Ask HN: Project Euler-Type Challenges for Data Science / Analysis?

I've used DataCamp a few years ago to get started with data analysis in Python and R. Learning to code through the browser, and "get this answer right" in order to advance the course you're taking is a great way to mix theory and practice. Recently, I've discovered Project Euler, and fell in love with its format.

Is anyone aware of similar short-form, challenge-type websites out there, focusing on data science / analysis? Using real datasets to answer specific questions, possibly with many in the "very hard" end of the spectrum.