Creating Graphs - KeRNeLith/QuikGraph GitHub Wiki

Creating Graphs

Easy creation with extension methods

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

using QuikGraph; // enables extension methods

var edges = new[] { new Edge<int>(1, 2), new Edge<int>(0,1) };
var graph = edges.ToAdjacencyGraph<int, Edge<int>>();

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 TaggedEdge<TVertex, TTag> generic type for the edge type:

  • TVertex is int
  • TEdge type using TaggedEdge<Vertex, Marker>: TaggedEdge<int, string> 
var graph = new AdjacencyGraph<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 QuikGraph without re-allocating new memory:

Dictionary<int, int[]> dictionary = ...; // Vertex -> Target edges
var graph = dictionary.ToDelegateVertexAndEdgeListGraph(
    kv => Array.ConvertAll(kv.Value, v => new Edge<int>(kv.Key, v)));

// Without extension method
var graph = GraphExtensions.ToDelegateVertexAndEdgeListGraph(
    dictionary,
    kv => Array.ConvertAll(kv.Value, v => new Edge<int>(kv.Key, v)));

Adding vertices

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

int vertex1 = 1;
int vertex2 = 2;

graph.AddVertex(vertex1);
graph.AddVertex(vertex2);

Adding edges

Adds an edge to the graph. Note that vertices vertex1 and vertex2 are already added to the graph beforehand.

var edge1 = new TaggedEdge<int, string>(vertex1, vertex2, "hello");

graph.AddEdge(edge1);

For more details about QuikGraph built-in edge objects you can consult the Edges page.

Adding edges (and vertices)

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

// vertex3, vertex4 are not added into the graph yet
var edge2 = new TaggedEdge<int, string>(vertex3, vertex4, "hello");

graph.AddVerticesAndEdge(edge2);

Vertex and edge ranges

It is also possible to add a batch of vertices (same for edges) in one operation.

// Vertex range
graph.AddVertexRange(new[] { vertex5, vertex6 });

// Edge range
graph.AddEdgeRange(new[] { edge3, edge4 });

// Edge range (and implicitly vertices)
graph.AddVerticesAndEdgeRange(new[] { edge5, edge6 });
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