Package sort

▾ Example

Code:

package sort_test

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 Example() {
    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]
}

▾ Example (SortKeys)

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

Code:

package sort_test

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 Example_sortKeys() {
    // 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)

    // Output: 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)

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.

Code:

package sort_test

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 Example_sortMultiKeys() {
    // 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)

    // Output:
    // 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)

Code:

package sort_test

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 Example_sortWrapper() {
    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)

    // Output:
    // 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)
}

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

Internal call graph ▾

In the call graph viewer below, each node is a function belonging to this package and its children are the functions it calls—perhaps dynamically.

The root nodes are the entry points of the package: functions that may be called from outside the package. There may be non-exported or anonymous functions among them if they are called dynamically from another package.

Click a node to visit that function's source code. From there you can visit its callers by clicking its declaring func token.

Functions may be omitted if they were determined to be unreachable in the particular programs or tests that were analyzed.

▾ Example

Code:

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

Output:

[1 2 3 4 5 6]

▾ Example

This example demonstrates searching a list sorted in ascending order.

Code:

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)
}

Output:

found 6 at index 2 in [1 3 6 10 15 21 28 36 45 55]

▾ Example (DescendingOrder)

This example demonstrates searching a list sorted in descending order. The approach is the same as searching a list in ascending order, but with the condition inverted.

Code:

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)
}

Output:

found 6 at index 7 in [55 45 36 28 21 15 10 6 3 1]

▾ Example

Code:

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)

Output:

By name: [{Alice 55} {Bob 75} {Gopher 7} {Vera 24}]
By age: [{Gopher 7} {Vera 24} {Alice 55} {Bob 75}]

▾ Example

Code:

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

Output:

[6 5 4 3 2 1]