pandas: merging dataframes and replacing values

Question

I have two dataframes:

   A = pd.DataFrame(data=np.array([['t1',1,'t2',2]]).reshape(2,2),columns=['a','b'])

A
Out[6]: 
    a  b
0  t1  1
1  t2  2

B = pd.DataFrame(data=np.array([[1,2,3],[2,5,6],[3,6,7]]).reshape(3,3),columns=['x','y','z'])

B
Out[8]: 
   x  y  z
0  1  2  3
1  2  5  6
2  3  6  7

I am trying to basically match columns 'x' of dataframe B on column 'b' dataframe A but replace the matched values with column 'a' of dataframe A.

ie I want to merge the two dataframes so that the output will look like this:

   x   y  z
0  t1  2  3
1  t2  5  6
2  3   6  7

Any ideas how to go about this?

Answer 1

B.loc[B.x.astype(str).isin(A.b), 'x'] = A.a

B

    x  y  z
0  t1  2  3
1  t2  5  6
2   3  6  7