add averagePathLength, radius

src/IGraph/Algorithms/Structure.chs

@@ -3,8 +3,10 @@
 module IGraph.Algorithms.Structure
     ( -- * Shortest Path Related Functions
       shortestPath
+    , averagePathLength
     , diameter
     , eccentricity
+    , radius
       -- * Graph Components
     , inducedSubgraph
     , isConnected
@@ -69,6 +71,23 @@ shortestPath gr s t getEdgeW = unsafePerformIO $ allocaVector $ \path -> do
     , `Neimode'
     } -> `CInt' void- #}
 
+-- | Calculates the average shortest path length between all vertex pairs.
+averagePathLength :: Graph d v e
+                  -> EdgeType -- ^ whether to consider directed paths
+                  -> Bool     -- ^ if unconnected,
+                              -- include only connected pairs (True)
+                              -- or return number if vertices (False)
+                  -> Double
+averagePathLength graph directed unconn =
+  cFloatConv $ igraphAveragePathLength (_graph graph) directed unconn
+{-# INLINE igraphAveragePathLength #-}
+{#fun pure igraph_average_path_length as ^
+    { `IGraph'
+    , alloca- `CDouble' peek*
+    , dirToBool `EdgeType'
+    , `Bool'
+    } -> `CInt' void- #}
+
 -- | Calculates the diameter of a graph (longest geodesic).
 diameter :: Graph d v e
          -> EdgeType -- ^ whether to consider directed paths
@@ -111,6 +130,19 @@ eccentricity graph mode vids = unsafePerformIO $
     , `Neimode'
     } -> `CInt' void- #}
 
+-- | Radius of a graph.
+radius :: Graph d v e
+       -> Neimode -- ^ 'IgraphOut' to follow edges' direction,
+                  -- 'IgraphIn' to reverse it, 'IgraphAll' to ignore
+       -> Double
+radius graph mode = cFloatConv $ igraphRadius (_graph graph) mode
+{-# INLINE igraphRadius #-}
+{#fun pure igraph_radius as ^
+    { `IGraph'
+    , alloca- `CDouble' peek*
+    , `Neimode'
+    } -> `CInt' void- #}
+
 -- | Creates a subgraph induced by the specified vertices. This function collects
 -- the specified vertices and all edges between them to a new graph.
 inducedSubgraph :: (Ord v, Serialize v)

tests/Test/Algorithms.hs

@@ -21,8 +21,10 @@ tests = testGroup "Algorithms"
     [ graphIsomorphism
     , motifTest
     , cliqueTest
+    , averagePathTest
     , diameterTest
     , eccentricityTest
+    , radiusTest
     , subGraphs
     , decomposeTest
     , pagerankTest
@@ -58,6 +60,13 @@ cliqueTest = testGroup "Clique"
         [2,3,4], [2,4,5] ]
     c4 = [[1, 2, 3, 4], [1, 2, 4, 5]]
 
+averagePathTest :: TestTree
+averagePathTest = testGroup "Average path lengths"
+    [ testCase "clique" $ averagePathLength (full @'U 10 False) U True @?= 1
+    , testCase "star" $ averagePathLength (star 10) U True @?~ 1.8
+    , testCase "ring" $ averagePathLength (ring 11) U True @?= 3
+    ]
+
 diameterTest :: TestTree
 diameterTest = testGroup "Diameters"
     [ testCase "clique" $ fst (diameter (full @'U 10 False) U True)  @?= 1
@@ -75,6 +84,13 @@ eccentricityTest = testGroup "Eccentricity"
         eccentricity (ring 10) IgraphAll [0..9] @?= replicate 10 5
     ]
 
+radiusTest :: TestTree
+radiusTest = testGroup "Radius"
+    [ testCase "clique" $ radius (full @'U 10 False) IgraphAll @?= 1
+    , testCase "star" $ radius (star 10) IgraphAll @?= 1
+    , testCase "ring" $ radius (ring 10) IgraphAll @?= 5
+    ]
+
 subGraphs :: TestTree
 subGraphs = testGroup "generate induced subgraphs"
     [ testCase "" $ test case1 ]
@@ -130,3 +146,7 @@ pagerankTest = testGroup "PageRank"
     ranks = [0.47,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05]
     ranks' = map ((/100) . fromIntegral . round. (*100)) $
         pagerank gr 0.85 Nothing Nothing
+
+-- approximate equality helper
+(@?~) :: (Ord n,Fractional n) => n -> n -> Assertion
+a @?~ b = assertBool "" $ abs (b-a) < 1/65536