19. Aggregate Sales Data by Time Period
1. Hello, World!
2. Rename Photos by Capture Date
3. Organize Downloads Folder by File Type
4. Delete Old Log Files Automatically
5. Find Duplicate Files Using MD5 Hashing
6. Generate Comprehensive File Inventory
7. Parse Web Server Logs for Performance Metrics
8. Extract Emails, URLs, and Phone Numbers from Text
9. Track Daily and Monthly Active Users from Apache Logs
10. Generate Formatted Text Reports with Column Alignment
11. Analyze Sales Transactions and Generate Revenue Reports
12. Clean and Validate CSV Data
13. Convert JSON API Responses to CSV
14. Parse and Validate Configuration Files
15. Build a CLI Calculator with Argument Parsing
16. Parse and Display Weather Data from JSON
17. Build a Simple Inventory System with Classes
18. Generate Markdown Table from CSV Data
19. Aggregate Sales Data by Time Period
20. Recursive Directory Size Calculator with Filtering
21. Parse and Transform XML Configuration Files
22. Find and Replace Across Multiple Files
23. Build a Simple Template Engine
24. CSV Data Validator with Business Rules
25. Build a Multi-Format Log Analyzer

Challenge

Problem

Business analytics often requires aggregating time-series data into meaningful periods for reporting and decision-making. This drill teaches you to parse dates, group transactions by month, calculate aggregate statistics, and format currency. You'll learn date manipulation, hash-based grouping, aggregation functions, and business reporting—essential skills for building dashboards, analytics tools, and financial reports.

Difficulty: Intermediate

Instructions

  1. Read sales transactions from sales.csv (Date, Product, Amount)
  2. Parse dates and group transactions by month (YYYY-MM format)
  3. For each month, calculate:
    • Total sales amount
    • Number of transactions
    • Average transaction value
  4. Sort months chronologically
  5. Print monthly report:
    'MONTHLY SALES REPORT'
    '=' * 50
    'Month: YYYY-MM'
    ' Transactions: X'
    ' Total Sales: $X,XXX.XX'
    ' Average: $XXX.XX'
    (blank line between months)
  6. Print summary:
    '-' * 50
    'OVERALL SUMMARY'
    'Total Transactions: X'
    'Total Sales: $X,XXX.XX'
    'Average per Transaction: $XXX.XX'

Files

Editable
Read-only

Hints

Hint 1

Date.parse(string) converts date string to Date object

Hint 2

date.strftime('%Y-%m') formats date as 'YYYY-MM'

Hint 3

Hash.new { |h, k| h[k] = [] } creates hash with array default values

Hint 4

array.sum calculates total of all elements

Hint 5

hash.keys.sort sorts month strings alphabetically (which is chronological)

Hint 6

hash.values.flatten combines all arrays into one

Hint 7

Format decimals: '%.2f' % number

Hint 8

Add commas: reverse string, insert commas every 3 digits, reverse back

Provided Files (Read-only)

1. Three months of sales

Input: 
analyze_sales('sales.csv')
Expected Output: 
MONTHLY SALES REPORT
==================================================
Month: 2024-01
  Transactions: 3
  Total Sales: $1,419.97
  Average: $473.32

Month: 2024-02
  Transactions: 3
  Total Sales: $1,779.97
  Average: $593.32

Month: 2024-03
  Transactions: 4
  Total Sales: $1,869.96
  Average: $467.49

--------------------------------------------------
OVERALL SUMMARY
Total Transactions: 10
Total Sales: $5,069.90
Average per Transaction: $506.99

2. Single month

Input: 
analyze_sales('sales.csv')
Expected Output: 
MONTHLY SALES REPORT
==================================================
Month: 2024-05
  Transactions: 3
  Total Sales: $450.00
  Average: $150.00

--------------------------------------------------
OVERALL SUMMARY
Total Transactions: 3
Total Sales: $450.00
Average per Transaction: $150.00

3. Multiple months with varying amounts

Input: 
analyze_sales('sales.csv')
Expected Output: 
MONTHLY SALES REPORT
==================================================
Month: 2024-06
  Transactions: 2
  Total Sales: $8,500.50
  Average: $4,250.25

Month: 2024-07
  Transactions: 3
  Total Sales: $5,501.00
  Average: $1,833.67

--------------------------------------------------
OVERALL SUMMARY
Total Transactions: 5
Total Sales: $14,001.50
Average per Transaction: $2,800.30
+ 2 hidden test cases