[FLouvain] some refactoring

src/Data/Graph/Clustering/Example.hs

@@ -19,6 +19,7 @@ exampleRemap gr = gmap remap gr
 -- | Run FLouvain.iterate on an example graph
 -- Example call:
 -- putStrLn $ prettify $ iterateOnce cuiller
+-- Prelude.map (fst3 . unCommunity . snd) $ labNodes $ iterateOnce karate
 iterateOnce :: Gr () Double -> CGr
 iterateOnce gr = iteration fgr cgr
   where

src/Data/Graph/Clustering/FLouvain.hs

@@ -98,6 +98,8 @@ newtype Weight = Weight { unWeight :: Double }
 type FEdge b = (Weight, b)
 fedgeWeight :: FEdge b -> Double
 fedgeWeight = unWeight . fst
+sumEdgeWeights :: Adj (FEdge b) -> Double
+sumEdgeWeights es = sum $ map (fedgeWeight . fst) es
 type FGraph a b = Gr a (FEdge b)
 
 -- Used for k_i in formula (2)
@@ -143,7 +145,7 @@ type CGr = Gr Community ()
 graphWeight :: FGraph a b -> GraphWeightSum
 graphWeight gr = GraphWeightSum $ ufold weight' 0 gr
   where
-    weight' (p, _, _, s) acc = acc + sum (map (fedgeWeight . fst) $ p <> s)
+    weight' (p, _, _, s) acc = acc + (sumEdgeWeights $ p <> s)
 
 -- | Compute initial 'CGr' for a given 'FGraph a b'. This means, put each node
 -- in a separate community.
@@ -163,7 +165,7 @@ initialCGr gr = gmap singletonCom gr
         -- no internal links
         iws = InWeightSum 0.0
         -- just sum over the edges coming into/out of node v
-        tws = TotWeightSum $ sum $ map (fedgeWeight . fst) edges
+        tws = TotWeightSum $ sumEdgeWeights edges
 
 -- ALGORITHM
 
@@ -178,7 +180,7 @@ delta com ki kiin m = DeltaQ $ acc - dec
   where
     inWeightSum = comInWeightSum com
     totWeightSum = comTotWeightSum com
-    acc = accL - accR*accR
+    acc = accL - accR * accR
     accL = 0.5 * (unInWeightSum inWeightSum + 2.0 * (unNodeComWeightSum kiin)) / (unGraphWeightSum m)
     accR = 0.5 * (unTotWeightSum totWeightSum + unNodeWeightSum ki) / (unGraphWeightSum m)
     dec = decL - decM * decM - decR * decR
@@ -196,7 +198,7 @@ delta com ki kiin m = DeltaQ $ acc - dec
 -- We could avoid the higher complexity, eg. by precomputing the whole graph
 -- into a HashMap Node [Edge].
 iteration :: FGraph a b -> CGr -> CGr
-iteration gr cs = xdfsFoldWith suc' (\(_, v, _, _) -> step gw $ context gr $ v) cs (nodes gr) gr
+iteration gr cs = xdfsFoldWith suc' (\(_, v, _, _) -> step gw $ context gr  v) cs (nodes gr) gr
   where
     gw = graphWeight gr
     --weightSum = ufold weightSum' 0 gr