pandas.Dataframe: filling missing values from another DF

Question

For example I have this:

df_1 = pd.DataFrame({'A': [3 for _ in xrange(10)],
                     'B': [3 for _ in xrange(10)],
                     'C': [3 for _ in xrange(10)]})
df_2 = pd.DataFrame({'A': [2 for _ in xrange(5)],
                     'B': [2 for _ in xrange(5)],
                     'C': [2 for _ in xrange(5)]})

print(df_1 - df_2)

and output will be as expected:

    A   B   C
0   1   1   1
1   1   1   1
2   1   1   1
3   1   1   1
4   1   1   1
5 NaN NaN NaN
6 NaN NaN NaN
7 NaN NaN NaN
8 NaN NaN NaN
9 NaN NaN NaN

How can I fill missing values in newly created DF with values from df_1?

Matthieu · Accepted Answer · 2013-03-17 23:56:05Z

4

You can use combine_first to fill in the missing values:

In [2]: (df_1 - df_2).combine_first(df_1)
Out[2]:
   A  B  C
0  1  1  1
1  1  1  1
2  1  1  1
3  1  1  1
4  1  1  1
5  3  3  3
6  3  3  3
7  3  3  3
8  3  3  3
9  3  3  3

answered Mar 17, 2013 at 23:56

Matthieu

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