Categories are only useful when there are few enough of them to read. A Date column in a year of transactions holds up to 365 distinct values, and nobody wants 365 row labels. Grouping collapses a fine-grained field into a handful of buckets, right inside the pivot, without touching the source. It works on dates and on numbers.
How do you group dates and numbers in a pivot table?
For dates, right-click any date label in the pivot ▸ Group (ribbon: PivotTable Analyze ▸ Group Field, access key Alt, JT, G). A dialog lets you tick any combination of Seconds, Minutes, Hours, Days, Months, Quarters, Years. Tick Quarters and 200 daily rows collapse into Q1 to Q4. Tick Years and Quarters and Months together and Excel builds a clean nested hierarchy (Year ▸ Quarter ▸ Month). It also creates synthetic fields ("Years", "Quarters") that then appear in the Field List and drag around like any other field. That's how a transaction log becomes a monthly or quarterly report in two clicks.
Advertisement
There's one hard prerequisite, and it's a frequent failure. The dates must be real dates (numeric serial values), and text that only looks like a date won't group. If Group is greyed out or errors with "Cannot group that selection," your "dates" are text. Fix them at the source before grouping, with DATEVALUE or a clean import, the way you did in Formulas II. Modern Excel also often auto-groups a date field the instant you drop it into Rows, adding Months/Quarters/Years without asking. If you don't like that, turn it off under File ▸ Options ▸ Data ▸ "Disable automatic grouping of Date/Time columns."
The same command bins a numeric row field into equal-width ranges. Put Order Value in Rows, right-click a number ▸ Group, and set "Starting at", "Ending at" and "By" (the bin width). "By 100, starting at 0" turns a scatter of order sizes into 0–99, 100–199, 200–299, …. That's an instant histogram-ready distribution. It's also the basis of the frequency views you'll chart when you reach dashboards.
Why does grouping one pivot change another?
Grouping is a property of the cache, and it surprises everyone. It belongs to the shared pivot cache underneath, so every pivot built on that cache shares it. If two pivots were built from the same source cache and you group dates into quarters on one, the other regroups into quarters too. That can break a report you thought was independent, and often there's no sign that anything changed.
If you really need two different groupings of the same data, you have to force separate caches. Build the second pivot from the source afresh through the older PivotTable Wizard, or duplicate the data. It's a trade-off, and it comes up again in the common mistakes. To undo grouping, right-click ▸ Ungroup (Alt, JT, U).