groupFinishes

import clr
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *
#The inputs to this node will be stored as a list in the IN variables.
from itertools import groupby
dataEnteringNode = IN

rooms = IN[0]
finishes=IN[1]

lst=[]
outlist =[]
for k in range(0, rooms.Count):
    lst.append([[rooms[k]]] + [finishes[k]])

for key, group in  groupby(sorted(lst, key=lambda x:x[1]), lambda x: x[1]):
    outlist.append([key] + [i[0][0] for i in group])

OUT = outlist