熊猫根据另一列的值创建条件列

Question

I have two df's

df1:

index    text
1        string1
2        string2
3        string3
4        a
5        string5
6        a

df2:

index    text
4        string4
6        string6

How can I replace the text 'a' in df1 with the values found in df2 based on the index, so that it shows as below.

df3:

index    text
1        string1
2        string2
3        string3
4        string4
5        string5
6        string6

Answer 1

You can use pandas update as:

df1.set_index('index',inplace=True)
df2.set_index('index',inplace=True)
df1.update(df2) #df1 is changed

Or

df1.loc[df2.index,'text'] = df2['text'] #df1 is changed

Or The output to be in df3 then

df3 = df1.copy()
df3.update(df2) #df3 is changed

All of them produces:

       text
index   
1   string1
2   string2
3   string3
4   string4
5   string5
6   string6

Answer 2

This will work

pd.merge(df1[[]], df2, left_index=True, right_index=True)

or

df2.loc[df1.index]