Check if a row exists in one data frame in another data frame

Question

I have a data frame A, like this:

And another data frame B, which looks like this:

I want to add the column "Exist" in data frame A, so that if the user and the movie exist in data frame B, then "Exist" is True, otherwise it is False. So A should look like this:

Answer 1

You can use mergewith a parameter indicator, then remove the column Ratingand 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