new_for_romi['romi'] = new_for_romi['ltv'] / new_for_romi['cac']
romi = new_for_romi.pivot_table(
        index='first_order_month',
        columns='cohort_lifetime',
        values='romi',
        aggfunc='mean')
romi.index = romi.index.strftime("%m/%Y")
plt.figure(figsize=(13, 9))
plt.title('ROMI')
sns.heatmap(romi, annot=True, fmt='.1f', linewidths=1, linecolor='gray')