There is a Pandas dataframe: userId movieId rating timestamp 0 1 31 2.5 1260759144 1 1 1029 3.0 1260759179 2 1 1061 3.0 1260759182 3 1 1129 2.0 1260759185 4 1 1172 4.0 1260759205 Calculate the average lifetime of users. The lifetime is the difference between the maximum and minimum values of the "timestamp" column for a given "userId".

import pandas as pd
import datetime
import numpy as np

df_ratings = pd.read_csv('C:/Users/User/Downloads/ml-latest-small/ratings.csv')

def diff_pd(x):
    return x.max() - x.min()

df_ratings.groupby('userId')['timestamp'].agg([diff_pd]).mean()