Pandas dataframe add 2 dataframes

Question

I need to be able to add the values of two dataframes with the same structure together and form a new dataframe as a result.

eg DF1 + DF2 = DF3

DF1
+------------+----+----+----+
|    date    |  A |  B |  C |
+------------+----+----+----+
| 2017-01-01 | 24 | 15 |  4 |
| 2017-01-02 | 31 | 10 | 12 |
| 2017-01-03 |  9 | 47 |  3 |
+------------+----+----+----+

DF2
+------------+----+----+----+
|    date    |  A |  B |  C |
+------------+----+----+----+
| 2017-01-01 |  4 | 12 | 63 |
| 2017-01-02 | 23 |  0 | 31 |
| 2017-01-03 | 61 | 22 | 90 |
+------------+----+----+----+

DF3
+------------+----+----+----+
|    date    |  A |  B |  C |
+------------+----+----+----+
| 2017-01-01 | 28 | 27 | 67 |
| 2017-01-02 | 64 | 10 | 43 |
| 2017-01-03 | 70 | 69 | 93 |
+------------+----+----+----+

I've been trying to work out how to do this but i'm getting a TypeError

TypeError: unsupported operand type(s) for +: 'datetime.date' and 'datetime.date'

when trying to do:

df3 = df1.add(df2, fill_value=0)

I'm sure i'm missing something simple as it appears to be trying to add the first columns (which is a date and the column I want to match on to add together the values for all other columns) but any help would be greatly appreciated.

Answer 1

You want the date columns to be indices, not normal columns:

df3 = df1.set_index('date').add(df2.set_index('date'), fill_value=0).reset_index()

You use set_index() so that the date columns becomes indices. If you don't want the final dataframe to be date-indexed, you can use reset_index() at the end as @MaxU suggests.