diff --git a/light8/util.py b/light8/util.py
--- a/light8/util.py
+++ b/light8/util.py
@@ -1,4 +1,3 @@
-
 def maxes(dicts):
     '''
     ({'a' : 5, 'b' : 9}, {'a' : 10, 'b' : 943})
@@ -14,3 +13,11 @@ def scaledict(d,scl):
     return dict([(k,v*scl) for k,v in d.items()])
     
 # class Setting that scales, maxes        
+
+def subsetdict(d, dkeys, default=0):
+    'Subset of dictionary d: only the keys in dkeys'
+    # print 'd', d, 'dkeys', dkeys
+    newd = {} # dirty variables!
+    for k in dkeys:
+        newd[k] = d.get(k, default)
+    return newd