Pandas creating a conditional column based on the value of another column

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

Space Impact · Accepted Answer · 2018-09-20 11:35:51Z

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

edited Sep 20, 2018 at 11:35

answered Sep 20, 2018 at 11:13

Space Impact

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3 Comments

nandneo Over a year ago

Please update your answer, it should be df1.set_index('index', drop=True, inplace=True) and df2.set_index('index', drop=True, inplace=True) in order to get the desired output shown.

Space Impact Over a year ago

@Nand Checked in pandas 0.23.4 drop=True is not needed.

AsdAsd Over a year ago

wonderful!, this is exactly what i needed,had to do a simple column name change for it to work in my case

Rahul Agarwal · Accepted Answer · 2018-09-20 11:11:06Z

0

This will work

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

or

df2.loc[df1.index]

answered Sep 20, 2018 at 11:11

Rahul Agarwal

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1 Comment

AsdAsd Over a year ago

merge and loc added more columns than i needed, thanks, but update() did the trick for me

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