Omid - Challenge 143

data-challenges
advanced-exercises
🔰 Group Custom Grouping!
Published

March 24, 2026

Illustration for Omid - Challenge 143

Challenge Description

🔰 Group Custom Grouping!

Solutions

library(tidyverse)
library(readxl)

path = "files/CH-143 Custom Grouping.xlsx"
input = read_excel(path, range = "B2:C26")
test  = read_excel(path, range = "G2:H6")

result = input %>%
  mutate(wday = floor_date(Date, unit = "week", week_start = 5)) %>%
  mutate(Group = cumsum(c(1, diff(wday) != 0))) %>%
  summarize(`Total Sales` = sum(Sales), .by = Group)

all.equal(result, test)
#> [1] TRUE

  • Logic:

    • Reads the workbook ranges needed for the challenge

    • Builds the intermediate columns that drive the final result

  • 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-143 Custom Grouping.xlsx"
input = pd.read_excel(path, usecols="B:C", skiprows=1, nrows=25)
test = pd.read_excel(path, usecols="G:H", skiprows=1, nrows=4)

input['Group'] = (input['Date'] - pd.to_timedelta((input['Date'].dt.weekday - 4) % 7, unit='d')).diff().dt.days.ne(0).cumsum().astype("int64")
result = input.groupby('Group')['Sales'].sum().reset_index(name='Total Sales')

print(result.equals(test)) # 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.