python - 仅当一列满足特定条件时如何合并数据帧

Question

假设我有一个数据框“df_main”:

ID   Type
1    Car
1    Truck
2    Truck

另一个数据框“truck_data”:

Truck_ID         Data
1          TruckData1
2          TruckData2

合并这两个给出数据框:

   ID   Type  Truck_ID        Data
0   1    Car         1  TruckData1
1   1  Truck         1  TruckData1
2   2  Truck         2  TruckData2

当且仅当 Type == 'Truck' 时，如何修改合并语句以仅合并来自 Truck_data 的与 ID 匹配的行？
期望的输出:

   ID   Type  Truck_ID        Data
0   1    Car         1  
1   1  Truck         1  TruckData1
2   2  Truck         2  TruckData2

当前代码:

df_main = pd.DataFrame(columns=['ID', 'Type'], data=[[1, 'Car'], [1, 'Truck'], [2, 'Truck']])
truck_df = pd.DataFrame(columns=['Truck_ID', 'Data'], data=[[1, 'TruckData1'], [2, 'TruckData2']])
df_main = df_main.merge(truck_df, left_on='ID', right_on='Truck_ID', how='left')

Answer 1

Filter the required rows来自 df1/perform merge/concat未过滤的行。

m = df_main.Type.eq('Truck')
merged_df = pd.concat([df_main.loc[~m], df_main.loc[m].merge(truck_df, left_on='ID', right_on='Truck_ID')]

输出:

   ID   Type        Data
0   1    Car         NaN
0   1  Truck  TruckData1
1   2  Truck  TruckData2