Pandas, for each unique value in one column, get unique values in another column

Question

I have a dataframe where each row contains various meta-data pertaining to a single Reddit comment (e.g. author, subreddit, comment text).

I want to do the following

Answer 1

Using groupby.agg() "aggrgeate" function:

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DataFrameGroupBy.agg(arg, *args, **kwargs): aggregate using one or more operations over the specified axis. Function to use for aggregating the data. If a function, must either work when passed a DataFrame or when passed to DataFrame.apply

df = pd.DataFrame({'numbers': [1, 2, 3, 6, 9], 'colors': ['red', 'white', 'blue', 'red', 'white']}, columns=['numbers', 'colors'])

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df.groupby('colors', as_index=True).agg({'numbers' : {"unique" : lambda x: set(x),
                                                      "nunique" : lambda x : len(set(x))}})