How to concatenate dataframe and series with different index

Question

if I have one dataframe and series like these

  bi            sm
0  A          0  a
1  B          1  b
2  C          2  C

I can concatenate like this

dfA['sm'] = dfB

  big  sm
0 A    a
1 B    b 
2 C    c

However I have one dataframe and seriese, each has the different index but same row numbers.

            bi            sm
2017-11-04  A          0  a
2017-11-03  B          1  b
2017-11-02  C          2  C 

I would like to concatenate these two into this

            bi  sm
2017-11-04  A   a
2017-11-03  B   b
2017-11-02  C   C 

How can I make it???

Answer 1

Make both dataframes have the same index, then concatenate:

pd.concat([dfA, dfB.set_index(dfA.index)], axis=1)
#           bi sm
#2017-11-04  A  a
#2017-11-03  B  b
#2017-11-02  C  c

Answer 2

You can assign dfB.sm as values values

Option 1

In [209]: dfA['sm'] = dfB.sm.values

In [210]: dfA
Out[210]:
           bi sm
2017-11-04  A  a
2017-11-03  B  b
2017-11-02  C  C

Option 2

In [215]: dfA.assign(smm=dfB.sm.values)
Out[215]:
           bi smm
2017-11-04  A   a
2017-11-03  B   b
2017-11-02  C   C

Note: dfA, dfB are both dataframes.