将数据帧从其他数据帧中按两列进行子集

Question

I have two datasets containing names. What is the easist pythonish way to subset df2 so it contains onlys rows df1 is containing (first, last name). Thank you.

import pandas as pd

names1 = {
    'index' : [1, 2, 3], 
    'col1'  : ['John', 'Jerry', 'John'],
    'col2'  : ['Doe', 'Peters', 'Smith']
}




names2 = {
    'index' : [1, 2, 3, 4], 
    'col1'  : ['John', 'Bob','Jerry', 'John'],
    'col2'  : ['Smith', 'Lacko', 'Peters', 'Nowak'],
    'col3'  : [12, 13, 14, 15]
}


df1 = pd.DataFrame(names1).set_index(["index"])
df2 = pd.DataFrame(names2).set_index(["index"])

print(df1,'\n')
print(df2)

        col1    col2
index               
1       John     Doe
2      Jerry  Peters
3       John   Smith 

        col1    col2  col3
index                     
1       John   Smith    12
2        Bob   Lacko    13
3      Jerry  Peters    14
4       John   Nowak    15

desired output:

       col1   col2   col3
index                     
1      John   Smith    12
3      Jerry  Peters   14

Answer 1

Use reset_index before merge and then set_index :

df = df2.reset_index().merge(df1).set_index('index')
print (df)
        col1    col2  col3
index                     
1       John   Smith    12
3      Jerry  Peters    14

because only merge lost original index values:

print (df2.merge(df1))
    col1    col2  col3
0   John   Smith    12
1  Jerry  Peters    14