adding two series with missing data

Question

I would like to add series a and b together. I know that the keys in series b are always in a, but there will be keys in a that are not in b. I don't want nans to appear in the result.

For example:

In[114] a
Out[114]: 
a    1
b    3
c    2
d    5
dtype: int64

In[115] b
Out[115]: 
b    3
c    2
dtype: int64

If I just use the add function, I will get nans in the missing locations.

In[116] a.add(b)
Out[116]: 
a   NaN
b     6
c     4
d   NaN
dtype: float64

The following is the result I desire:

In[117] c
Out[117]: 
a    1
b    6
c    4
d    5
dtype: int64

Is there a clever way to do this?

Answer 1

use update and nested add, this should give you the desired output. I have tested it in ipython and it works.

d = {'d': 5, 'b': 3, 'c': 2, 'a': 1}

e = {'b': 3, 'c': 2}

Convert to series

ds=pd.Series(d)

es=pd.Series(e)

**ds.update(ds.add(es))**

ds
Out[49]: 
a    1
b    6
c    4
d    5
dtype: int64

Answer 2

>>> a.add(b, fill_value=0)
a    1
b    6
c    4
d    5
dtype: float64