Pandas gives you two new data types: Series and DataFrame. The DataFrame represents your entire spreadsheet or rectangular data, whereas the Series is a single column of the DataFrame.

Mueller chose to convert the sheets into pandas data frame and while, as he mentions in the comments, it was not necessary, but we can take the opportunity to learn a little bit of pandas too.

The simplest form of regression in Python is, well, simple linear regression. With simple linear regression, you're trying to ...