human
Finding common rows (intersection) in two Pandas dataframes
assistant
Here is some code to join data of dataframe `df1` with data in dataframe `df2` based on similar values of column 'user_id' in both dataframes

s1 = pd.merge(df1, df2, how='inner', on=['user_id'])

#Warning: this code generation is experimental. Please inspect the code for any bugs before executing.