熊猫-在数据框之间查找值，并为匹配项添加一系列值

Question

I am trying to search for the values of DataframeB.ColA in DataframeA.IDCol2 and then create a dataframe with the DataframeA.IDCol1 and the sum of DataframeA.IDCol3 for the values that were matched.

DataframeA

        IDCol1      IDCol2      IDCol3
0       ABC         123         2
1       ABC         456         5
2       ABC         789         2
3       ABC         1011        1
4       CDE         123         3
5       CDE         456         2
6       CDE         CCC         4
7       CDE         AAA         1

DataframeB

        ColA        
0       123     
1       456     
2       CCC     
3       1011      

Output

        Col     Sum     
0       ABC     8       
1       CDE     9    

Answer 1

Use DataFrame.merge first and then aggregate sum :

df = (DataframeA.merge(DataframeB, left_on='IDCol2', right_on='ColA')
                .groupby('IDCol1', as_index=False)['IDCol3']
                .sum())
print (df)
  IDCol1  IDCol3
0    ABC       8
1    CDE       9

Another solution:

s = DataframeB['ColA']
df = DataframeA.set_index('IDCol1').query('IDCol2 in @s')['IDCol3'].sum(level=0).reset_index()
print (df)
  IDCol1  IDCol3
0    ABC       8
1    CDE       9

Answer 2

You can merge , groupby IDCol1 and aggregate with the sum :

(DataframeA.merge(DataframeB, left_on='IDCol2', right_on='ColA')
           .groupby('IDCol1')
           .IDCol3.sum()
           .reset_index())

   IDCol1  IDCol3
0    ABC       8
1    CDE       9

Answer 3

Use series.isin() and groupby() with sum :

dfA[dfA.IDCol2.isin(dfB.ColA)].groupby('IDCol1')['IDCol3'].sum().reset_index(name='Sum')

---

  IDCol1  Sum
0    ABC    8
1    CDE    9