如何使用pandas进行左连接

我有2个数据框，它看起来像这样：DF1：

Product, Region, ProductScore
AAA, R1,100
AAA, R2,100
BBB, R2,200
BBB, R3,200

DF2：

Region, RegionScore
R1,1
R2,2

我如何让这2个加入1个数据帧，结果如下：

Product, Region, ProductScore, RegionScore
AAA, R1,100,1
AAA, R2,100,2
BBB, R2,200,2

非常感谢！

EDIT1：

我使用了df.merge（df_new）得到了这个错误消息：

File "C:\Python34\lib\site-packages\pandas\core\frame.py", line 4071, in merge
    suffixes=suffixes, copy=copy)
  File "C:\Python34\lib\site-packages\pandas\tools\merge.py", line 37, in merge
    copy=copy)
  File "C:\Python34\lib\site-packages\pandas\tools\merge.py", line 183, in __init__
    self.join_names) = self._get_merge_keys()
  File "C:\Python34\lib\site-packages\pandas\tools\merge.py", line 318, in _get_merge_keys
    self._validate_specification()
  File "C:\Python34\lib\site-packages\pandas\tools\merge.py", line 409, in _validate_specification
    if not self.right.columns.is_unique:
AttributeError: 'list' object has no attribute 'is_unique'

EDIT2：我意识到我的df_new是一个数据系列（使用groupby创建）而不是数据帧 . 现在我已将其转换为数据框，这里是info：print（df.info（））Int64Index：1111条目，0到1110数据列（共8列）：product 1111非null对象reviewuserId 1111非null object reviewprofileName 1111非null对象reviewelpfulness 881非null float64 reviewcore 1111非null float64 reviewtime 1111非null int64 reviewummary 1111非null对象reviewtext 1111非null对象dtypes：float64（2），int64（1），object （5）内存使用量：56.4 KB无

print(df_new_2.info())

<class 'pandas.core.frame.DataFrame'>
Index: 1089 entries, A100Y8WSLFJN7Q to AZWBQPQN96SS6
Data columns (total 1 columns):
reviewelpfulnessbyuserid    864 non-null float64
dtypes: float64(1)
memory usage: 12.8+ KB
None

print(df.head())

      product    reviewuserId                         reviewprofileName  \
0  B003AI2VGA  A141HP4LYPWMSR          Brian E. Erland "Rainbow Sphinx"   
1  B003AI2VGA  A328S9RN3U5M68                                Grady Harp   
2  B003AI2VGA  A1I7QGUDP043DG                 Chrissy K. McVay "Writer"   
3  B003AI2VGA  A1M5405JH9THP9                              golgotha.gov   
4  B003AI2VGA   ATXL536YX71TR  KerrLines ""MoviesMusicTheatre""   

   reviewelpfulness  reviewscore  reviewtime  \
0               1.0            3  1182729600   
1               1.0            3  1181952000   
2               0.8            5  1164844800   
3               1.0            3  1197158400   
4               1.0            3  1188345600   

                                       reviewsummary  \
0  There Is So Much Darkness Now ~ Come For The M...   
1  Worthwhile and Important Story Hampered by Poo...   
2                      This movie needed to be made.   
3                  distantly based on a real tragedy   
4  What's going on down in Juarez and shining a l...   

                                          reviewtext  
0  Synopsis: On the daily trek from Juarez Mexico...  
1  THE VIRGIN OF JUAREZ is based on true events s...  
2  The scenes in this film can be very disquietin...  
3  THE VIRGIN OF JUAREZ (2006)
directed by K...  
4  Informationally this SHOWTIME original is esse...

print(df_new_2.head())

                reviewelpfulnessbyuserid
reviewuserId                            
A100Y8WSLFJN7Q                       NaN
A103VZ3KDF2RT5                  0.555556
A1041HQGJDKFG5                  0.000000
A10FBJXMQPI0LL                  0.333333
A10LIHFA4SSK3F                  0.000000

现在错误消息msg看起来像这样：

File "pandas\hashtable.pyx", line 694, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12245)
KeyError: 'reviewuserId'

打印完这些信息后，我只需添加以下内容即可解决问题： df_new_2 = df_new.to_frame().reset_index()