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diff --git a/devdocs/go/sort%2Findex.html b/devdocs/go/sort%2Findex.html new file mode 100644 index 00000000..3e37b155 --- /dev/null +++ b/devdocs/go/sort%2Findex.html @@ -0,0 +1,648 @@ +<h1> Package sort </h1> <ul id="short-nav"> +<li><code>import "sort"</code></li> +<li><a href="#pkg-overview" class="overviewLink">Overview</a></li> +<li><a href="#pkg-index" class="indexLink">Index</a></li> +<li><a href="#pkg-examples" class="examplesLink">Examples</a></li> +</ul> <h2 id="pkg-overview">Overview </h2> <p>Package sort provides primitives for sorting slices and user-defined collections. </p> <h4 id="example_"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">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) + // 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) + + // Output: + // [Bob: 31 John: 42 Michael: 17 Jenny: 26] + // [Michael: 17 Jenny: 26 Bob: 31 John: 42] + // [John: 42 Bob: 31 Jenny: 26 Michael: 17] +} +</pre> <h4 id="example__sortKeys"> <span class="text">Example (SortKeys)</span> +</h4> <p>ExampleSortKeys demonstrates a technique for sorting a struct type using programmable sort criteria. </p> <p>Code:</p> <pre class="code" data-language="go">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(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) + + // 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}] +} +</pre> <h4 id="example__sortMultiKeys"> <span class="text">Example (SortMultiKeys)</span> +</h4> <p>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. </p> <p>Code:</p> <pre class="code" data-language="go">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 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 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} {gri Go 100} {r Go 100} {glenda Go 200} {ken 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}] + +} +</pre> <h4 id="example__sortWrapper"> <span class="text">Example (SortWrapper)</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">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) + } +} +</pre> <h2 id="pkg-index">Index </h2> <ul id="manual-nav"> +<li><a href="#Find">func Find(n int, cmp func(int) int) (i int, found bool)</a></li> +<li><a href="#Float64s">func Float64s(x []float64)</a></li> +<li><a href="#Float64sAreSorted">func Float64sAreSorted(x []float64) bool</a></li> +<li><a href="#Ints">func Ints(x []int)</a></li> +<li><a href="#IntsAreSorted">func IntsAreSorted(x []int) bool</a></li> +<li><a href="#IsSorted">func IsSorted(data Interface) bool</a></li> +<li><a href="#Search">func Search(n int, f func(int) bool) int</a></li> +<li><a href="#SearchFloat64s">func SearchFloat64s(a []float64, x float64) int</a></li> +<li><a href="#SearchInts">func SearchInts(a []int, x int) int</a></li> +<li><a href="#SearchStrings">func SearchStrings(a []string, x string) int</a></li> +<li><a href="#Slice">func Slice(x any, less func(i, j int) bool)</a></li> +<li><a href="#SliceIsSorted">func SliceIsSorted(x any, less func(i, j int) bool) bool</a></li> +<li><a href="#SliceStable">func SliceStable(x any, less func(i, j int) bool)</a></li> +<li><a href="#Sort">func Sort(data Interface)</a></li> +<li><a href="#Stable">func Stable(data Interface)</a></li> +<li><a href="#Strings">func Strings(x []string)</a></li> +<li><a href="#StringsAreSorted">func StringsAreSorted(x []string) bool</a></li> +<li><a href="#Float64Slice">type Float64Slice</a></li> +<li> <a href="#Float64Slice.Len">func (x Float64Slice) Len() int</a> +</li> +<li> <a href="#Float64Slice.Less">func (x Float64Slice) Less(i, j int) bool</a> +</li> +<li> <a href="#Float64Slice.Search">func (p Float64Slice) Search(x float64) int</a> +</li> +<li> <a href="#Float64Slice.Sort">func (x Float64Slice) Sort()</a> +</li> +<li> <a href="#Float64Slice.Swap">func (x Float64Slice) Swap(i, j int)</a> +</li> +<li><a href="#IntSlice">type IntSlice</a></li> +<li> <a href="#IntSlice.Len">func (x IntSlice) Len() int</a> +</li> +<li> <a href="#IntSlice.Less">func (x IntSlice) Less(i, j int) bool</a> +</li> +<li> <a href="#IntSlice.Search">func (p IntSlice) Search(x int) int</a> +</li> +<li> <a href="#IntSlice.Sort">func (x IntSlice) Sort()</a> +</li> +<li> <a href="#IntSlice.Swap">func (x IntSlice) Swap(i, j int)</a> +</li> +<li><a href="#Interface">type Interface</a></li> +<li> <a href="#Reverse">func Reverse(data Interface) Interface</a> +</li> +<li><a href="#StringSlice">type StringSlice</a></li> +<li> <a href="#StringSlice.Len">func (x StringSlice) Len() int</a> +</li> +<li> <a href="#StringSlice.Less">func (x StringSlice) Less(i, j int) bool</a> +</li> +<li> <a href="#StringSlice.Search">func (p StringSlice) Search(x string) int</a> +</li> +<li> <a href="#StringSlice.Sort">func (x StringSlice) Sort()</a> +</li> +<li> <a href="#StringSlice.Swap">func (x StringSlice) Swap(i, j int)</a> +</li> +</ul> <div id="pkg-examples"> <h3>Examples</h3> <dl> <dd><a class="exampleLink" href="#example_">Package</a></dd> <dd><a class="exampleLink" href="#example_Float64s">Float64s</a></dd> <dd><a class="exampleLink" href="#example_Float64sAreSorted">Float64sAreSorted</a></dd> <dd><a class="exampleLink" href="#example_Ints">Ints</a></dd> <dd><a class="exampleLink" href="#example_IntsAreSorted">IntsAreSorted</a></dd> <dd><a class="exampleLink" href="#example_Reverse">Reverse</a></dd> <dd><a class="exampleLink" href="#example_Search">Search</a></dd> <dd><a class="exampleLink" href="#example_SearchFloat64s">SearchFloat64s</a></dd> <dd><a class="exampleLink" href="#example_SearchInts">SearchInts</a></dd> <dd><a class="exampleLink" href="#example_Search_descendingOrder">Search (DescendingOrder)</a></dd> <dd><a class="exampleLink" href="#example_Slice">Slice</a></dd> <dd><a class="exampleLink" href="#example_SliceStable">SliceStable</a></dd> <dd><a class="exampleLink" href="#example_Strings">Strings</a></dd> <dd><a class="exampleLink" href="#example__sortKeys">Package (SortKeys)</a></dd> <dd><a class="exampleLink" href="#example__sortMultiKeys">Package (SortMultiKeys)</a></dd> <dd><a class="exampleLink" href="#example__sortWrapper">Package (SortWrapper)</a></dd> </dl> </div> <h3>Package files</h3> <p> <span>search.go</span> <span>slice.go</span> <span>sort.go</span> <span>sort_impl_go121.go</span> <span>zsortfunc.go</span> <span>zsortinterface.go</span> </p> <h2 id="Find">func <span>Find</span> <span title="Added in Go 1.19">1.19</span> </h2> <pre data-language="go">func Find(n int, cmp func(int) int) (i int, found bool)</pre> <p>Find uses binary search to find and return the smallest index i in [0, n) at which cmp(i) <= 0. If there is no such index i, Find returns i = n. The found result is true if i < n and cmp(i) == 0. Find calls cmp(i) only for i in the range [0, n). </p> +<p>To permit binary search, Find requires that cmp(i) > 0 for a leading prefix of the range, cmp(i) == 0 in the middle, and cmp(i) < 0 for the final suffix of the range. (Each subrange could be empty.) The usual way to establish this condition is to interpret cmp(i) as a comparison of a desired target value t against entry i in an underlying indexed data structure x, returning <0, 0, and >0 when t < x[i], t == x[i], and t > x[i], respectively. </p> +<p>For example, to look for a particular string in a sorted, random-access list of strings: </p> +<pre data-language="go">i, found := sort.Find(x.Len(), func(i int) int { + return strings.Compare(target, x.At(i)) +}) +if found { + fmt.Printf("found %s at entry %d\n", target, i) +} else { + fmt.Printf("%s not found, would insert at %d", target, i) +} +</pre> <h2 id="Float64s">func <span>Float64s</span> </h2> <pre data-language="go">func Float64s(x []float64)</pre> <p>Float64s sorts a slice of float64s in increasing order. Not-a-number (NaN) values are ordered before other values. </p> +<p>Note: as of Go 1.22, this function simply calls <span>slices.Sort</span>. </p> <h4 id="example_Float64s"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">s := []float64{5.2, -1.3, 0.7, -3.8, 2.6} // unsorted +sort.Float64s(s) +fmt.Println(s) + +s = []float64{math.Inf(1), math.NaN(), math.Inf(-1), 0.0} // unsorted +sort.Float64s(s) +fmt.Println(s) + +</pre> <p>Output:</p> <pre class="output" data-language="go">[-3.8 -1.3 0.7 2.6 5.2] +[NaN -Inf 0 +Inf] +</pre> <h2 id="Float64sAreSorted">func <span>Float64sAreSorted</span> </h2> <pre data-language="go">func Float64sAreSorted(x []float64) bool</pre> <p>Float64sAreSorted reports whether the slice x is sorted in increasing order, with not-a-number (NaN) values before any other values. </p> +<p>Note: as of Go 1.22, this function simply calls <span>slices.IsSorted</span>. </p> <h4 id="example_Float64sAreSorted"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">s := []float64{0.7, 1.3, 2.6, 3.8, 5.2} // sorted ascending +fmt.Println(sort.Float64sAreSorted(s)) + +s = []float64{5.2, 3.8, 2.6, 1.3, 0.7} // sorted descending +fmt.Println(sort.Float64sAreSorted(s)) + +s = []float64{5.2, 1.3, 0.7, 3.8, 2.6} // unsorted +fmt.Println(sort.Float64sAreSorted(s)) + +</pre> <p>Output:</p> <pre class="output" data-language="go">true +false +false +</pre> <h2 id="Ints">func <span>Ints</span> </h2> <pre data-language="go">func Ints(x []int)</pre> <p>Ints sorts a slice of ints in increasing order. </p> +<p>Note: as of Go 1.22, this function simply calls <span>slices.Sort</span>. </p> <h4 id="example_Ints"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">s := []int{5, 2, 6, 3, 1, 4} // unsorted +sort.Ints(s) +fmt.Println(s) +</pre> <p>Output:</p> <pre class="output" data-language="go">[1 2 3 4 5 6] +</pre> <h2 id="IntsAreSorted">func <span>IntsAreSorted</span> </h2> <pre data-language="go">func IntsAreSorted(x []int) bool</pre> <p>IntsAreSorted reports whether the slice x is sorted in increasing order. </p> +<p>Note: as of Go 1.22, this function simply calls <span>slices.IsSorted</span>. </p> <h4 id="example_IntsAreSorted"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">s := []int{1, 2, 3, 4, 5, 6} // sorted ascending +fmt.Println(sort.IntsAreSorted(s)) + +s = []int{6, 5, 4, 3, 2, 1} // sorted descending +fmt.Println(sort.IntsAreSorted(s)) + +s = []int{3, 2, 4, 1, 5} // unsorted +fmt.Println(sort.IntsAreSorted(s)) + +</pre> <p>Output:</p> <pre class="output" data-language="go">true +false +false +</pre> <h2 id="IsSorted">func <span>IsSorted</span> </h2> <pre data-language="go">func IsSorted(data Interface) bool</pre> <p>IsSorted reports whether data is sorted. </p> +<p>Note: in many situations, the newer <span>slices.IsSortedFunc</span> function is more ergonomic and runs faster. </p> +<h2 id="Search">func <span>Search</span> </h2> <pre data-language="go">func Search(n int, f func(int) bool) int</pre> <p>Search uses binary search to find and return the smallest index i in [0, n) at which f(i) is true, assuming that on the range [0, n), f(i) == true implies f(i+1) == true. That is, Search requires that f is false for some (possibly empty) prefix of the input range [0, n) and then true for the (possibly empty) remainder; Search returns the first true index. If there is no such index, Search returns n. (Note that the "not found" return value is not -1 as in, for instance, strings.Index.) Search calls f(i) only for i in the range [0, n). </p> +<p>A common use of Search is to find the index i for a value x in a sorted, indexable data structure such as an array or slice. In this case, the argument f, typically a closure, captures the value to be searched for, and how the data structure is indexed and ordered. </p> +<p>For instance, given a slice data sorted in ascending order, the call Search(len(data), func(i int) bool { return data[i] >= 23 }) returns the smallest index i such that data[i] >= 23. If the caller wants to find whether 23 is in the slice, it must test data[i] == 23 separately. </p> +<p>Searching data sorted in descending order would use the <= operator instead of the >= operator. </p> +<p>To complete the example above, the following code tries to find the value x in an integer slice data sorted in ascending order: </p> +<pre data-language="go">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. +} +</pre> <p>As a more whimsical example, this program guesses your number: </p> +<pre data-language="go">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) +} +</pre> <h4 id="example_Search"> <span class="text">Example</span> +</h4> <p>This example demonstrates searching a list sorted in ascending order. </p> <p>Code:</p> <pre class="code" data-language="go">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) +} +</pre> <p>Output:</p> <pre class="output" data-language="go">found 6 at index 2 in [1 3 6 10 15 21 28 36 45 55] +</pre> <h4 id="example_Search_descendingOrder"> <span class="text">Example (DescendingOrder)</span> +</h4> <p>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. </p> <p>Code:</p> <pre class="code" data-language="go">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) +} +</pre> <p>Output:</p> <pre class="output" data-language="go">found 6 at index 7 in [55 45 36 28 21 15 10 6 3 1] +</pre> <h2 id="SearchFloat64s">func <span>SearchFloat64s</span> </h2> <pre data-language="go">func SearchFloat64s(a []float64, x float64) int</pre> <p>SearchFloat64s searches for x in a sorted slice of float64s and returns the index as specified by <a href="#Search">Search</a>. The return value is the index to insert x if x is not present (it could be len(a)). The slice must be sorted in ascending order. </p> <h4 id="example_SearchFloat64s"> <span class="text">Example</span> +</h4> <p>This example demonstrates searching for float64 in a list sorted in ascending order. </p> <p>Code:</p> <pre class="code" data-language="go">a := []float64{1.0, 2.0, 3.3, 4.6, 6.1, 7.2, 8.0} + +x := 2.0 +i := sort.SearchFloat64s(a, x) +fmt.Printf("found %g at index %d in %v\n", x, i, a) + +x = 0.5 +i = sort.SearchFloat64s(a, x) +fmt.Printf("%g not found, can be inserted at index %d in %v\n", x, i, a) +</pre> <p>Output:</p> <pre class="output" data-language="go">found 2 at index 1 in [1 2 3.3 4.6 6.1 7.2 8] +0.5 not found, can be inserted at index 0 in [1 2 3.3 4.6 6.1 7.2 8] +</pre> <h2 id="SearchInts">func <span>SearchInts</span> </h2> <pre data-language="go">func SearchInts(a []int, x int) int</pre> <p>SearchInts searches for x in a sorted slice of ints and returns the index as specified by <a href="#Search">Search</a>. The return value is the index to insert x if x is not present (it could be len(a)). The slice must be sorted in ascending order. </p> <h4 id="example_SearchInts"> <span class="text">Example</span> +</h4> <p>This example demonstrates searching for int in a list sorted in ascending order. </p> <p>Code:</p> <pre class="code" data-language="go">a := []int{1, 2, 3, 4, 6, 7, 8} + +x := 2 +i := sort.SearchInts(a, x) +fmt.Printf("found %d at index %d in %v\n", x, i, a) + +x = 5 +i = sort.SearchInts(a, x) +fmt.Printf("%d not found, can be inserted at index %d in %v\n", x, i, a) +</pre> <p>Output:</p> <pre class="output" data-language="go">found 2 at index 1 in [1 2 3 4 6 7 8] +5 not found, can be inserted at index 4 in [1 2 3 4 6 7 8] +</pre> <h2 id="SearchStrings">func <span>SearchStrings</span> </h2> <pre data-language="go">func SearchStrings(a []string, x string) int</pre> <p>SearchStrings searches for x in a sorted slice of strings and returns the index as specified by Search. The return value is the index to insert x if x is not present (it could be len(a)). The slice must be sorted in ascending order. </p> +<h2 id="Slice">func <span>Slice</span> <span title="Added in Go 1.8">1.8</span> </h2> <pre data-language="go">func Slice(x any, less func(i, j int) bool)</pre> <p>Slice sorts the slice x given the provided less function. It panics if x is not a slice. </p> +<p>The sort is not guaranteed to be stable: equal elements may be reversed from their original order. For a stable sort, use <a href="#SliceStable">SliceStable</a>. </p> +<p>The less function must satisfy the same requirements as the Interface type's Less method. </p> +<p>Note: in many situations, the newer <span>slices.SortFunc</span> function is more ergonomic and runs faster. </p> <h4 id="example_Slice"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">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) +</pre> <p>Output:</p> <pre class="output" data-language="go">By name: [{Alice 55} {Bob 75} {Gopher 7} {Vera 24}] +By age: [{Gopher 7} {Vera 24} {Alice 55} {Bob 75}] +</pre> <h2 id="SliceIsSorted">func <span>SliceIsSorted</span> <span title="Added in Go 1.8">1.8</span> </h2> <pre data-language="go">func SliceIsSorted(x any, less func(i, j int) bool) bool</pre> <p>SliceIsSorted reports whether the slice x is sorted according to the provided less function. It panics if x is not a slice. </p> +<p>Note: in many situations, the newer <span>slices.IsSortedFunc</span> function is more ergonomic and runs faster. </p> +<h2 id="SliceStable">func <span>SliceStable</span> <span title="Added in Go 1.8">1.8</span> </h2> <pre data-language="go">func SliceStable(x any, less func(i, j int) bool)</pre> <p>SliceStable sorts the slice x using the provided less function, keeping equal elements in their original order. It panics if x is not a slice. </p> +<p>The less function must satisfy the same requirements as the Interface type's Less method. </p> +<p>Note: in many situations, the newer <span>slices.SortStableFunc</span> function is more ergonomic and runs faster. </p> <h4 id="example_SliceStable"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">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) + +</pre> <p>Output:</p> <pre class="output" data-language="go">By name: [{Alice 25} {Alice 75} {Alice 75} {Bob 75} {Bob 25} {Colin 25} {Elizabeth 75} {Elizabeth 25}] +By age,name: [{Alice 25} {Bob 25} {Colin 25} {Elizabeth 25} {Alice 75} {Alice 75} {Bob 75} {Elizabeth 75}] +</pre> <h2 id="Sort">func <span>Sort</span> </h2> <pre data-language="go">func Sort(data Interface)</pre> <p>Sort sorts data in ascending order as determined by the Less method. It makes one call to data.Len to determine n and O(n*log(n)) calls to data.Less and data.Swap. The sort is not guaranteed to be stable. </p> +<p>Note: in many situations, the newer <span>slices.SortFunc</span> function is more ergonomic and runs faster. </p> +<h2 id="Stable">func <span>Stable</span> <span title="Added in Go 1.2">1.2</span> </h2> <pre data-language="go">func Stable(data Interface)</pre> <p>Stable sorts data in ascending order as determined by the Less method, while keeping the original order of equal elements. </p> +<p>It makes one call to data.Len to determine n, O(n*log(n)) calls to data.Less and O(n*log(n)*log(n)) calls to data.Swap. </p> +<p>Note: in many situations, the newer slices.SortStableFunc function is more ergonomic and runs faster. </p> +<h2 id="Strings">func <span>Strings</span> </h2> <pre data-language="go">func Strings(x []string)</pre> <p>Strings sorts a slice of strings in increasing order. </p> +<p>Note: as of Go 1.22, this function simply calls <span>slices.Sort</span>. </p> <h4 id="example_Strings"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">s := []string{"Go", "Bravo", "Gopher", "Alpha", "Grin", "Delta"} +sort.Strings(s) +fmt.Println(s) +</pre> <p>Output:</p> <pre class="output" data-language="go">[Alpha Bravo Delta Go Gopher Grin] +</pre> <h2 id="StringsAreSorted">func <span>StringsAreSorted</span> </h2> <pre data-language="go">func StringsAreSorted(x []string) bool</pre> <p>StringsAreSorted reports whether the slice x is sorted in increasing order. </p> +<p>Note: as of Go 1.22, this function simply calls <span>slices.IsSorted</span>. </p> +<h2 id="Float64Slice">type <span>Float64Slice</span> </h2> <p>Float64Slice implements Interface for a []float64, sorting in increasing order, with not-a-number (NaN) values ordered before other values. </p> +<pre data-language="go">type Float64Slice []float64</pre> <h3 id="Float64Slice.Len">func (Float64Slice) <span>Len</span> </h3> <pre data-language="go">func (x Float64Slice) Len() int</pre> <h3 id="Float64Slice.Less">func (Float64Slice) <span>Less</span> </h3> <pre data-language="go">func (x Float64Slice) Less(i, j int) bool</pre> <p>Less reports whether x[i] should be ordered before x[j], as required by the sort Interface. Note that floating-point comparison by itself is not a transitive relation: it does not report a consistent ordering for not-a-number (NaN) values. This implementation of Less places NaN values before any others, by using: </p> +<pre data-language="go">x[i] < x[j] || (math.IsNaN(x[i]) && !math.IsNaN(x[j])) +</pre> <h3 id="Float64Slice.Search">func (Float64Slice) <span>Search</span> </h3> <pre data-language="go">func (p Float64Slice) Search(x float64) int</pre> <p>Search returns the result of applying <a href="#SearchFloat64s">SearchFloat64s</a> to the receiver and x. </p> +<h3 id="Float64Slice.Sort">func (Float64Slice) <span>Sort</span> </h3> <pre data-language="go">func (x Float64Slice) Sort()</pre> <p>Sort is a convenience method: x.Sort() calls Sort(x). </p> +<h3 id="Float64Slice.Swap">func (Float64Slice) <span>Swap</span> </h3> <pre data-language="go">func (x Float64Slice) Swap(i, j int)</pre> <h2 id="IntSlice">type <span>IntSlice</span> </h2> <p>IntSlice attaches the methods of Interface to []int, sorting in increasing order. </p> +<pre data-language="go">type IntSlice []int</pre> <h3 id="IntSlice.Len">func (IntSlice) <span>Len</span> </h3> <pre data-language="go">func (x IntSlice) Len() int</pre> <h3 id="IntSlice.Less">func (IntSlice) <span>Less</span> </h3> <pre data-language="go">func (x IntSlice) Less(i, j int) bool</pre> <h3 id="IntSlice.Search">func (IntSlice) <span>Search</span> </h3> <pre data-language="go">func (p IntSlice) Search(x int) int</pre> <p>Search returns the result of applying <a href="#SearchInts">SearchInts</a> to the receiver and x. </p> +<h3 id="IntSlice.Sort">func (IntSlice) <span>Sort</span> </h3> <pre data-language="go">func (x IntSlice) Sort()</pre> <p>Sort is a convenience method: x.Sort() calls Sort(x). </p> +<h3 id="IntSlice.Swap">func (IntSlice) <span>Swap</span> </h3> <pre data-language="go">func (x IntSlice) Swap(i, j int)</pre> <h2 id="Interface">type <span>Interface</span> </h2> <p>An implementation of Interface can be sorted by the routines in this package. The methods refer to elements of the underlying collection by integer index. </p> +<pre data-language="go">type Interface interface { + // Len is the number of elements in the collection. + Len() int + + // Less reports whether the element with index i + // must sort before the element with index j. + // + // If both Less(i, j) and Less(j, i) are false, + // then the elements at index i and j are considered equal. + // Sort may place equal elements in any order in the final result, + // while Stable preserves the original input order of equal elements. + // + // Less must describe a transitive ordering: + // - if both Less(i, j) and Less(j, k) are true, then Less(i, k) must be true as well. + // - if both Less(i, j) and Less(j, k) are false, then Less(i, k) must be false as well. + // + // Note that floating-point comparison (the < operator on float32 or float64 values) + // is not a transitive ordering when not-a-number (NaN) values are involved. + // See Float64Slice.Less for a correct implementation for floating-point values. + Less(i, j int) bool + + // Swap swaps the elements with indexes i and j. + Swap(i, j int) +}</pre> <h3 id="Reverse">func <span>Reverse</span> <span title="Added in Go 1.1">1.1</span> </h3> <pre data-language="go">func Reverse(data Interface) Interface</pre> <p>Reverse returns the reverse order for data. </p> <h4 id="example_Reverse"> <span class="text">Example</span> +</h4> <p>Code:</p> <pre class="code" data-language="go">s := []int{5, 2, 6, 3, 1, 4} // unsorted +sort.Sort(sort.Reverse(sort.IntSlice(s))) +fmt.Println(s) +</pre> <p>Output:</p> <pre class="output" data-language="go">[6 5 4 3 2 1] +</pre> <h2 id="StringSlice">type <span>StringSlice</span> </h2> <p>StringSlice attaches the methods of Interface to []string, sorting in increasing order. </p> +<pre data-language="go">type StringSlice []string</pre> <h3 id="StringSlice.Len">func (StringSlice) <span>Len</span> </h3> <pre data-language="go">func (x StringSlice) Len() int</pre> <h3 id="StringSlice.Less">func (StringSlice) <span>Less</span> </h3> <pre data-language="go">func (x StringSlice) Less(i, j int) bool</pre> <h3 id="StringSlice.Search">func (StringSlice) <span>Search</span> </h3> <pre data-language="go">func (p StringSlice) Search(x string) int</pre> <p>Search returns the result of applying <a href="#SearchStrings">SearchStrings</a> to the receiver and x. </p> +<h3 id="StringSlice.Sort">func (StringSlice) <span>Sort</span> </h3> <pre data-language="go">func (x StringSlice) Sort()</pre> <p>Sort is a convenience method: x.Sort() calls Sort(x). </p> +<h3 id="StringSlice.Swap">func (StringSlice) <span>Swap</span> </h3> <pre data-language="go">func (x StringSlice) Swap(i, j int)</pre><div class="_attribution"> + <p class="_attribution-p"> + © Google, Inc.<br>Licensed under the Creative Commons Attribution License 3.0.<br> + <a href="http://golang.org/pkg/sort/" class="_attribution-link">http://golang.org/pkg/sort/</a> + </p> +</div> |