added edge contractions

.config/dotnet-tools.json

@@ -4,23 +4,38 @@
   "tools": {
     "dotnet-format": {
       "version": "5.1.250801",
-      "commands": ["dotnet-format"],
+      "commands": [
+        "dotnet-format"
+      ],
       "rollForward": false
     },
     "dotnet-script": {
       "version": "1.4.0",
-      "commands": ["dotnet-script"],
+      "commands": [
+        "dotnet-script"
+      ],
       "rollForward": false
     },
     "csharpier": {
       "version": "0.29.2",
-      "commands": ["dotnet-csharpier"],
+      "commands": [
+        "dotnet-csharpier"
+      ],
       "rollForward": false
     },
     "husky": {
       "version": "0.6.1",
-      "commands": ["husky"],
+      "commands": [
+        "husky"
+      ],
+      "rollForward": false
+    },
+    "fantomas": {
+      "version": "6.3.16",
+      "commands": [
+        "fantomas"
+      ],
       "rollForward": false
     }
   }
-}
+}

SharpGraph.Builder/Compiler.fs

@@ -1,8 +1,9 @@
 namespace SharpGraph.Builder
 
-///
-///
-///
+///<summary>
+/// Compiler module to compiel expressions representing graphs into
+/// graph objects.
+///</summary>
 module Compiler =
     open SharpGraph
     open Microsoft.FSharp.Collections
@@ -121,28 +122,19 @@ module Compiler =
         | UnaryExp(e, op) -> HandleUnaryExp e op
         | BinaryOperatorExp(op, e1, e2) -> BinaryOperatorExp op e1 e2
 
-    ///
-    ///
-    ///
+
     let Parse code =
-        System.Diagnostics.Debug.WriteLine("BEGIN PARSING")
 
-        match runParserOnString (pExpression .>> eof) () "Tokamak reaction stream" code with
+        match runParserOnString (pExpression .>> eof) () "Graph compile stream" code with
         | Success(result, _, _) ->
-            System.Diagnostics.Debug.WriteLine("FINISH PARSING")
             result
         | Failure(msg, _, _) ->
-            System.Diagnostics.Debug.WriteLine("Error  " + msg + "Reactor core containment failed!")
             failwith msg
 
+    ///<summary>
+    /// Compiles the given string into a Graph object.
+    ///</summary>
+    ///<param name="code">The input string to build the graph</param>
+    ///<returns>Graph object</returns>
     let Compile (text: string) =
-        let result = HandleExpression(Parse text)
-
-        System.Console.WriteLine(
-            "graph number of nodes "
-            + string (result.GetNodes().Count)
-            + " and edges: "
-            + string (result.GetEdges().Count)
-        )
-
-        result
+        HandleExpression(Parse text)

SharpGraph.Builder/SharpGraph.Builder.fsproj

@@ -3,7 +3,7 @@
     <PackageId>SharpGraphLib.Builder</PackageId>
     <TargetFramework>net8.0</TargetFramework> 
     <PackageReadmeFile>README.md</PackageReadmeFile>
-    <Version>1.0.3</Version>
+    <Version>1.0.4</Version>
     <Authors>Jonathan Hough</Authors>
     <Company>Jonathan Hough</Company>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>

SharpGraph.Tests/test/CycleTest.cs

@@ -3,13 +3,6 @@
 // Copyright Licensed under the MIT license.
 // See LICENSE file in the samples root for full license information.
 // </copyright>
-
-using System;
-// <copyright file="CycleTest.cs" company="Jonathan Hough">
-// Copyright (C) 2023 Jonathan Hough.
-// Copyright Licensed under the MIT license.
-// See LICENSE file in the samples root for full license information.
-// </copyright>
 using Xunit;
 
 namespace SharpGraph

SharpGraph.Tests/test/GraphContractionTest.cs

@@ -0,0 +1,60 @@
+// <copyright file="GraphContractionTest.cs" company="Jonathan Hough">
+// Copyright (C) 2023 Jonathan Hough.
+// Copyright Licensed under the MIT license.
+// See LICENSE file in the samples root for full license information.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+using Xunit;
+
+namespace SharpGraph
+{
+    public class GraphContractionTest
+    {
+        [Theory]
+        [InlineData(6, "1", "2", 5, 10, 4)]
+        [InlineData(10, "2", "6", 9, 36, 8)]
+        public void TestContractEdgeFromComplete(
+            uint totalNodeCount,
+            string nodeToKeep,
+            string nodeToRemove,
+            int expectedNumberOfNodes,
+            int expectedNumberOfEdges,
+            int expectedAdjacentToKeptNode
+        )
+        {
+            var edgeToRemove = new Edge(nodeToKeep, nodeToRemove);
+            var g = GraphGenerator.CreateComplete(totalNodeCount);
+            var h = g.ContractEdge(edgeToRemove, new Node(nodeToKeep));
+
+            Assert.Equal(expectedNumberOfNodes, h.GetNodes().Count);
+            Assert.Equal(expectedNumberOfEdges, h.GetEdges().Count);
+            Assert.Equal(expectedAdjacentToKeptNode, h.GetAdjacent(new Node(nodeToKeep)).Count);
+        }
+
+        [Fact]
+        public void TestContractionKeepsComponents()
+        {
+            var e1 = new Edge("1", "2");
+            var e2 = new Edge("2", "3");
+            var e3 = new Edge("2", "4");
+            var e4 = new Edge("5", "8");
+            var edges = new List<Edge> { e1, e2, e3, e4 };
+            var g = new Graph(edges);
+            foreach (var e in g.GetEdges())
+            {
+                g.AddComponent<EdgeDirection>(e);
+            }
+
+            var h = g.ContractEdge(e1, new Node("1"));
+
+            Assert.Equal(5, h.GetNodes().Count);
+            Assert.Equal(3, h.GetEdges().Count);
+            Assert.Equal(2, h.GetAdjacent(new Node("1")).Count);
+
+            // edge that was not updated should have kept the component
+            Assert.True(h.HasComponent<EdgeDirection>(e4));
+        }
+    }
+}

SharpGraph/SharpGraph.csproj

@@ -4,7 +4,7 @@
     <TargetFramework>net8.0</TargetFramework>
     <PackageId>SharpGraphLib</PackageId>
     <PackageReadmeFile>README.md</PackageReadmeFile>
-    <Version>1.0.3</Version>
+    <Version>1.0.4</Version>
     <Authors>Jonathan Hough</Authors>
     <Company>Jonathan Hough</Company>
   </PropertyGroup>

SharpGraph/src/core/Graph.Contraction.cs

@@ -0,0 +1,84 @@
+// <copyright file="Graph.Contraction.cs" company="Jonathan Hough">
+// Copyright (C) 2023 Jonathan Hough.
+// Copyright Licensed under the MIT license.
+// See LICENSE file in the samples root for full license information.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+
+namespace SharpGraph
+{
+    public partial class Graph
+    {
+        /// <summary>
+        /// Contracts the edge from the graph. This essentially removes the edge form the graph.
+        /// Incident edges will be reassigned to connect to the "keep"  node, which is one of the
+        /// two nodes of the to-be-deleted edge.
+        /// Edges that previously connected to the to-be-deleted node, will be deleted, and new edges to
+        /// the to-be-kept node will be created.
+        /// For edges not incident with the edge that is to be deleted, the edges in the returned graph will
+        /// be copies, including any components.
+        /// </summary>
+        /// <param name="edge">Edge to be deleted.</param>
+        /// <param name="keep">Node of deleted edge to keep in output graph.</param>
+        /// <returns>Graph with edge removed.</returns>
+        public Graph ContractEdge(Edge edge, Node keep)
+        {
+            if (this.GetEdges().Contains(edge) == false)
+            {
+                throw new Exception("Edge does not exist on this graph.");
+            }
+
+            if (!edge.Nodes().Contains(keep))
+            {
+                throw new Exception(
+                    "Node to keep does not exist in the edge ot remove. Cannot remove edge."
+                );
+            }
+
+            var removeNode = keep == edge.To() ? edge.From() : edge.To();
+            var incident = this.GetIncidentEdges(removeNode);
+            var toRemove = new HashSet<Edge>();
+            var newEdges = new HashSet<Edge>();
+            toRemove.Add(edge);
+            foreach (var e in incident)
+            {
+                if (toRemove.Contains(e))
+                {
+                    continue;
+                }
+
+                if (!e.Nodes().Contains(keep))
+                {
+                    if (removeNode == e.To())
+                    {
+                        toRemove.Add(e);
+                        var rex = new Edge(keep, e.From());
+                        newEdges.Add(rex);
+                    }
+                    else if (removeNode == e.From())
+                    {
+                        toRemove.Add(e);
+                        var rex = new Edge(keep, e.To());
+                        newEdges.Add(rex);
+                    }
+                }
+            }
+
+            var g = this.Copy();
+            foreach (var deadEdge in toRemove)
+            {
+                g.RemoveEdge(deadEdge);
+            }
+
+            g.RemoveNode(removeNode);
+            foreach (var newEdge in newEdges)
+            {
+                g.AddEdge(newEdge);
+            }
+
+            return g;
+        }
+    }
+}

SharpGraph/src/core/Graph.cs

@@ -353,7 +353,7 @@ public bool RemoveNode(Node node)
             if (incidentEdges != null)
             {
                 this.edges.RemoveAll(e => incidentEdges.Contains(e));
-                incidentEdges.RemoveWhere(e => incidentEdges.Contains(e));
+                incidentEdges.RemoveWhere(e => e.Equals(e));
             }
 
             this.nodes.Remove(node);
@@ -407,13 +407,13 @@ public bool RemoveEdge(Edge edge)
             var fromIncidentEdges = this.incidenceMap[f];
             if (fromIncidentEdges != null)
             {
-                fromIncidentEdges.RemoveWhere(e => e.Equals(edge));
+                int i = fromIncidentEdges.RemoveWhere(e => e.Equals(edge));
             }
 
             var toIncidentEdges = this.incidenceMap[t];
             if (toIncidentEdges != null)
             {
-                toIncidentEdges.RemoveWhere(e => e.Equals(edge));
+                int i = toIncidentEdges.RemoveWhere(e => e.Equals(edge));
             }
 
             this.edgeComponents.Remove(edge);

SharpGraphProj.code-workspace

@@ -4,5 +4,9 @@
 			"path": "."
 		}
 	],
-	"settings": {}
+	"settings": {
+		"files.associations": {
+			".fantomasignore": "ignore" 
+		}
+	}
 }