AFAIK, Kaggle (https://en.wikipedia.org/wiki/Kaggle https://en.wikipedia.org/wiki/Kaggle) is the go-to site to hone your skills in data science using challenges

AFAIK, Kaggle (https://en.wikipedia.org/wiki/Kaggle https://en.wikipedia.org/wiki/Kaggle) is the go-to site to hone your skills in data science using challenges, similar to Project Euler. The nice thing is that not only you can make money if you solve a challenge (unlikely for starters) you can build a profile that can be valuable in job applications.