อัตราส่วนของค่าเฉลี่ยเดือนที่แล้วต่อค่าเฉลี่ยปีที่แล้ว

# Average gift last month for each donor
average_gift_last_month = gifts_last_month.____("____")["____"].____().reset_index()
average_gift_last_month.columns = ["donor_ID", "mean_gift_last_month"]

# Average gift last year for each donor
average_gift_last_year = ____
average_gift_last_year.columns = ["donor_ID", "mean_gift_last_year"]

# Add average gift last month and year to basetable
basetable = pd.merge(____, ____, on="____", how="____")
basetable = pd.merge(____, ____, on="____", how="____")

# Calculate ratio of last month's and last year's average
basetable["ratio_month_year"] = basetable["____"] / basetable["____"]
print(basetable.head())