go标准库sort之基本使用

官方抽象出来的排序接口

type Interface interface {
	// Len is the number of elements in the collection.
	Len() int
	// Less reports whether the element with
	// index i should sort before the element with index j.
	Less(i, j int) bool
	// Swap swaps the elements with indexes i and j.
	Swap(i, j int)
}

提供了对int float string三种类型的排序

使用说明在example里面有详细写到

 总结出来是四种常用的方式

1 简单的对类型的slice进行排序

2 使用比较的函数类型封装比较操作

3 支持多种比较函数

4 把需要比较的对象作为匿名对象迁移struct里面，通过struct方法进行比较

官方例子

1 使用slice进行简单排序

type Person struct {
	Name string
	Age  int
}
func (p Person) String() string {
	return fmt.Sprintf("%s: %d", p.Name, p.Age)
}
// ByAge implements sort.Interface for []Person based on
// the Age field.
type ByAge []Person
func (a ByAge) Len() int           { return len(a) }
func (a ByAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age }
func main() {
	people := []Person{
		{"Bob", 31},
		{"John", 42},
		{"Michael", 17},
		{"Jenny", 26},
	}
	fmt.Println(people)
	sort.Sort(ByAge(people))
	fmt.Println(people)
	// Output:
	// [Bob: 31 John: 42 Michael: 17 Jenny: 26]
	// [Michael: 17 Jenny: 26 Bob: 31 John: 42]
}

2 使用函数类型封装比较排序的函数

type Planet struct {
	name     string
	mass     earthMass
	distance au
}
// By is the type of a "less" function that defines the ordering of its Planet arguments.
type By func(p1, p2 *Planet) bool
// Sort is a method on the function type, By, that sorts the argument slice according to the function.
func (by By) Sort(planets []Planet) {
	ps := &planetSorter{
		planets: planets,
		by:      by, // The Sort method's receiver is the function (closure) that defines the sort order.
	}
	sort.Sort(ps)
}
// planetSorter joins a By function and a slice of Planets to be sorted.
type planetSorter struct {
	planets []Planet
	by      func(p1, p2 *Planet) bool // Closure used in the Less method.
}
// Len is part of sort.Interface.
func (s *planetSorter) Len() int {
	return len(s.planets)
}
// Swap is part of sort.Interface.
func (s *planetSorter) Swap(i, j int) {
	s.planets[i], s.planets[j] = s.planets[j], s.planets[i]
}
// Less is part of sort.Interface. It is implemented by calling the "by" closure in the sorter.
func (s *planetSorter) Less(i, j int) bool {
	return s.by(&s.planets[i], &s.planets[j])
}

　

3  支持多个比较函数

// A Change is a record of source code changes, recording user, language, and delta size.
type Change struct {
    user     string
    language string
    lines    int
}
type lessFunc func(p1, p2 *Change) bool
// multiSorter implements the Sort interface, sorting the changes within.
type multiSorter struct {
    changes []Change
    less    []lessFunc
}
// Sort sorts the argument slice according to the less functions passed to OrderedBy.
func (ms *multiSorter) Sort(changes []Change) {
    ms.changes = changes
    sort.Sort(ms)
}
// OrderedBy returns a Sorter that sorts using the less functions, in order.
// Call its Sort method to sort the data.
func OrderedBy(less ...lessFunc) *multiSorter {
    return &multiSorter{
        less: less,
    }
}
// Len is part of sort.Interface.
func (ms *multiSorter) Len() int {
    return len(ms.changes)
}
// Swap is part of sort.Interface.
func (ms *multiSorter) Swap(i, j int) {
    ms.changes[i], ms.changes[j] = ms.changes[j], ms.changes[i]
}
// Less is part of sort.Interface. It is implemented by looping along the
// less functions until it finds a comparison that is either Less or
// !Less. Note that it can call the less functions twice per call. We
// could change the functions to return -1, 0, 1 and reduce the
// number of calls for greater efficiency: an exercise for the reader.
func (ms *multiSorter) Less(i, j int) bool {
    p, q := &ms.changes[i], &ms.changes[j]
    // Try all but the last comparison.
    var k int
    for k = 0; k < len(ms.less)-1; k++ {
        less := ms.less[k]
        switch {
        case less(p, q):
            // p < q, so we have a decision.
            return true
        case less(q, p):
            // p > q, so we have a decision.
            return false
        }
        // p == q; try the next comparison.
    }
    // All comparisons to here said "equal", so just return whatever
    // the final comparison reports.
    return ms.less[k](p, q)
}

4 其实是第一种的变种

type Grams int
func (g Grams) String() string { return fmt.Sprintf("%dg", int(g)) }
type Organ struct {
    Name   string
    Weight Grams
}
type Organs []*Organ
func (s Organs) Len() int      { return len(s) }
func (s Organs) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
// ByName implements sort.Interface by providing Less and using the Len and
// Swap methods of the embedded Organs value.
type ByName struct{ Organs }
func (s ByName) Less(i, j int) bool { return s.Organs[i].Name < s.Organs[j].Name }
// ByWeight implements sort.Interface by providing Less and using the Len and
// Swap methods of the embedded Organs value.
type ByWeight struct{ Organs }
func (s ByWeight) Less(i, j int) bool { return s.Organs[i].Weight < s.Organs[j].Weight }