#0154

Cumulative Sales by Customer

MediumPandas25 min20 XP

Problem

Given a dataframe with customer, date, and amount, return it sorted by customer/date with a cumulative_amount column per customer.

Why This Matters

Running totals are used in customer value, retention history, inventory movement, and financial reporting.

Function Signature

def add_cumulative_sales(df):

Examples

Example 1

Inputcustomer A has amounts 10 then 5; customer B has 7

OutputA cumulative values 10, 15; B cumulative value 7

The running total resets for each customer.

Constraints

Return the exact requested value.
Handle empty or small inputs when the prompt allows them.
Keep the code readable and deterministic.

CodePython

import pandas as pd

def add_cumulative_sales(df):
    """
    Input example: customer A has amounts 10 then 5; customer B has 7
    Return: A cumulative values 10, 15; B cumulative value 7
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return df

import pandas as pd

def add_cumulative_sales(df):
    """
    Input example: customer A has amounts 10 then 5; customer B has 7
    Return: A cumulative values 10, 15; B cumulative value 7
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return df

Visible browser tests run here when available.

Testcases1 visible / 3 hidden categories

Core example

Inputcustomer A has amounts 10 then 5; customer B has 7

ExpectedA cumulative values 10, 15; B cumulative value 7

The running total resets for each customer.

Hidden Test Categories

empty or smallest inputduplicates or repeated valueslarger realistic input