Omid - Challenge 261

data-challenges
advanced-exercises
🔰 Group Challenge 261: Custom Grouping!
Published

March 24, 2026

Illustration for Omid - Challenge 261

Challenge Description

🔰 Group Challenge 261: Custom Grouping!

Solutions

library(tidyverse)
library(readxl)

path = "files/200-299/261/CH-261 Custom Grouping .xlsx"
input = read_excel(path, range = "B2:C16")
test  = read_excel(path, range = "F2:H16")

group = 1
seen = character()

result = input %>% mutate(
  Group = map_int(ID, ~{
    if (.x %in% seen) {
      group <<- group + 1
      seen <<- .x
    } else {
      seen <<- c(seen, .x)
    }
    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
import numpy as np

path = "200-299/261/CH-261 Custom Grouping .xlsx"
input = pd.read_excel(path, skiprows=1, usecols="B:C", nrows=14)
test = pd.read_excel(path, skiprows=1, usecols="F:H", nrows=14).rename(columns=lambda col: col.replace('.1', ''))

def make_assign_group():
    group = [1]
    seen = set()
    def assign(id_val):
        if id_val in seen:
            group[0] += 1
            seen.clear()
        seen.add(id_val)
        return group[0]
    return assign

result = input.copy()
result['Group'] = result['ID'].apply(make_assign_group())

print(result.equals(test)) # True

  • Logic:

    • Reads the workbook ranges needed for the challenge

    • 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.