https://pandas.pydata.org/pandas-docs/stable/groupby.html
https://pandas.pydata.org/pandas-docs/stable/indexing.html
http://lifelines.readthedocs.io/en/latest/index.html
https://matplotlib.org/api/axes_api.html
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.plot.html
https://gist.github.com/HHammond/2f3a5ab2aca280da986b27a8d5bc90a4