Package sort

package main

import (
	"fmt"
	"sort"
)

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)

}

package main

import (
	"fmt"
	"sort"
)

// A couple of type definitions to make the units clear.
type earthMass float64
type au float64

// A Planet defines the properties of a solar system object.
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])
}

var planets = []Planet{
	{"Mercury", 0.055, 0.4},
	{"Venus", 0.815, 0.7},
	{"Earth", 1.0, 1.0},
	{"Mars", 0.107, 1.5},
}

// ExampleSortKeys demonstrates a technique for sorting a struct type using programmable sort criteria.
func main() {
	// Closures that order the Planet structure.
	name := func(p1, p2 *Planet) bool {
		return p1.name < p2.name
	}
	mass := func(p1, p2 *Planet) bool {
		return p1.mass < p2.mass
	}
	distance := func(p1, p2 *Planet) bool {
		return p1.distance < p2.distance
	}
	decreasingDistance := func(p1, p2 *Planet) bool {
		return !distance(p1, p2)
	}

	// Sort the planets by the various criteria.
	By(name).Sort(planets)
	fmt.Println("By name:", planets)

	By(mass).Sort(planets)
	fmt.Println("By mass:", planets)

	By(distance).Sort(planets)
	fmt.Println("By distance:", planets)

	By(decreasingDistance).Sort(planets)
	fmt.Println("By decreasing distance:", planets)

}

package main

import (
	"fmt"
	"sort"
)

// 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)
}

var changes = []Change{
	{"gri", "Go", 100},
	{"ken", "C", 150},
	{"glenda", "Go", 200},
	{"rsc", "Go", 200},
	{"r", "Go", 100},
	{"ken", "Go", 200},
	{"dmr", "C", 100},
	{"r", "C", 150},
	{"gri", "Smalltalk", 80},
}

// ExampleMultiKeys demonstrates a technique for sorting a struct type using different
// sets of multiple fields in the comparison. We chain together "Less" functions, each of
// which compares a single field.
func main() {
	// Closures that order the Change structure.
	user := func(c1, c2 *Change) bool {
		return c1.user < c2.user
	}
	language := func(c1, c2 *Change) bool {
		return c1.language < c2.language
	}
	increasingLines := func(c1, c2 *Change) bool {
		return c1.lines < c2.lines
	}
	decreasingLines := func(c1, c2 *Change) bool {
		return c1.lines > c2.lines // Note: > orders downwards.
	}

	// Simple use: Sort by user.
	OrderedBy(user).Sort(changes)
	fmt.Println("By user:", changes)

	// More examples.
	OrderedBy(user, increasingLines).Sort(changes)
	fmt.Println("By user,<lines:", changes)

	OrderedBy(user, decreasingLines).Sort(changes)
	fmt.Println("By user,>lines:", changes)

	OrderedBy(language, increasingLines).Sort(changes)
	fmt.Println("By language,<lines:", changes)

	OrderedBy(language, increasingLines, user).Sort(changes)
	fmt.Println("By language,<lines,user:", changes)

}

package main

import (
	"fmt"
	"sort"
)

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 }

func main() {
	s := []*Organ{
		{"brain", 1340},
		{"heart", 290},
		{"liver", 1494},
		{"pancreas", 131},
		{"prostate", 62},
		{"spleen", 162},
	}

	sort.Sort(ByWeight{s})
	fmt.Println("Organs by weight:")
	printOrgans(s)

	sort.Sort(ByName{s})
	fmt.Println("Organs by name:")
	printOrgans(s)

}

func printOrgans(s []*Organ) {
	for _, o := range s {
		fmt.Printf("%-8s (%v)\n", o.Name, o.Weight)
	}
}

func Float64s(a []float64)

func Float64sAreSorted(a []float64) bool

func Ints(a []int)

package main

import (
	"fmt"
	"sort"
)

func main() {
	s := []int{5, 2, 6, 3, 1, 4} // unsorted
	sort.Ints(s)
	fmt.Println(s)
}

func IntsAreSorted(a []int) bool

func IsSorted(data Interface) bool

func Search(n int, f func(int) bool) int

x := 23
i := sort.Search(len(data), func(i int) bool { return data[i] >= x })
if i < len(data) && data[i] == x {
	// x is present at data[i]
} else {
	// x is not present in data,
	// but i is the index where it would be inserted.
}

func GuessingGame() {
	var s string
	fmt.Printf("Pick an integer from 0 to 100.\n")
	answer := sort.Search(100, func(i int) bool {
		fmt.Printf("Is your number <= %d? ", i)
		fmt.Scanf("%s", &s)
		return s != "" && s[0] == 'y'
	})
	fmt.Printf("Your number is %d.\n", answer)
}

package main

import (
	"fmt"
	"sort"
)

func main() {
	a := []int{1, 3, 6, 10, 15, 21, 28, 36, 45, 55}
	x := 6

	i := sort.Search(len(a), func(i int) bool { return a[i] >= x })
	if i < len(a) && a[i] == x {
		fmt.Printf("found %d at index %d in %v\n", x, i, a)
	} else {
		fmt.Printf("%d not found in %v\n", x, a)
	}
}

package main

import (
	"fmt"
	"sort"
)

func main() {
	a := []int{55, 45, 36, 28, 21, 15, 10, 6, 3, 1}
	x := 6

	i := sort.Search(len(a), func(i int) bool { return a[i] <= x })
	if i < len(a) && a[i] == x {
		fmt.Printf("found %d at index %d in %v\n", x, i, a)
	} else {
		fmt.Printf("%d not found in %v\n", x, a)
	}
}

func SearchFloat64s(a []float64, x float64) int

func SearchInts(a []int, x int) int

func SearchStrings(a []string, x string) int

func Slice(slice interface{}, less func(i, j int) bool)

package main

import (
	"fmt"
	"sort"
)

func main() {
	people := []struct {
		Name string
		Age  int
	}{
		{"Gopher", 7},
		{"Alice", 55},
		{"Vera", 24},
		{"Bob", 75},
	}
	sort.Slice(people, func(i, j int) bool { return people[i].Name < people[j].Name })
	fmt.Println("By name:", people)

	sort.Slice(people, func(i, j int) bool { return people[i].Age < people[j].Age })
	fmt.Println("By age:", people)
}

func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool

func SliceStable(slice interface{}, less func(i, j int) bool)

package main

import (
	"fmt"
	"sort"
)

func main() {

	people := []struct {
		Name string
		Age  int
	}{
		{"Alice", 25},
		{"Elizabeth", 75},
		{"Alice", 75},
		{"Bob", 75},
		{"Alice", 75},
		{"Bob", 25},
		{"Colin", 25},
		{"Elizabeth", 25},
	}

	// Sort by name, preserving original order
	sort.SliceStable(people, func(i, j int) bool { return people[i].Name < people[j].Name })
	fmt.Println("By name:", people)

	// Sort by age preserving name order
	sort.SliceStable(people, func(i, j int) bool { return people[i].Age < people[j].Age })
	fmt.Println("By age,name:", people)

}

func Sort(data Interface)

func Stable(data Interface)

func Strings(a []string)

package main

import (
	"fmt"
	"sort"
)

func main() {
	s := []string{"Go", "Bravo", "Gopher", "Alpha", "Grin", "Delta"}
	sort.Strings(s)
	fmt.Println(s)
}

func StringsAreSorted(a []string) bool

type Float64Slice []float64

func (p Float64Slice) Len() int

func (p Float64Slice) Less(i, j int) bool

func (p Float64Slice) Search(x float64) int

func (p Float64Slice) Sort()

func (p Float64Slice) Swap(i, j int)

type IntSlice []int

func (p IntSlice) Len() int

func (p IntSlice) Less(i, j int) bool

func (p IntSlice) Search(x int) int

func (p IntSlice) Sort()

func (p IntSlice) Swap(i, j int)

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)
}

func Reverse(data Interface) Interface

package main

import (
	"fmt"
	"sort"
)

func main() {
	s := []int{5, 2, 6, 3, 1, 4} // unsorted
	sort.Sort(sort.Reverse(sort.IntSlice(s)))
	fmt.Println(s)
}

type StringSlice []string

func (p StringSlice) Len() int

func (p StringSlice) Less(i, j int) bool

func (p StringSlice) Search(x string) int

func (p StringSlice) Sort()

func (p StringSlice) Swap(i, j int)