Clean up, merge or convert your CSV, Excel or JSON data

Data that needs sorting out before you can use it: duplicates to remove, names or addresses to split into columns, dates, prices or phone numbers in mixed formats, several exports to merge into one list, or a file to convert between CSV, Excel and JSON so it imports cleanly into another system. I do it with a script rather than by hand, so every row gets the same treatment, and you get the clean file plus a note of what changed and how many rows it affected. If it's bigger than it looked, I'll say so and quote before doing anything extra.