Mastering pandas - Second Edition

The groupby operation

Through a groupby function, a chain of actions gets executed: splitting, applying, and combining. Splitting segments each category from the desired grouping variable to perform further operations with it. Then, functions can be individually applied across each of these split groups. These functions might involve aggregation (sum across a group or mean across a group), transformation (filling NAs within a group or sorting), filtration (applying conditions within a group to drop rows), or even a combination of these three operations. Finally, the results obtained after the functions are applied across each of the split groups are combined together.

Let's use sample data from a fictitious global retailer. The data available ...