基于相同的列值合并两个数据框

Question

I want to do vlookup in pandas like in excel. In other words:

• If there are same values in both columns (B and C) then print it in new column D (while keeping column A).
• In any other case put NaN

I did: vlookup = df1.merge(df2, on = 'A') but it copies the column value of B and puts everywhere.

df1 = 

A      B

car    VB
car    K2
car    V9
car    VX

---

df2 = 

A      C

car    VB
car    K2
cat    BN
monkey AS

---

Desired output:

df3 = 
A      D      

car    VB     
car    K2     
cat    NaN
car    NaN    
cat    NaN

---

Answer 1

You should do

df3=df1.merge(df2.rename(columns={'C':'B'}),on=['A','B']).rename(columns={'B':'D'})
     A   D
0  car  VB
1  car  K2