Challenge Yourself: Websites to Hone Your Skills

I would highly recommend these two resources to challenge your data science skills.

The first one is the UCI Machine Learning Repository. 

They have tons of data sets for you to choose from and are all nicely categorized  and processed.

You can access it here: https://archive.ics.uci.edu/ml/datasets.php

The second is Kaggle.

They have competitions and you can see what others have submitted for past competitions and learn from them.

You can access it here: https://www.kaggle.com/