Developer: RhinoScript
Summary: Demonstrates how to determine what object groups are selected usin RhinoScript.

I have a number of objects selected and I would like to know what groups these objects belong to. Is this possible using RhinoScript?

Yes, this is possible. The following sample RhinoScript demonstrates this.

 Option Explicit
 
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 ' Description
 '   Returns an array of objects group names 
 '   from selected objects.
 ' Parameters
 '   none
 ' Returns
 '   An array of object group names or vbNull if none
 '   of the selected objects belongs to a group.
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 Function SelectedGroups()
 
   ' Declare locals
   Dim arrObjects, arrGroups(), strGroup
   Dim i, nCount, bAppend
 
   SelectedGroups = Null ' Default
   nCount = -1
 
   ' Get the selected objects  
   arrObjects = Rhino.SelectedObjects
   If Not IsArray(arrObjects) Then Exit Function
 
   ' Process each object. If the object belongs to an
   ' object group and that group name is not already
   ' in arrGroups, then append it to the end.    
   For i = 0 To UBound(arrObjects)
     bAppend = False
     strGroup = Rhino.ObjectTopGroup(arrObjects(i))
     If Not IsNull(strGroup) Then
       If (nCount = -1) Then 
         bAppend = True
       ElseIf (FindGroup(strGroup, arrGroups) = -1) Then
         bAppend = True
       End If
       If bAppend = True Then
         nCount = nCount + 1
         ReDim Preserve arrGroups(nCount)
         arrGroups(nCount) = strGroup
       End If
     End If
   Next
 
   ' Return the array of group names    
   If (nCount > -1) Then SelectedGroups = arrGroups
 
 End Function
 
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 ' Description
 '   Searches an array of strings
 ' Parameters
 '   strGroup - the name to look for
 '   arrGroups - the array to search
 ' Returns
 '   >= 0 if strGroup is found in arrGroups
 '   -1 otherwise      
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 Function FindGroup(strGroup, arrGroups)
   Dim i
   FindGroup = -1 ' Default
   For i = 0 To UBound(arrGroups)
     If (StrComp(strGroup, arrGroups(i), 1) = 0) Then
       FindGroup = i
       Exit Function
     End If
   Next
 End Function
 
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 ' Test our SelectedGroups function
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 Sub TestSelectedGroups
   Dim i, arrGroups
   arrGroups = SelectedGroups
   If IsArray(arrGroups) Then
     For i = 0 To UBound(arrGroups)
       Rhino.Print( arrGroups(i) )
     Next
   End If
 End Sub