A viewer of a data visualization can select the value for grouping the data in the visualization.

If a data visualization is configured with alternative group-by values, a viewer can pick which value to apply. No editing rights are required.

Note: Instructions for configuring alternative group by are included in the data options topics for the relevant data visualizations.
Toggle the visibility of the selector for group-by values by selecting Change group by in the data visualization's More actions menu. An editor of the visualization can set whether the selector is visible or hidden by default.
The toggle for showing or hiding the group-by value selector in the data visualization More options menu.
All data visualizations that support group by also let viewers select the group-by value, except for pivot tables. For all such data visualizations except bar visualizations, you have only a single group-by value to select.
Group-by selector for time series visualizations
Bar visualizations also let you choose a stack-by value.
Bar visualization group by selector for both group by and stack by.