Pandas merge using dfA column == dfB index [duplic

问题:

This question already has answers here:

Pandas Merging 101 (3 answers)

Closed 2 years ago.

How to merge (left join) using column value from dataframe A and index of dataframe B?

For example:

>>> A              >>> B
    lkey value         rkey value
0   foo  1         0   foo  5
1   bar  2         1   bar  6
2   baz  3         2   qux  7
3   foo  4         3   bar  8

to get:

   lkey  value_x  rkey  value_y
 0 foo   1        bar   6
 1 bar   2        qux   7
 2 baz   3        bar   8
 3 foo   4        NaN   NaN

回答1:

try using left_on and right_index to do the merging, like:

m = pd.merge(dfA, dfB, right_index = True, left_on='value')