Creating Graphs

Easy creation with extension methods

QuickGraph provides several extension methods in QuickGraph.GraphExtensions to create graph from list of edge or vertices. For example, from an IEnumerable<Edge<int>>:

usingQuickGraph;// enables extension methodsvaredges=newSEdge<int>[]{newSEdge<int>(1,2),newSEdge<int>(0,1)};vargraph=edges.ToAdjacencyGraph<int,SEdge<int>>(edges);

Create a graph instance

Let us assume we need integer vertices and edges tagged with string. Int is the vertex type and we can use the MarkedEdge generic type for the edge type:

• TVertex type: int
• TEdge type using TaggedEdge<Vertex,Marker>: TaggedEdge<int, string>

varg=newAdjacencyGraph<int,TaggedEdge<int,string>>();

Wrapping a dictionary into a graph

You may have already a dictionary on hand that represents a graph, where the keys are the vertices and the value is a collection of out-edges (or adjacent edges). You can wrap this dictionary with QuickGraph without re-allocating new memory:

Dictionary<int,int[]>dic= ...;// vertex -> target edgesvargraph=dic.ToVertexAndEdgeListGraph(
kv =>Array.ConvertAll(kv.Value, v =>newSEquatableEdge<int>(kv.Key,v)));// without extension methodsvargraph=GraphExtensions.ToVertexAndEdgeListGraph(dic,
kv =>Array.ConvertAll(kv.Value, v =>newSEquatableEdge<int>(kv.Key,v)));

Adding vertices

This snippet creates two vertices and adds them to the graph.

intv1=1;intv2=2;g.AddVertex(v1);g.AddVertex(v2);

Adding edges

The edges (v1,v2) and (v2,v1) are created and added to the graph.

vare1=newTaggedEdge<int,string>(v1,v2,”hello”);g.AddEdge(e1);

Adding edges (and vertices)

You can also add an edge and implicitely add the vertices if they are missing

// v3, v4 are not added to the graph yetvare2=newTaggedEdge<int,string>(v3,v4,”hello”);g.AddVerticesAndEdge(e2);