Pandas join/merge/concat two dataframes

Question

I am having issues with joins in pandas and I am trying to figure out what is wrong. Say I have a dataframe x:

Answer 1

Does your index have duplicates x.index.is_unique? If so would explain the behavior you're seeing:

In [16]: left
Out[16]: 
            a
2000-01-01  1
2000-01-01  1
2000-01-01  1
2000-01-02  2
2000-01-02  2
2000-01-02  2

In [17]: right
Out[17]: 
            b
2000-01-01  3
2000-01-01  3
2000-01-01  3
2000-01-02  4
2000-01-02  4
2000-01-02  4

In [18]: left.join(right)
Out[18]: 
            a  b
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-01  1  3
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4
2000-01-02  2  4