Data Type

A data type tells the computer what kind of value a column holds and what operations make sense on it — for instance integer, decimal number, text string, date, or boolean (true/false). The type matters because “3” as text and 3 as a number behave very differently: you can add numbers but not text.

A huge share of cleaning bugs come from wrong types: a column of prices read as text won't sum correctly, dates stored as strings won't sort by calendar, and a ZIP code read as a number loses its leading zero. Checking and fixing types is usually the very first cleaning step.