How to specify columns to be merged using pd.merge

Question

Trying to use pd.merge , I don’t understand how to specify the column we want to add in an other dataframe.

Is it possible?

Below is what I would Like to do :

DF1

DF2

index	ID	Name	Date
0	1	ART	09-13-2022
1	21	DRAW	09-13-2022
1.1	7	GAME	09-13-2022
…	5	GAME	09-13-2022
115	8	GAME	09-13-2022

The output would be :

index	ID	Style	Name
0	1	a	ART
1	21	z	DRAW
2	7	e	GAME

I have tried :

Output = DF1.merge(DF2, on = 'ID', how='left')

Which works but it merge all column and not only the name column.

How can I specify 1 or several column(s) using merge? In this example, we need to specify that we want only Name column to be added to DF1.

Asked By: TourEiffel

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Answer 1

Slice DF2 to only keep the key(s) and the column(s) to add:

Output = DF1.merge(DF2[['ID', 'Name']], on='ID', how='left')

output:

    index   ID  Name
0       0    1   ART
1       1   21  DRAW
2       2    7  GAME

Answered By: mozway

Answer 2

You can change the columns associated to your dataframes within the merge itself, for example

Output = DF1.merge(DF2[['ID','Name']], on = 'ID', how='left')

This will only take the two columns you want into the merge and because ‘Name’ is an additional column it will join this onto DF1

Answered By: Hillygoose

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