## DEV Community # graph: A library for creating generic graph data structures and modifying, analyzing, and visualizing them.

graph is a Go library for creating generic graph data structures and modifying, analyzing, and visualizing them.

## 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.
• Edges with optional metadata, such as weights or custom attributes.
• Visualization of graphs using the DOT language and Graphviz.
• Extensive tests with ~90% coverage, and zero dependencies.

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

## Getting started

``````go get github.com/dominikbraun/graph
``````

## Quick examples

### Create a graph of integers

``````g := graph.New(graph.IntHash)

``````

### Create a directed acyclic graph of integers

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

``````

### 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)

``````

### Create a weighted graph

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

``````

### 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())

_ = 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]
``````

### Perform a topological sort

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

// Add vertices and weighted edges ...

order, _ := graph.TopologicalSort(g)

fmt.Println(order)
``````
``````[1 2 3 4 5]
``````

### Cycle checks for acyclic graphs

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

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())

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
``````

### Setting 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.

## Concepts

### Hashes

A graph consists of nodes (or vertices) of type `T`, which are identified by a hash value of type
`K`. The hash value is obtained using the hashing function passed to `graph.New`.

### Primitive types

For primitive types such as `string` or `int`, you may use a predefined hashing function such as
`graph.IntHash` – a function that takes an integer and uses it as a hash value at the same time:

``````g := graph.New(graph.IntHash)
``````

This also means that only one vertex with a value like `5` can exist in the graph if
`graph.IntHash` used.

### Custom types

For storing custom data types, you need to provide your own hashing function. This example function
takes a `City` and returns the city name as an unique hash value:

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

Creating a graph using this hashing function will yield a graph with vertices of type `City`
identified by hash values of type `string`.

``````g := graph.New(cityHash)
``````

### Traits

The behavior of a graph, for example when adding or retrieving edges, depends on its traits. You
can set the graph's traits using the functional options provided by this library:

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

## Documentation

The full documentation is available at pkg.go.dev.