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You cleaned a file three weeks ago, someone asks how you fixed the missing region codes, and you genuinely cannot remember.
What you'll have at the end
A short changelog listing every transformation, the reason for it, and the row count before and after, saved beside the data.
You need
A raw data export you're about to clean, or already partway through cleaning, and a folder or shared drive where you can save one extra small file beside it.
Not covered
Deciding which specific rule to use for a messy column, such as which missing-value strategy fits best, and building a full data dictionary describing every field's expected type. This covers only the running record of what you did and why.
Leans on
The missing-value rule nobody wrote down for this column
when the real problem is deciding which missing-value rule to use for one column, not building the log itself, that recipe writes the rule this one just records.
Give a new export a sanity check
run that check before you start cleaning; the log this recipe builds only records what you did after you've already decided the export is trustworthy enough to work with.
Checked 26 Aug 2026
Part of the Data Cleaning and Validation for Analysts cookbook