Seven-Day Revenue Per User Average | Dataford Interview Questions

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On a Meta product such as Facebook, you are given raw daily monetization events and need to compute a smoothed revenue-per-user trend. Write a function that returns the 7-day rolling average of daily revenue per user (RPU) for each calendar day.

For each event, you are given a date string in YYYY-MM-DD format, a user_id, and a revenue amount. First aggregate events by day to compute:

daily revenue = sum of all revenue on that day
daily active users = number of distinct users with at least one event on that day
daily RPU = daily revenue / daily active users

Then compute the 7-day rolling average of daily RPU over the current day and the previous 6 days. If fewer than 7 days exist so far, average over all available days.

Return a list of [date, rolling_average] pairs in ascending date order. Round each rolling average to 2 decimal places.

Formal Specification

Input: events, a list of lists where each item is [date, user_id, revenue]
Output: a list of [date, rolling_average]

Constraints

1 <= len(events) <= 10^5
date is a valid YYYY-MM-DD string
user_id is a non-empty string
0 <= revenue <= 10^6
Multiple events may exist for the same user on the same day

Function Signature

def rolling_rpu_7day(events):