Tính giá trung bình

# Create a groupby object and pass the monthly cohort and cohort index as a list
grouping = online.groupby([____, ____]) 

# Calculate the average of the unit price column
cohort_data = grouping[____].____()

# Reset the index of cohort_data
cohort_data = cohort_data.____()

# Create a pivot 
average_price = cohort_data.____(index=____, columns=____, values=____)
print(average_price.round(1))