https://www.datacamp.com/community/blog/python-pandas-cheat-sheet
https://s3.amazonaws.com/assets.datacamp.com/blog_assets/PandasPythonForDataScience.pdf
https://github.com/pandas-dev/pandas/blob/master/doc/cheatsheet/Pandas_Cheat_Sheet.pdf
https://github.com/chendaniely/scipy-2017-tutorial-pandas
https://www.datacamp.com/community/tutorials/pandas-tutorial-dataframe-python
http://datasciencefree.com/pandas.pdf
https://github.com/donnemartin/data-science-ipython-notebooks/blob/master/pandas/pandas.ipynb