This property can only be set by accessing the collection object and using its various methods such as Add. The property to access the collection object itself is read-only; the collection itself is read/write.
// This groups the items in the view by the property "Category"
PropertyGroupDescription groupDescription = new PropertyGroupDescription();
groupDescription.PropertyName = "Category";
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)