Omid - Challenge 148

data-challenges
advanced-exercises
🔰 Filter Dates!
Published

March 24, 2026

Illustration for Omid - Challenge 148

Challenge Description

🔰 Filter Dates!

Solutions

library(tidyverse)
library(readxl)

path = "files/CH-148 Filter Dates.xlsx"
input = read_excel(path, range = "C2:E17")
test  = read_excel(path, range = "G2:I11")

result = input %>%
  mutate(
    first = Date == min(Date, na.rm = TRUE),
    last  = Date == max(Date, na.rm = TRUE),
    middle = Date == Date[ceiling(length(Date)/2)],
    .by = Customer
  ) %>%
  filter(first | last | middle) %>%
  select(Date, Customer, Qty)

all.equal(result, test, check.attributes = FALSE)
#> [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-148 Filter Dates.xlsx"
input = pd.read_excel(path, usecols="C:E", skiprows=1, nrows=15)
test = pd.read_excel(path, usecols="G:I", skiprows=1, nrows=9).rename(columns=lambda x: x.split('.')[0])

result = input.groupby('Customer').apply(
    lambda x: x.loc[x['Date'].isin([x['Date'].min(), x['Date'].max(), x['Date'].iloc[len(x) // 2]])]
).reset_index(drop=True)

print(test.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.