Check if rows in one dataframe exist in another dataframe

Question

I have a data frame A dfA like this:

And another data frame B dfB which looks like this:

I want to add a column 'Exist' to dfA so that if User and Movie both exist in dfB then 'Exist' is True, otherwise it is False. So dfA should become like this:

Please dont use png for data or tables, use text.

Merlin
– Merlin

2016-08-09 16:16:15 +00:00
Commented Aug 9, 2016 at 16:16 — Merlin
– Merlin, Commented Aug 9, 2016 at 16:16

jezrael · Accepted Answer · 2016-08-09 15:54:13Z

72

You can use merge with parameter indicator, then remove column Rating and use numpy.where:

df = pd.merge(df1, df2, on=['User','Movie'], how='left', indicator='Exist')
df.drop('Rating', inplace=True, axis=1)
df['Exist'] = np.where(df.Exist == 'both', True, False)
print (df)
   User  Movie  Exist
0     1    333  False
1     1   1193   True
2     1      3  False
3     2    433  False
4     3     54   True
5     3    343  False
6     3     76   True

answered Aug 9, 2016 at 15:54

jezrael

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1 Comment

Hari Over a year ago

It will be useful to indicate that the objective of the OP requires a left outer join. More details here: realpython.com/pandas-merge-join-and-concat/#how-to-merge

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