Extras section is a bit thin

[projectgus]

The current Extras chapters ("Alternative Approaches" & "Open Data") provide a few pointers and links to things to check out, but it'd be awesome if there were some more cool data projects (or challenges) in the Extras section. :)

Great idea, but maybe it makes sense to close this issue in lieu of more specific suggestions? Off the top of my head:

• SQL intro
• Learning and study strategies for data science (or coding/CS in general), including mnemonics, Anki and SRS, etc.
• Data resources
• Some more advanced statistical methods and examples (significance tests, correlation, regression)
• Advanced visualization methods and examples (transformations, maps, etc.)
• Advanced data frame manipulations with Pandas (e.g. SQL-like joins, etc.)
• …