Excel BI - Excel Challenge 876

excel-challenges

excel-formulas

🔰 Work out the running total.

Published

March 24, 2026

Illustration for Excel BI - Excel Challenge 876

Challenge Description

🔰 Work out the running total. If the numbers are a streak which is a continuous block of identical values, the values will change like this

Solutions

library(tidyverse)
library(readxl)

path <- "Excel/800-899/876/876 Running Total.xlsx"
input <- read_excel(path, range = "A1:B41")
test <- read_excel(path, range = "C1:C41")


result = input %>%
  mutate(streak = cumsum(Value != lag(Value, default = first(Value)))) %>%
  mutate(n = row_number(), .by = streak) %>%
  mutate(
    adj = if_else(Value %% 2 == 0, Value - 2 * (n - 1), Value + (n - 1)),
    running_total = cumsum(adj)
  )

all.equal(result$running_total, test$`Answer Expected`)
# [1] TRUE

Logic: Read the workbook ranges needed for the challenge; Derive the required intermediate columns; Aggregate or rank the data at the required grouping level.
Strengths: The code maps the workbook rule into a compact, reproducible pipeline.
Areas for Improvement: The solution assumes the workbook layout and selected ranges remain stable, so any structural change in the sheet would require small adjustments.
Gem: The elegant part is how little code is needed once the correct intermediate representation is chosen.

import pandas as pd

path = "Excel\\800-899\\876\\876 Running Total.xlsx"
input = pd.read_excel(path, usecols="A:B", nrows = 51)
test = pd.read_excel(path, usecols="C", nrows = 51)

g = input["Value"].ne(input["Value"].shift()).cumsum()
input["running_total"] = (
    input["Value"]
    + (input["Value"] % 2) * (input.groupby(g).cumcount())
    - (input["Value"] % 2 == 0) * 2 * (input.groupby(g).cumcount())
).cumsum()

print(input["running_total"].equals(test["Answer Expected"])) # True

The Python version follows the same grouped logic and keeps the transformation explicit in a dataframe pipeline.

Difficulty Level

Easy / Medium

The business rule is clear, though the workbook still needs a few transformation steps to reach the expected output.