Cleaning Messy Data Into Something Usable

⚠️ Version note. Menu locations differ across Excel, Google Sheets and versions. The cleaning steps are universal. Last checked: 25 July 2026.

What you'll have at the end

• The definition of a tidy table (the target every clean-up aims at)
• One real messy dataset cleaned: trimmed, de-duplicated, split, typed, and gap-checked
• A repeatable cleaning checklist you run on any new data

Prerequisite

• TL-01 — Spreadsheets From Zero. You need basic formulas and cell references.
• A real, messy dataset (an export from an app, a copied web table, a survey download).

"Garbage in, garbage out" is a spreadsheet law

Every analysis (TL-02, AI-09, the charts in PS-04) assumes clean input. Feed it messy data and you get confident nonsense. Cleaning isn't glamorous, but it's where most real spreadsheet time goes and it's the difference between a chart that's true and one that's a lie you made by accident.

The target is a tidy table: one row per record, one column per variable, one value per cell, and consistent types. Everything below moves your data toward that.