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Unit 2 · Cleaning and Shaping

Missing values, wrong types, duplicates and the order you fix them in.

  1. 1What Dirty Data Looks LikeThe four problems you will meet in almost every real file.
  2. 2Missing ValuesFind them, then decide between dropping and filling on purpose.
  3. 3Fixing TypesEverything out of a file is text, and text sorts and adds in the wrong way.
  4. 4Removing DuplicatesDeciding what counts as the same row is most of the work.
  5. 5Filtering RowsSelecting the rows you meant, and noticing how many you dropped.
  6. 6Sorting and RankingOrder by the value you mean, and remember that sorted returns a new list.