Omid - Challenge 144

data-challenges
advanced-exercises
🔰 From the provided ‘transactions’ table, filter the first transaction for each month.
Published

March 24, 2026

Illustration for Omid - Challenge 144

Challenge Description

🔰 From the provided “transactions” table, filter the first transaction for each month.

Solutions

library(tidyverse)
library(readxl)

path = "files/CH-144 First transaction in each month.xlsx"
input = read_excel(path, range = "C2:E27")
test  = read_excel(path, range = "G2:I6")

result = input %>%
  mutate(month = month(Date)) %>%
  filter(row_number() == 1, .by = month) %>%
  select(-month)

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-144 First transaction in each month.xlsx"
input = pd.read_excel(path, usecols="C:E", skiprows=1, nrows=26)
test = pd.read_excel(path, usecols="G:I", skiprows=1, nrows=4).rename(columns=lambda x: x.split('.')[0])

result = input.assign(month=input['Date'].dt.month).groupby('month').head(1).drop(columns='month').reset_index(drop=True)

print(result.equals(test))  # True

  • Logic:

    • Reads the workbook ranges needed for the challenge

    • Aggregates or ranks values at the relevant grouping level

    • Builds the intermediate columns that drive the final result

  • 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.