add decompose

src/IGraph/Algorithms/Generators.chs

@@ -4,6 +4,7 @@
 module IGraph.Algorithms.Generators
     ( full
     , star
+    , ring
     , ErdosRenyiModel(..)
     , erdosRenyiGame
     , degreeSequenceGame
@@ -54,13 +55,28 @@ star n = unsafePerformIO $ do
     gr <- MGraph <$> igraphStar n IgraphStarUndirected 0
     M.initializeNullAttribute gr
     unsafeFreeze gr
-{# fun igraph_star as ^
+{#fun igraph_star as ^
     { allocaIGraph- `IGraph' addIGraphFinalizer*
     , `Int'
     , `StarMode'
     , `Int'
     } -> `CInt' void- #}
 
+-- | Creates a ring graph, a one dimensional lattice.
+ring :: Int -> Graph 'U () ()
+ring n = unsafePerformIO $ do
+    igraphInit
+    gr <- MGraph <$> igraphRing n False False True
+    M.initializeNullAttribute gr
+    unsafeFreeze gr
+{#fun igraph_ring as ^
+    { allocaIGraph- `IGraph' addIGraphFinalizer*
+    , `Int'
+    , `Bool'
+    , `Bool'
+    , `Bool'
+    } -> `CInt' void- #}
+
 data ErdosRenyiModel = GNP Int Double
                      | GNM Int Int
 

src/IGraph/Algorithms/Structure.chs

@@ -3,6 +3,7 @@ module IGraph.Algorithms.Structure
     ( -- * Shortest Path Related Functions
       getShortestPath
     , inducedSubgraph
+    , decompose
     , closeness
     , betweenness
     , eigenvectorCentrality
@@ -70,6 +71,25 @@ inducedSubgraph gr nds = unsafePerformIO $ withVerticesList nds $ \vs ->
     , `SubgraphImplementation'
     } -> `CInt' void- #}
 
+
+-- | Decompose a graph into connected components.
+decompose :: (Hashable v, Eq v, Serialize v)
+          => Graph d v e -> [Graph d v e]
+decompose gr = unsafePerformIO $ allocaVectorPtr $ \ptr -> do
+    igraphDecompose (_graph gr) ptr IgraphWeak (-1) 1
+    n <- igraphVectorPtrSize ptr
+    forM [0..n-1] $ \i -> do
+        p <- igraphVectorPtrE ptr i
+        addIGraphFinalizer (castPtr p) >>= unsafeFreeze . MGraph
+{-# INLINE decompose #-}
+{#fun igraph_decompose as ^
+    { `IGraph'
+    , castPtr `Ptr VectorPtr'
+    , `Connectedness'
+    , `Int'
+    , `Int'
+    } -> `CInt' void- #}
+
 -- | Closeness centrality
 closeness :: [Int]  -- ^ vertices
           -> Graph d v e

src/IGraph/Internal.chs

@@ -22,6 +22,9 @@ module IGraph.Internal
     , allocaVectorPtrN
     , withPtrs
     , toLists
+    , igraphVectorPtrSize
+    , igraphVectorPtrE
+    , igraphVectorPtrSet
 
       -- ** Customized bytestring for storing attributes
     , BSLen

src/IGraph/Internal/Constants.chs

@@ -24,6 +24,9 @@ module IGraph.Internal.Constants where
 {#enum igraph_subgraph_implementation_t as SubgraphImplementation {underscoreToCase}
     deriving (Show, Read, Eq) #}
 
+{#enum igraph_connectedness_t as Connectedness {underscoreToCase}
+    deriving (Eq) #}
+
 {#enum igraph_pagerank_algo_t as PagerankAlgo {underscoreToCase}
     deriving (Show, Read, Eq) #}
 

tests/Test/Algorithms.hs

@@ -20,6 +20,7 @@ tests = testGroup "Algorithms"
     , motifTest
     , cliqueTest
     , subGraphs
+    , decomposeTest
     , pagerankTest
     ]
 
@@ -66,6 +67,25 @@ subGraphs = testGroup "generate induced subgraphs"
         gr' = inducedSubgraph gr ns'
         result = map (nodeLab gr' *** nodeLab gr') $ edges gr'
 
+decomposeTest :: TestTree
+decomposeTest = testGroup "Decompose"
+    [ testCase "ring" $ edges (head $ decompose $ ring 10) @?=
+        [(0,1), (1,2), (2,3), (3,4), (4,5), (5,6), (6,7), (7,8), (8,9), (0,9)]
+    , testCase "1 component" $ do
+        gr <- erdosRenyiGame (GNP 100 (40/100)) False :: IO (Graph 'U () ())
+        1 @?= length (decompose gr)
+    , testCase "toy example" $ map (sort . edges) (decompose gr) @?=
+        [ [(0,1), (0,2), (1,2)]
+        , [(0,1), (1,2), (2,3)]
+        , []
+        , [(0,1), (1,2)] ]
+    ]
+  where
+    es = [ (0,1), (1,2), (2,0)
+		 , (3,4), (4,5), (5,6)
+		 , (8,9), (9,10) ]
+    gr = mkGraph (replicate 11 ()) $ zip es $ repeat () :: Graph 'U () ()
+
 pagerankTest :: TestTree
 pagerankTest = testGroup "PageRank"
     [ testCase "case 1" $ ranks @=? ranks' ]