Medium
Thursday, October 1Challenge 01
Customer Import Rescue
Clean a customer export before it is allowed into a CRM.
Starts when you’re readyFull challenge
Dirty Data Lab™
Nine October data-cleaning puzzles. Think Sudoku, but for messy spreadsheets.
Clean the sheet directly in your browser, check your work instantly, and keep going until every cell is right. A new challenge lands every Monday and Thursday.
Mondays + Thursdays Save streaks with a free Lab profile
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Pick a challenge and start cleaning.
No download required. Your score updates after you check your work.
Medium-Hard
Monday, October 5 · timed sprintVendor Master Merge
Accounting has two versions of several vendors. The newest record wins, but a blank field on the newest row must inherit the last known nonblank value from the older match.
Show cleanup rules
- Normalize vendor_id, vendor names, city/state, tax IDs and phone numbers.
- Format tax IDs as NN-NNNNNNN and phones as NNN-NNN-NNNN.
- Normalize updated_at to YYYY-MM-DD and status to Active or Inactive.
- For duplicate vendor_id values, keep the newest updated_at row.
- If the newest duplicate has a blank field, fill it from the older matching vendor.
- Sort by vendor_id ascending.
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October board
All nine challenges
Medium-Hard
Monday, October 5Challenge 02
Vendor Master Merge
Turn a vendor master with duplicate records into one reliable source of truth.
Starts when you’re readyFull challenge
Hard
Thursday, October 8Challenge 03
Invoice Reconciliation
Reconcile invoice rows where formatting hides duplicates and credits.
Starts when you’re ready Opens Thursday, October 8
Hard
Monday, October 12Challenge 04
CRM Collision Course
Resolve duplicate CRM contacts using normalized identity fields and recency.
Starts when you’re ready Opens Monday, October 12
Very Easy
Thursday, October 15Challenge 05
The Five-Minute Cleanup
A deliberate breather: one blank row, one duplicate, and simple formatting.
Starts when you’re ready Opens Thursday, October 15
Medium-Hard
Monday, October 19Challenge 06
Order Export Maze
Clean line-item data, expose duplicate keys, then prove the revenue total.
Starts when you’re ready Opens Monday, October 19
Hard
Thursday, October 22Challenge 07
Property Roster Audit
Clean a lease roster and recover the real active-rent roll.
Starts when you’re ready Opens Thursday, October 22
Medium-Hard
Monday, October 26Challenge 08
UTM Aggregation Puzzle
Normalize campaign dimensions, then combine rows that only look different.
Starts when you’re ready Opens Monday, October 26
Hard
Thursday, October 29Challenge 09
Month-End Data Audit
Finish October with a finance-style audit where every cleanup rule matters.
Starts when you’re ready Opens Thursday, October 29
Have a real file instead?
The Lab is practice. Clean That Sheet is for the spreadsheet that actually has to go out the door.
Clean a real spreadsheet Take the habit into Google Sheets
Practice here. Preflight real sheets with CTS Guard.
Clean That Sheet Guard checks the active Google Sheet for duplicates, missing data, formatting issues and other handoff problems before you share or import it.