Omid - Challenge 111

data-challenges
advanced-exercises
🔰 In the historical sales table, extract the dates where the total sales value is greater than the total on the previous date.
Published

March 24, 2026

Illustration for Omid - Challenge 111

Challenge Description

🔰 In the historical sales table, extract the dates where the total sales value is greater than the total on the previous date.

Solutions

library(tidyverse)
library(readxl)

path = "files/CH-111 iNCREASED SALES.xlsx"
input = read_excel(path, range = "B2:D25")
test  = read_excel(path, range = "H2:H6")

result = input %>%
  summarise(sales = sum(Sales), .by = Date) %>%
  filter(sales > lag(sales)) %>%
  select(Dates = Date)

identical(result, test)
# [1] TRUE

  • Logic:

    • Reads the workbook ranges needed for the challenge

    • Aggregates or ranks values at the relevant grouping level

  • Strengths:

    • The R solution stays close to the workbook rule and keeps the transformation compact.

  • Areas for Improvement:

    • The code assumes the sheet structure and source ranges remain stable.

  • Gem:

    • The strongest part of the solution is choosing the right intermediate representation before shaping the final output.
import pandas as pd

path = "CH-111 iNCREASED SALES.xlsx"
input = pd.read_excel(path, usecols = "B:D", skiprows = 1, nrows = 24)
test  = pd.read_excel(path, usecols = "H", skiprows = 1, nrows = 4)
                      
result = input.groupby("Date").sum()
result = result[result["Sales"] > result["Sales"].shift(1)].reset_index()
result = result.drop(columns=["Sales", "Product"])

print(result["Date"].equals(test["Dates"])) # True

  • Logic:

    • Reads the workbook ranges needed for the challenge

    • Aggregates or ranks values at the relevant grouping level

  • Strengths:

    • The Python version follows the same rule in a direct dataframe-oriented implementation.

  • Areas for Improvement:

    • The code assumes the workbook layout remains stable, so any sheet redesign would require small adjustments.

  • Gem:

    • The implementation stays close to the original workbook rule instead of adding unnecessary abstraction.

Difficulty Level

This task is moderate:

  • The business rule is readable, but the workbook still requires careful implementation to reach the expected layout.