Overview ▹

Overview ▾

Package sort provides primitives for sorting slices and user-defined collections.

▹ Example

▾ Example

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)
	// There are two ways to sort a slice. First, one can define
	// a set of methods for the slice type, as with ByAge, and
	// call sort.Sort. In this first example we use that technique.
	sort.Sort(ByAge(people))
	fmt.Println(people)

// The other way is to use sort.Slice with a custom Less
	// function, which can be provided as a closure. In this
	// case no methods are needed. (And if they exist, they
	// are ignored.) Here we re-sort in reverse order: compare
	// the closure with ByAge.Less.
	sort.Slice(people, func(i, j int) bool {
		return people[i].Age > people[j].Age
	})
	fmt.Println(people)

}

[Bob: 31 John: 42 Michael: 17 Jenny: 26]
[Michael: 17 Jenny: 26 Bob: 31 John: 42]
[John: 42 Bob: 31 Jenny: 26 Michael: 17]

▹ Example (SortKeys)

▾ Example (SortKeys)

ExampleSortKeys demonstrates a technique for sorting a struct type using programmable sort criteria.

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(p2, p1)
	}

// 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)

}

By name: [{Earth 1 1} {Mars 0.107 1.5} {Mercury 0.055 0.4} {Venus 0.815 0.7}]
By mass: [{Mercury 0.055 0.4} {Mars 0.107 1.5} {Venus 0.815 0.7} {Earth 1 1}]
By distance: [{Mercury 0.055 0.4} {Venus 0.815 0.7} {Earth 1 1} {Mars 0.107 1.5}]
By decreasing distance: [{Mars 0.107 1.5} {Earth 1 1} {Venus 0.815 0.7} {Mercury 0.055 0.4}]

▹ Example (SortMultiKeys)

▾ Example (SortMultiKeys)

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.

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 discriminates between
// the two items (one is less than the other). 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)

}

By user: [{dmr C 100} {glenda Go 200} {gri Go 100} {gri Smalltalk 80} {ken C 150} {ken Go 200} {r Go 100} {r C 150} {rsc Go 200}]
By user,<lines: [{dmr C 100} {glenda Go 200} {gri Smalltalk 80} {gri Go 100} {ken C 150} {ken Go 200} {r Go 100} {r C 150} {rsc Go 200}]
By user,>lines: [{dmr C 100} {glenda Go 200} {gri Go 100} {gri Smalltalk 80} {ken Go 200} {ken C 150} {r C 150} {r Go 100} {rsc Go 200}]
By language,<lines: [{dmr C 100} {ken C 150} {r C 150} {r Go 100} {gri Go 100} {ken Go 200} {glenda Go 200} {rsc Go 200} {gri Smalltalk 80}]
By language,<lines,user: [{dmr C 100} {ken C 150} {r C 150} {gri Go 100} {r Go 100} {glenda Go 200} {ken Go 200} {rsc Go 200} {gri Smalltalk 80}]

▹ Example (SortWrapper)

▾ Example (SortWrapper)

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)
	}
}

Organs by weight:
prostate (62g)
pancreas (131g)
spleen   (162g)
heart    (290g)
brain    (1340g)
liver    (1494g)
Organs by name:
brain    (1340g)
heart    (290g)
liver    (1494g)
pancreas (131g)
prostate (62g)
spleen   (162g)

Package sort

Overview ▹

Overview ▾

Index ▹

Index ▾

Examples

Package files

func Float64s

func Float64sAreSorted

func Ints

func IntsAreSorted

func IsSorted

func Search

func SearchFloat64s

func SearchInts

func SearchStrings

func Slice 1.8

func SliceIsSorted 1.8

func SliceStable 1.8

func Sort

func Stable 1.2

func Strings

func StringsAreSorted

type Float64Slice

func (Float64Slice) Len

func (Float64Slice) Less

func (Float64Slice) Search

func (Float64Slice) Sort

func (Float64Slice) Swap

type IntSlice

func (IntSlice) Len

func (IntSlice) Less

func (IntSlice) Search

func (IntSlice) Sort

func (IntSlice) Swap

type Interface

func Reverse 1.1

type StringSlice

func (StringSlice) Len

func (StringSlice) Less

func (StringSlice) Search

func (StringSlice) Sort

func (StringSlice) Swap