Updates to the pandas practical/talk

Additions:

• discussion of pandas types

Clarifications:

• improved explanation of why one would want to extract only numeric columns or create dummy variables

added 28 commits

• 64f8fe52...8f23ab03 - 27 commits from branch master
• 5fc3b2ce - discuss types

Compare with previous version

marked this merge request as ready

merged

mentioned in commit 74bd46ee