Pandas Essentials – Apply

I often find people who are just starting out using pandas struggling to grasp when they should be using axis=0 and axis=1. While I go into a lot more detail with examples in the Youtube video above, you should keep this in mind.

When you use axis=0, pandas only looks at the value being passed, but when you use axis=1, by default it assumes a pandas Series being passed, so it looks for the index. So when you write a function which references multiple columns and use apply, use axis=1 and remember that it considers each row as a pandas Series, with the column names in the index.