CODEWITHSUNDEEP
pythonpandasdataframejoinmerge
P.J
P.J

Reputation: 197

Join two dataframes along columns with non-unique index

I have two data frames that I want to join them along columns. The index is not unique:

df1 = pd.DataFrame({'A': ['0', '1', '2', '2'],'B': ['B0', 'B1', 'B2', 'B3'],'C': ['C0', 'C1', 'C2', 'C3']}):
    A   B   C
0  0  B0  C0
1  1  B1  C1
2  2  B2  C2
3  2  B3  C3

df2 = pd.DataFrame({'A': ['0', '2', '3'],'E': ['E0', 'E1', 'E2']},index=[0, 2, 3])
    A   E
0  0  E0
1  2  E1
2  3  E2

A should be my index. what I want is:

    A   B   C   E
0  0  B0  C0    E0
1  1  B1  C1    NAN
2  2  B2  C2    E1
3  2  B3  C3    E1

This pd.concat([df1, df2], 1) gives me error: 

Reindexing only valid with uniquely valued Index objects

Upvotes: 1

Views: 4715

Answers (2)

cs95
cs95

Reputation: 402263

Maybe you're looking for a left outer merge.

df1.merge(df2, how='left')
   A   B   C    E
0  0  B0  C0   E0
1  1  B1  C1  NaN
2  2  B2  C2   E1
3  2  B3  C3   E1

Upvotes: 4

BENY
BENY

Reputation: 323226

By using combine_first

df1.combine_first(df2).dropna(subset=['A'],axis=0)
Out[320]: 
    A   B   C    D    E
0  A0  B0  C0   D0   E0
1  A1  B1  C1  NaN  NaN
2  A2  B2  C2   D1   E1
2  A3  B3  C3   D1   E1

After you edit:

By using combine_first

df1.combine_first(df2.set_index('A'))
Out[338]: 
   A   B   C    E
0  0  B0  C0   E0
1  1  B1  C1  NaN
2  2  B2  C2   E1
3  2  B3  C3   E2

Or 

pd.concat([df1,df2.set_index('A')],axis=1)
Out[339]: 
   A   B   C    E
0  0  B0  C0   E0
1  1  B1  C1  NaN
2  2  B2  C2   E1
3  2  B3  C3   E2

Upvotes: 2

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