A library for creating generic graph data structures and modifying, analyzing, and visualizing them.

Are you using graph? Check out the graph user survey.

Features

Generic vertices of any type, such as int or City.
Graph traits with corresponding validations, such as cycle checks in acyclic graphs.
Algorithms for finding paths or components, such as shortest paths or strongly connected components.
Algorithms for transformations and representations, such as transitive reduction or topological order.
Algorithms for non-recursive graph traversal, such as DFS or BFS.
Vertices and edges with optional metadata, such as weights or custom attributes.
Visualization of graphs using the DOT language and Graphviz.
Integrate any storage backend by using your own Store implementation.
Extensive tests with ~90% coverage, and zero dependencies.

Status: Because graph is in version 0, the public API shouldn't be considered stable.

This README may contain unreleased changes. Check out the latest documentation.

Getting started

go get github.com/dominikbraun/graph

Quick examples

Create a graph of integers

g := graph.New(graph.IntHash)

_ = g.AddVertex(1)
_ = g.AddVertex(2)
_ = g.AddVertex(3)
_ = g.AddVertex(4)
_ = g.AddVertex(5)

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 4)
_ = g.AddEdge(2, 3)
_ = g.AddEdge(2, 4)
_ = g.AddEdge(2, 5)
_ = g.AddEdge(3, 5)

Create a directed acyclic graph of integers

g := graph.New(graph.IntHash, graph.Directed(), graph.Acyclic())

_ = g.AddVertex(1)
_ = g.AddVertex(2)
_ = g.AddVertex(3)
_ = g.AddVertex(4)

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)
_ = g.AddEdge(2, 3)
_ = g.AddEdge(2, 4)
_ = g.AddEdge(3, 4)

Create a graph of a custom type

To understand this example in detail, see the concept of hashes.

type City struct {
    Name string
}

cityHash := func(c City) string {
    return c.Name
}

g := graph.New(cityHash)

_ = g.AddVertex(london)

Create a weighted graph

g := graph.New(cityHash, graph.Weighted())

_ = g.AddVertex(london)
_ = g.AddVertex(munich)
_ = g.AddVertex(paris)
_ = g.AddVertex(madrid)

_ = g.AddEdge("london", "munich", graph.EdgeWeight(3))
_ = g.AddEdge("london", "paris", graph.EdgeWeight(2))
_ = g.AddEdge("london", "madrid", graph.EdgeWeight(5))
_ = g.AddEdge("munich", "madrid", graph.EdgeWeight(6))
_ = g.AddEdge("munich", "paris", graph.EdgeWeight(2))
_ = g.AddEdge("paris", "madrid", graph.EdgeWeight(4))

Perform a Depth-First Search

This example traverses and prints all vertices in the graph in DFS order.

g := graph.New(graph.IntHash, graph.Directed())

_ = g.AddVertex(1)
_ = g.AddVertex(2)
_ = g.AddVertex(3)
_ = g.AddVertex(4)

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)
_ = g.AddEdge(3, 4)

_ = graph.DFS(g, 1, func(value int) bool {
    fmt.Println(value)
    return false
})

1 3 4 2

Find strongly connected components

g := graph.New(graph.IntHash)

// Add vertices and edges ...

scc, _ := graph.StronglyConnectedComponents(g)

fmt.Println(scc)

[[1 2 5] [3 4 8] [6 7]]

Find the shortest path

g := graph.New(graph.StringHash, graph.Weighted())

// Add vertices and weighted edges ...

path, _ := graph.ShortestPath(g, "A", "B")

fmt.Println(path)

[A C E B]

Find spanning trees

g := graph.New(graph.StringHash, graph.Weighted())

// Add vertices and edges ...

mst, _ := graph.MinimumSpanningTree(g)

Perform a topological sort

g := graph.New(graph.IntHash, graph.Directed(), graph.PreventCycles())

// Add vertices and edges ...

// For a deterministic topological ordering, use StableTopologicalSort.
order, _ := graph.TopologicalSort(g)

fmt.Println(order)

[1 2 3 4 5]

Perform a transitive reduction

g := graph.New(graph.StringHash, graph.Directed(), graph.PreventCycles())

// Add vertices and edges ...

transitiveReduction, _ := graph.TransitiveReduction(g)

Prevent the creation of cycles

g := graph.New(graph.IntHash, graph.PreventCycles())

_ = g.AddVertex(1)
_ = g.AddVertex(2)
_ = g.AddVertex(3)

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)

if err := g.AddEdge(2, 3); err != nil {
    panic(err)
}

panic: an edge between 2 and 3 would introduce a cycle

Visualize a graph using Graphviz

The following example will generate a DOT description for g and write it into the given file.

g := graph.New(graph.IntHash, graph.Directed())

_ = g.AddVertex(1)
_ = g.AddVertex(2)
_ = g.AddVertex(3)

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)

file, _ := os.Create("./mygraph.gv")
_ = draw.DOT(g, file)

To generate an SVG from the created file using Graphviz, use a command such as the following:

dot -Tsvg -O mygraph.gv

The DOT function also supports rendering graph attributes:

_ = draw.DOT(g, file, draw.GraphAttribute("label", "my-graph"))

Draw a graph as in this documentation

This graph has been rendered using the following program:

package main

import (
	"os"

	"github.com/dominikbraun/graph"
	"github.com/dominikbraun/graph/draw"
)

func main() {
	g := graph.New(graph.IntHash)

	_ = g.AddVertex(1, graph.VertexAttribute("colorscheme", "blues3"), graph.VertexAttribute("style", "filled"), graph.VertexAttribute("color", "2"), graph.VertexAttribute("fillcolor", "1"))
	_ = g.AddVertex(2, graph.VertexAttribute("colorscheme", "greens3"), graph.VertexAttribute("style", "filled"), graph.VertexAttribute("color", "2"), graph.VertexAttribute("fillcolor", "1"))
	_ = g.AddVertex(3, graph.VertexAttribute("colorscheme", "purples3"), graph.VertexAttribute("style", "filled"), graph.VertexAttribute("color", "2"), graph.VertexAttribute("fillcolor", "1"))
	_ = g.AddVertex(4, graph.VertexAttribute("colorscheme", "ylorbr3"), graph.VertexAttribute("style", "filled"), graph.VertexAttribute("color", "2"), graph.VertexAttribute("fillcolor", "1"))
	_ = g.AddVertex(5, graph.VertexAttribute("colorscheme", "reds3"), graph.VertexAttribute("style", "filled"), graph.VertexAttribute("color", "2"), graph.VertexAttribute("fillcolor", "1"))

	_ = g.AddEdge(1, 2)
	_ = g.AddEdge(1, 4)
	_ = g.AddEdge(2, 3)
	_ = g.AddEdge(2, 4)
	_ = g.AddEdge(2, 5)
	_ = g.AddEdge(3, 5)

	file, _ := os.Create("./simple.gv")
	_ = draw.DOT(g, file)
}

It has been rendered using the neato engine:

dot -Tsvg -Kneato -O simple.gv

The example uses the Brewer color scheme supported by Graphviz.

Storing edge attributes

Edges may have one or more attributes which can be used to store metadata. Attributes will be taken into account when visualizing a graph. For example, this edge will be rendered in red color:

_ = g.AddEdge(1, 2, graph.EdgeAttribute("color", "red"))

To get an overview of all supported attributes, take a look at the DOT documentation.

The stored attributes can be retrieved by getting the edge and accessing the Properties.Attributes field.

edge, _ := g.Edge(1, 2)
color := edge.Properties.Attributes["color"]

Storing edge data

It is also possible to store arbitrary data inside edges, not just key-value string pairs. This data is of type any.

_  = g.AddEdge(1, 2, graph.EdgeData(myData))

The stored data can be retrieved by getting the edge and accessing the Properties.Data field.

edge, _ := g.Edge(1, 2)
myData := edge.Properties.Data

Updating edge data

Edge properties can be updated using Graph.UpdateEdge. The following example adds a new color attribute to the edge (A,B) and sets the edge weight to 10.

_ = g.UpdateEdge("A", "B", graph.EdgeAttribute("color", "red"), graph.EdgeWeight(10))

The method signature and the accepted functional options are exactly the same as for Graph.AddEdge.

Storing vertex attributes

Vertices may have one or more attributes which can be used to store metadata. Attributes will be taken into account when visualizing a graph. For example, this vertex will be rendered in red color:

_ = g.AddVertex(1, graph.VertexAttribute("style", "filled"))

The stored data can be retrieved by getting the vertex using VertexWithProperties and accessing the Attributes field.

vertex, properties, _ := g.VertexWithProperties(1)
style := properties.Attributes["style"]