Omid - Challenge 257

data-challenges
advanced-exercises
🔰 Result Dates Challenge 257: Date Calculation!
Published

March 24, 2026

Illustration for Omid - Challenge 257

Challenge Description

🔰 Result Dates Challenge 257: Date Calculation!

Solutions

library(tidyverse)
library(readxl)

path = "files/200-299/257/CH-257 Date Calculation.xlsx"
test  = read_excel(path, range = "B2:B14") %>% 
  mutate(Dates = as.Date(Dates))

eom = ceiling_date(ymd(paste(2025, 1:12, 1, sep = "-")), "month") - 1
last_mondays = eom - days((wday(eom) - 2) %% 7) 

all.equal(last_mondays, test$Dates, 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 = "200-299/257/CH-257 Date Calculation.xlsx"
test = pd.read_excel(path, usecols="B", skiprows=1, nrows=12)

result = pd.DataFrame({
    "Result": [
        (d - pd.Timedelta(days=d.weekday() % 7)).to_datetime64()
        for d in pd.date_range("2025-01-31", "2025-12-31", freq="ME")
    ]
})

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

  • Logic:

    • Reads the workbook ranges needed for the challenge

    • Applies the rule iteratively until the output stabilizes

  • 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.