loopGroups.py

import clr

clr.AddReference('System')
from System.Collections.Generic import List

clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
from Autodesk.Revit.DB.Structure import *

clr.AddReference('RevitNodes')
import Revit
clr.ImportExtensions(Revit.GeometryConversion)
clr.ImportExtensions(Revit.Elements)

clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager

doc = DocumentManager.Instance.CurrentDBDocument
uidoc=DocumentManager.Instance.CurrentUIApplication.ActiveUIDocument

#allows us to loop it. we are expecting sublists in this case
def CreateGroup(items):
	for e in items:
		ids = []
		ids.append(e.Id)
		col = List[ElementId](ids)
		t = Transaction(doc,"group")
		TransactionManager.Instance.ForceCloseTransaction() #force close dynamo's auto refresh transaction
		t.Start()
		group = doc.Create.NewGroup(col)
		t.Commit()
		return group.ToDSType(True)

#our sublists
elements = UnwrapElement(IN[0])

#for output
newGroups = []
#transaction group encapsulates all the changes 
tg = TransactionGroup(doc,"OverallTransaction")
tg.Start()

for e in elements:
	newGroups.append(CreateGroup(e))
	
#now refresh
tg.Assimilate()
OUT = newGroups