pandas - python : How to merge two data frames where the values are not unique

Question

我有两个数据框，

import pandas as pd
a = pd.DataFrame( { 'port':[1,1,0,1,0], 'cd':[1,2,3,2,1], 'date':["2014-02-26","2014-02-25","2014-02-26","2014-02-26","2014-02-25"] } )
b = pd.DataFrame( { 'port':[0,1,0,1,0], 'fac':[2,1,2,2,3], 'date': ["2014-02-25","2014-02-25","2014-02-26","2014-02-26","2014-02-27"] } )

我需要做的是获取每个日期端口对，例如端口 0 和日期 2014-02-25，查找 b 中的 fac 值，然后将其填充到 a 中的新列中。因此，输出应该类似于

port cd date         fac 
1    1  "2014-02-26" 2
1    2  "2014-02-25" 1
... (so on) ...

我尝试合并日期和端口上的帧，但出现错误，我认为这是由于数据帧大小不同的事实 - 而且我并不认为它会起作用.

Answer 1

如果您希望合并两个数据帧，您应该使用 merge

import pandas as pd
a = pd.DataFrame( { 'port':[1,1,0,1,0], 'cd':[1,2,3,2,1], 
         'date':["2014-02-26","2014-02-25","2014-02-26","2014-02-26","2014-02-25"]})

b = pd.DataFrame( { 'port':[0,1,0,1,0], 'fac':[2,1,2,2,3], 
         'date': ["2014-02-25","2014-02-25","2014-02-26","2014-02-26","2014-02-27"]})

df = a.merge(b)
print (df)

输出:

  port  cd  date       fac
0   1   1   2014-02-26  2
1   1   2   2014-02-26  2
2   1   2   2014-02-25  1
3   0   3   2014-02-26  2
4   0   1   2014-02-25  2