Summarize data by grouping it into buckets based on one or more categories.
Large tables of data can be difficult to understand at a glance. Rolling them up into summary tables makes them much more understandable. In Excel you might use something like a pivot table or in SQL you might use a GROUP BY.
Using a “Group By” object you can choose which columns to use to roll-up your data as well as whether you want to get a count sum or average in the resulting summary. You can also use a “Pivot” object to rotate some of the columns into rows to make it even more legible.