Drop rows corresponding to groups smaller than specified size

Question

I have a DataFrame of answers for 100 questions_id and 50 user_id\'s. Each row represents a single question from a specific user. The ta

Answer 1

Use groupby and filter, very succinct and intended for this purpose.

df1 = df.groupby('user_id').filter(lambda x: len(x) > 100)

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For better performance, use np.unique and map:

m = dict(zip(*np.unique(df.user_id, return_counts=True)))
df[df['user_id'].map(m) > 100]