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2012-05-09T22:35:08.537
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This sounds like a fine job for functional approach. At the end there is a full working example, but I just want to emphasize the elegance and simplicity of the core function, written in FP style: <pre><code>def find_best_two_months(orders): first = lambda x: x[0] second = lambda x: x[1] orders_by_year_and_month = [ ("%04d-%02d" % (date.year, date.month), amount) for date, amount in orders] sorted_orders = sorted(orders_by_year_and_month, key=first) totals_by_month = [ (ym, sum(map(second, groupped_orders))) for ym, groupped_orders in groupby(sorted_orders, key=first)] totals_two_months = [ ( "%s - %s" % (m1[0], m2[0]), m1[1]+m2[1] ) for m1, m2 in zip(totals_by_month, totals_by_month[1:]) ] return max(totals_two_months, key=second) </code></pre> <hr> Here is a full working example with comments: <pre><code>#!/usr/bin/python from random import randint from datetime import date, timedelta from itertools import groupby """ finding best two months the functional way """ def find_best_two_months(orders): """ Expect a list of tuples of form (date_of_order, amount): [ (date1, amount1), (date2, amount2), ...] """ " helper functions for extracting first or second from tuple " first = lambda x: x[0] second = lambda x: x[1] " converts [(date, amount)] -> [(YYYY-MM, amount)] " orders_by_year_and_month = [ ("%04d-%02d" % (date.year, date.month), amount) for date, amount in orders] " Sorts by YYYY-MM. This step can be omitted if orders were already sorted by date" sorted_orders = sorted(orders_by_year_and_month, key=first) " Compresses orders from the same month, so ve get [(YYYY-MM), total_amount_of_orders]" totals_by_month = [ (ym, sum(map(lambda x:x[1], groupped_orders))) for ym, groupped_orders in groupby(sorted_orders, key=first)] " Zips orders to two month periods" totals_two_months = [ ("%s - %s" % (m1[0], m2[0]), m1[1]+m2[1]) for m1, m2 in zip(totals_by_month, totals_by_month[1:]) ] " Returns two-month period with maximum total amount. If there were many periods with max amount, only the first is returned " return max(totals_two_months, key=second) """ this code is for generating random list of orders and is not a part of the solution """ MIN_AMOUNT=70 MAX_AMOUNT=500 MAX_DAY_SPREAD=5 def gen_order(last_date): """ returns (order_date, amount) """ days = timedelta() return ( last_date+timedelta(days=randint(0, MAX_DAY_SPREAD)), # new date randint(MIN_AMOUNT, MAX_AMOUNT)) # amount def gen_orders(total, start_date): orders = [] last_date = start_date for i in range(total): order = gen_order(last_date) orders.append(order) last_date = order[0] return orders if __name__ == "__main__": orders = gen_orders(300, date(2010,1,1)) print find_best_two_months(orders) </code></pre>
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