多列 + 条件连接

Question

我想将两个数据框合并在一起（自行车骑行数据框和自行车站数据框）。

我一直在使用 pandas 库，但我似乎无法编写代码来完美地操作连接。最初，我只是加入键“station_id”，但我发现了一个更新的站点数据集，其中包含更多站点，问题是有些站点没有 station_id。对于那些站，我想加入匹配经纬度坐标。

我刚刚使用 station_id 加入数据帧时的初始代码

rides_df = rides_df.rename(columns = {'start_station_id': 'station_id'})
rides_df = rides_df.merge(stations_df[['station_id','station_name']],
                         on = 'station_id', how = 'left')
rides_df = rides_df.rename(columns = {'station_id':'start_station_id',
                                     'station_name':'station_name_start'})

#merge ending station name
rides_df = rides_df.rename(columns = {'end_station_id': 'station_id'})
rides_df = rides_df.merge(stations_df[['station_id', 'station_name']],
                         on = 'station_id', how = 'left')
rides_df = rides_df.rename(columns = {'station_id':'end_station_id',
                                     'station_name': 'station_name_end'})

游乐设施数据帧的结构如下（抽样）：

rides_df = pd.DataFrame([[1912818,'Round Trip',3014,34.0566101,-118.23721,3014,34.0566101,-118.23721],
                 [1933383,'Round Trip',3016,34.0528984,-118.24156,3016,34.0528984,-118.24156],
                  [1944197,'Round Trip',3016,34.0528984,-118.24156,3016,34.0528984,-118.24156],
                  [1940317,'Round Trip','NaN',34.03352,-118.24184,'NaN',34.03352,-118.24184],
                  [1944075,'One Way',3021,34.0456085,-118.23703,3016,34.0566101,-118.23721]]
                 , columns = ['trip_id','trip_route_category','start_station_id','start_lat',
                              'start_lon','end_station_id','end_lat','end_lon'])

车站数据帧的结构如下（抽样）：

stations_df = pd.DataFrame([['Union Station West Portal',34.05661,-118.23721,3014],
                            ['Los Angeles & Temple',34.0529,-118.24156,3016],
                            ['Grand & Olympic',34.04373,-118.26014,3018],
                            ['12th & Hill',34.03861,-118.26086,3019],
                            ['Hill & Washington',34.03105,-118.26709,3020],
                            ['Row DTLA',34.03352,-118.24184,'NaN']], 
                           columns = ['station_name', 'lat', 'lon','station_id'])

我想要的是在游乐设施数据框中添加起始位置和结束位置的车站名称，这样我就有一个“Start_Station_Name”和“End_Station_Name”列。我想加入“station_id”，但如果 station_id 是 NaN，那么开始和结束都匹配 lat&lon。

The data frame that I want as a result is structured as follows:
want_df = pd.DataFrame([[1912818,'Round Trip','Union Station West Portal',3014,34.0566101,-118.23721,'Union Station West Portal',3014,34.0566101,-118.23721],
                 [1933383,'Round Trip','Los Angeles & Temple',3016,34.0528984,-118.24156,'Los Angeles & Temple',3016,34.0528984,-118.24156],
                  [1944197,'Round Trip','Los Angeles & Temple',3016,34.0528984,-118.24156,'Los Angeles & Temple',3016,34.0528984,-118.24156],
                  [1940317,'Round Trip','Row DTLA','Nan',34.03352,-118.24184,'Row DTLA','Nan',34.03352,-118.24184],
                [1944075,'One Way','NaN',3021,34.0456085,-118.23703,'Los Angeles & Temple',3016,34.0566101,-118.23721]]
                 , columns = ['trip_id','trip_route_category','start_station_name','start_station_id','start_lat',
                              'start_lon','end_station_name','end_station_id','end_lat','end_lon'])

Answer 1

这是实现此目的的代码的更新版本：

# rides_df and station_df are slightly modified to make sure that the code works as intended
rides_df = pd.DataFrame([[1912818,'Round Trip',3014,34.0566101,-118.23721,3014,34.0566101,-118.23721],
                 [1933383,'Round Trip',3016,34.0528984,-118.24156,3016,34.0528984,-118.24156],
                  [1944197,'Round Trip',3016,34.0528984,-118.24156,3016,34.0528984,-118.24156],
                  [1940317,'Round Trip','NaN' ,34.03352,-118.24184,3018,34.03352,-118.24184],
                  [1944075,'One Way',3021,34.0456085,-118.23703,3016,34.0566101,-118.23721]]
                 , columns = ['trip_id','trip_route_category','start_station_id','start_lat',
                              'start_lon','end_station_id','end_lat','end_lon'])                          

stations_df = pd.DataFrame([['Union Station West Portal',34.05661,-118.23721,'NaN'],
                            ['Los Angeles & Temple',34.0529,-118.24156,3016],
                            ['Grand & Olympic',34.04373,-118.26014,3018],
                            ['12th & Hill',34.03861,-118.26086,3019],
                            ['Hill & Washington',34.03105,-118.26709,3020],
                            ['Row DTLA',34.03352,-118.24184,'NaN']], 
                           columns = ['station_name', 'lat', 'lon','station_id'])


# Convert to floats to match NaNs
rides_df[["start_station_id", "end_station_id"]] = rides_df[["start_station_id", "end_station_id"]].astype(float)
stations_df["station_id"] = stations_df["station_id"].astype(float)
# Convert the NaNs to another invalid id so they stop matching on merge
stations_df.loc[stations_df["station_id"].isnull(), "station_id"] = -1
# Round so numbers are an exact match
rides_df = rides_df.round(5)

# Merge beginning station name
rides_df = rides_df.rename(columns = {'start_station_id': 'station_id', 
                                      'start_lat': 'lat', 'start_lon': 'lon'})
rides_df = rides_df.merge(stations_df[['station_id','station_name']],
                         on = 'station_id', how = 'left')
# Merge again by looking at lat/lon values
rides_df = rides_df.merge(stations_df[['lat', 'lon','station_name']],
                         on = ['lat', 'lon'], how = 'left')
# Merge the two merge results
rides_df.loc[:, "station_name"] = rides_df["station_name_x"].combine(rides_df["station_name_y"], lambda x,y: x if not x!=x else y)
rides_df.drop(["station_name_x", "station_name_y"], axis=1, inplace=True)
rides_df = rides_df.rename(columns = {'station_id':'start_station_id',
                                     'station_name':'start_station_name', 
                                     'lat':'start_lat', 'lon':'start_lon'})

# Merge ending station name
rides_df = rides_df.rename(columns = {'end_station_id': 'station_id',
                                      'start_lat': 'lat', 'start_lon': 'lon'})
rides_df = rides_df.merge(stations_df[['station_id', 'station_name']],
                         on = 'station_id', how = 'left')
rides_df = rides_df.merge(stations_df[['lat', 'lon','station_name']],
                         on = ['lat', 'lon'], how = 'left')
rides_df.loc[:, "station_name"] = rides_df["station_name_x"].combine(rides_df["station_name_y"], lambda x,y: x if not x!=x else y)
rides_df.drop(["station_name_x", "station_name_y"], axis=1, inplace=True)
rides_df = rides_df.rename(columns = {'station_id':'end_station_id',
                                     'station_name': 'end_station_name',
                                     'lat':'start_lat', 'lon':'start_lon'})

print(rides_df)

输出：

   trip_id trip_route_category  start_station_id  start_lat  start_lon  end_station_id   end_lat    end_lon         start_station_name           end_station_name
0  1912818          Round Trip            3014.0   34.05661 -118.23721          3014.0  34.05661 -118.23721  Union Station West Portal  Union Station West Portal
1  1933383          Round Trip            3016.0   34.05290 -118.24156          3016.0  34.05290 -118.24156       Los Angeles & Temple       Los Angeles & Temple
2  1944197          Round Trip            3016.0   34.05290 -118.24156          3016.0  34.05290 -118.24156       Los Angeles & Temple       Los Angeles & Temple
3  1940317          Round Trip               NaN   34.03352 -118.24184          3018.0  34.03352 -118.24184                   Row DTLA            Grand & Olympic
4  1944075             One Way            3021.0   34.04561 -118.23703          3016.0  34.05661 -118.23721                        NaN       Los Angeles & Temple