グラフの連結成分（エッジを列挙） ref: https://qiita.com/kkdd/items/615c19226f30e86e79d3

file0.txt

$ go run walkFrom.go
input undirected lines: [[0 1] [1 2] [2 3] [3 0] [0 2] [1 3] [1 0] [4 4] [4 4]]
total 9 lines

lineID   ! edge
----------------
2        0 [2 3]
1        1 [1 2]
5        2 [1 3]
0        3 [0 1]
6        3 [0 1]
3        4 [0 3]
4        5 [0 2]
----------------
8        6 [4 4]
7        6 [4 4]
----------------

walkFrom.go

package main

import (
    "fmt"
    "gonum.org/v1/gonum/graph"
    "gonum.org/v1/gonum/graph/multi"
    "gonum.org/v1/gonum/graph/traverse"
)

var iEdge int

func printLine(lID, mID, nID int64, iEdge int) {
    fmt.Printf("%d        %d [%d %d]\n", lID, iEdge, mID, nID)
}

func printHeader() {
    iEdge = 0
    fmt.Printf("\nlineID   ! edge\n")
    printSeparator()
}

func printSeparator() {
    fmt.Print("----------------\n")
}

func printLines(e graph.Edge) {
    mID, nID := e.From().ID(), e.To().ID()
    if mID > nID {mID, nID = nID, mID}
    l := e.(graph.Lines)
    for l.Next() {
        printLine(l.Line().ID(), mID, nID, iEdge)
    }
    iEdge++
}

func makeWalker(edgeFunc func (graph.Edge)) (walker traverse.DepthFirst) {
    walker.EdgeFilter = func(e graph.Edge) bool {
        if e.From().ID() <= e.To().ID() {
            edgeFunc(e)
        }
        return true
    }
    return walker
}

func walk(g *multi.UndirectedGraph, walker *traverse.DepthFirst, from graph.Node) {
    if !walker.Visited(from) && g.From(from.ID()).Next() {  // neither visited nor isolated node
        walker.Walk(g, from, nil)
        printSeparator()
    }
}

func walkAll(g *multi.UndirectedGraph) {
    printHeader()
    nod := g.Nodes()
    w := makeWalker(printLines)
    for nod.Next() {
        walk(g, &w, nod.Node())
    }
}

func makeGraph() *multi.UndirectedGraph {
    IDMAX := 9
    inputLines := [][]int64{{0, 1}, {1, 2}, {2, 3}, {3, 0}, {0, 2}, {1, 3},  {1, 0}, {4, 4}, {4, 4}}

    g := multi.NewUndirectedGraph()
    for i := 0; i <= IDMAX; i++ {
        g.AddNode(multi.Node(int64(i)))
    }
    fmt.Print("input undirected lines: [")
    for i, e := range inputLines {
        g.SetLine(g.NewLine(g.Node(e[0]), g.Node(e[1])))
        fmt.Print(e)
        if i < len(inputLines)-1 {fmt.Print(" ")}
    }
    fmt.Printf("]\ntotal %d lines\n", len(inputLines))
    return g
}

func main() {
    g:= makeGraph()
    walkAll(g)
}