python之Pandas 合并不保留排序顺序

我正在尝试以下操作:

PoliceStations_raw=pd.DataFrame( 
[['BAYVIEW'   ,37.729732,-122.397981], 
 ['CENTRAL'   ,37.798732,-122.409919], 
 ['INGLESIDE' ,37.724676,-122.446215], 
 ['MISSION'   ,37.762849,-122.422005], 
 ['NORTHERN'  ,37.780186,-122.432467], 
 ['PARK'      ,37.767797,-122.455287], 
 ['RICHMOND'  ,37.779928,-122.464467], 
 ['SOUTHERN'  ,37.772380,-122.389412], 
 ['TARAVAL'   ,37.743733,-122.481500], 
 ['TENDERLOIN',37.783674,-122.412899]],columns=['PdDistrict','XX','YY']) 
 
 
df1=pd.DataFrame([[0,'CENTRAL'],[1,'TARAVAL'],[3,'CENTRAL'],[2,'BAYVIEW']]) 
df1.columns = ['Index','PdDistrict'] 
 
 
  Index PdDistrict 
0   0   CENTRAL 
1   1   TARAVAL 
2   3   CENTRAL 
3   2   BAYVIEW 

尽管输入了sort=False，但返回的对象合并了表格，但使用PdDistrict作为一些索引，并改变了原始表格行的顺序左数据框。

pd.merge(df1,PoliceStations_raw,sort=False) 

返回这个(注意 PdDistrict 的顺序已经改变)

  Index PdDistrict  XX        YY 
0   0   CENTRAL 37.798732   -122.409919 
1   3   CENTRAL 37.798732   -122.409919 
2   1   TARAVAL 37.743733   -122.481500 
3   2   BAYVIEW 37.729732   -122.397981 

请您参考如下方法:

您需要指定两个数据框的合并方式。默认情况下，内部联接由 merge() 模拟。但是，通过指定您想要左连接，df1 中的排序顺序将被保留。因此，您只需添加 how='left':

>>> pd.merge(df1, PoliceStations_raw, how='left') 
   Index PdDistrict         XX          YY 
0      0    CENTRAL  37.798732 -122.409919 
1      1    TARAVAL  37.743733 -122.481500 
2      3    CENTRAL  37.798732 -122.409919 
3      2    BAYVIEW  37.729732 -122.397981 

此外，sort=False 是默认行为——您无需指定。