view view groupby subview ?prop ...?
Returns a new view derived from view as described below. This is almost an inverse of [view view flatten subview].
The argument subview must be the name of an existing property in view that is itself a view. The properties of the returned view will be the properties prop followed by the property subview. The properties of property subview in the returned view will be all the properties of view not named among the prop arguments. Any properties of subview as defined in view do not appear in the returned view.
There is one row in the returned view for every unique combination of values of the prop properties in view. For each row in view with that combination, a row will be added to the subview view containing the values of the properties not named as prop arguments.
NOTE: A variant of this command that created subview in the returned view, and did not require it to already exist in view would be much more useful. That would be a true inverse of [view view flatten]