slices

package standard library
go1.23.3 Latest Latest
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 Go to latest Published: Nov 6, 2024 License: BSD-3-Clause Imports: 4 Imported by: 25,282

Documentation

Overview

Package slices defines various functions useful with slices of any type.

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func All added in go1.23.0 

func All[Slice ~[]E, E any](s Slice) iter.Seq2[int, E]

All returns an iterator over index-value pairs in the slice in the usual order.

func AppendSeq added in go1.23.0 

func AppendSeq[Slice ~[]E, E any](s Slice, seq iter.Seq[E]) Slice

AppendSeq appends the values from seq to the slice and returns the extended slice.

func Backward added in go1.23.0 

func Backward[Slice ~[]E, E any](s Slice) iter.Seq2[int, E]

Backward returns an iterator over index-value pairs in the slice, traversing it backward with descending indices.

func BinarySearch 

func BinarySearch[S ~[]E, E cmp.Ordered](x S, target E) (int, bool)

BinarySearch searches for target in a sorted slice and returns the earliest position where target is found, or the position where target would appear in the sort order; it also returns a bool saying whether the target is really found in the slice. The slice must be sorted in increasing order.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	names := []string{"Alice", "Bob", "Vera"}
	n, found := slices.BinarySearch(names, "Vera")
	fmt.Println("Vera:", n, found)
	n, found = slices.BinarySearch(names, "Bill")
	fmt.Println("Bill:", n, found)
}

Output:

Vera: 2 true
Bill: 1 false

func BinarySearchFunc 

func BinarySearchFunc[S ~[]E, E, T any](x S, target T, cmp func(E, T) int) (int, bool)

BinarySearchFunc works like BinarySearch, but uses a custom comparison function. The slice must be sorted in increasing order, where "increasing" is defined by cmp. cmp should return 0 if the slice element matches the target, a negative number if the slice element precedes the target, or a positive number if the slice element follows the target. cmp must implement the same ordering as the slice, such that if cmp(a, t) < 0 and cmp(b, t) >= 0, then a must precede b in the slice.

Example 
package main

import (
	"fmt"
	"slices"
	"strings"
)

func main() {
	type Person struct {
		Name string
		Age  int
	}
	people := []Person{
		{"Alice", 55},
		{"Bob", 24},
		{"Gopher", 13},
	}
	n, found := slices.BinarySearchFunc(people, Person{"Bob", 0}, func(a, b Person) int {
		return strings.Compare(a.Name, b.Name)
	})
	fmt.Println("Bob:", n, found)
}

Output:

Bob: 1 true

func Chunk added in go1.23.0 

func Chunk[Slice ~[]E, E any](s Slice, n int) iter.Seq[Slice]

Chunk returns an iterator over consecutive sub-slices of up to n elements of s. All but the last sub-slice will have size n. All sub-slices are clipped to have no capacity beyond the length. If s is empty, the sequence is empty: there is no empty slice in the sequence. Chunk panics if n is less than 1.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	type Person struct {
		Name string
		Age  int
	}

	type People []Person

	people := People{
		{"Gopher", 13},
		{"Alice", 20},
		{"Bob", 5},
		{"Vera", 24},
		{"Zac", 15},
	}

	// Chunk people into []Person 2 elements at a time.
	for c := range slices.Chunk(people, 2) {
		fmt.Println(c)
	}

}

Output:

[{Gopher 13} {Alice 20}]
[{Bob 5} {Vera 24}]
[{Zac 15}]

func Clip 

func Clip[S ~[]E, E any](s S) S

Clip removes unused capacity from the slice, returning s[:len(s):len(s)].

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	a := [...]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
	s := a[:4:10]
	clip := slices.Clip(s)
	fmt.Println(cap(s))
	fmt.Println(clip)
	fmt.Println(len(clip))
	fmt.Println(cap(clip))
}

Output:

10
[0 1 2 3]
4
4

func Clone 

func Clone[S ~[]E, E any](s S) S

Clone returns a copy of the slice. The elements are copied using assignment, so this is a shallow clone. The result may have additional unused capacity.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, -10, 8}
	clone := slices.Clone(numbers)
	fmt.Println(clone)
	clone[2] = 10
	fmt.Println(numbers)
}

Output:

[0 42 -10 8]
[0 42 -10 8]

func Collect added in go1.23.0 

func Collect[E any](seq iter.Seq[E]) []E

Collect collects values from seq into a new slice and returns it.

func Compact 

func Compact[S ~[]E, E comparable](s S) S

Compact replaces consecutive runs of equal elements with a single copy. This is like the uniq command found on Unix. Compact modifies the contents of the slice s and returns the modified slice, which may have a smaller length. Compact zeroes the elements between the new length and the original length.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	seq := []int{0, 1, 1, 2, 3, 5, 8}
	seq = slices.Compact(seq)
	fmt.Println(seq)
}

Output:

[0 1 2 3 5 8]

func CompactFunc 

func CompactFunc[S ~[]E, E any](s S, eq func(E, E) bool) S

CompactFunc is like Compact but uses an equality function to compare elements. For runs of elements that compare equal, CompactFunc keeps the first one. CompactFunc zeroes the elements between the new length and the original length.

Example 
package main

import (
	"fmt"
	"slices"
	"strings"
)

func main() {
	names := []string{"bob", "Bob", "alice", "Vera", "VERA"}
	names = slices.CompactFunc(names, strings.EqualFold)
	fmt.Println(names)
}

Output:

[bob alice Vera]

func Compare 

func Compare[S ~[]E, E cmp.Ordered](s1, s2 S) int

Compare compares the elements of s1 and s2, using cmp.Compare on each pair of elements. The elements are compared sequentially, starting at index 0, until one element is not equal to the other. The result of comparing the first non-matching elements is returned. If both slices are equal until one of them ends, the shorter slice is considered less than the longer one. The result is 0 if s1 == s2, -1 if s1 < s2, and +1 if s1 > s2.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	names := []string{"Alice", "Bob", "Vera"}
	fmt.Println("Equal:", slices.Compare(names, []string{"Alice", "Bob", "Vera"}))
	fmt.Println("V < X:", slices.Compare(names, []string{"Alice", "Bob", "Xena"}))
	fmt.Println("V > C:", slices.Compare(names, []string{"Alice", "Bob", "Cat"}))
	fmt.Println("3 > 2:", slices.Compare(names, []string{"Alice", "Bob"}))
}

Output:

Equal: 0
V < X: -1
V > C: 1
3 > 2: 1

func CompareFunc 

func CompareFunc[S1 ~[]E1, S2 ~[]E2, E1, E2 any](s1 S1, s2 S2, cmp func(E1, E2) int) int

CompareFunc is like Compare but uses a custom comparison function on each pair of elements. The result is the first non-zero result of cmp; if cmp always returns 0 the result is 0 if len(s1) == len(s2), -1 if len(s1) < len(s2), and +1 if len(s1) > len(s2).

Example 
package main

import (
	"cmp"
	"fmt"
	"slices"
	"strconv"
)

func main() {
	numbers := []int{0, 43, 8}
	strings := []string{"0", "0", "8"}
	result := slices.CompareFunc(numbers, strings, func(n int, s string) int {
		sn, err := strconv.Atoi(s)
		if err != nil {
			return 1
		}
		return cmp.Compare(n, sn)
	})
	fmt.Println(result)
}

Output:

1

func Concat added in go1.22.0 

func Concat[S ~[]E, E any](slices ...S) S

Concat returns a new slice concatenating the passed in slices.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	s1 := []int{0, 1, 2, 3}
	s2 := []int{4, 5, 6}
	concat := slices.Concat(s1, s2)
	fmt.Println(concat)
}

Output:

[0 1 2 3 4 5 6]

func Contains 

func Contains[S ~[]E, E comparable](s S, v E) bool

Contains reports whether v is present in s.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 1, 2, 3}
	fmt.Println(slices.Contains(numbers, 2))
	fmt.Println(slices.Contains(numbers, 4))
}

Output:

true
false

func ContainsFunc 

func ContainsFunc[S ~[]E, E any](s S, f func(E) bool) bool

ContainsFunc reports whether at least one element e of s satisfies f(e).

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, -10, 8}
	hasNegative := slices.ContainsFunc(numbers, func(n int) bool {
		return n < 0
	})
	fmt.Println("Has a negative:", hasNegative)
	hasOdd := slices.ContainsFunc(numbers, func(n int) bool {
		return n%2 != 0
	})
	fmt.Println("Has an odd number:", hasOdd)
}

Output:

Has a negative: true
Has an odd number: false

func Delete 

func Delete[S ~[]E, E any](s S, i, j int) S

Delete removes the elements s[i:j] from s, returning the modified slice. Delete panics if j > len(s) or s[i:j] is not a valid slice of s. Delete is O(len(s)-i), so if many items must be deleted, it is better to make a single call deleting them all together than to delete one at a time. Delete zeroes the elements s[len(s)-(j-i):len(s)].

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	letters := []string{"a", "b", "c", "d", "e"}
	letters = slices.Delete(letters, 1, 4)
	fmt.Println(letters)
}

Output:

[a e]

func DeleteFunc 

func DeleteFunc[S ~[]E, E any](s S, del func(E) bool) S

DeleteFunc removes any elements from s for which del returns true, returning the modified slice. DeleteFunc zeroes the elements between the new length and the original length.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	seq := []int{0, 1, 1, 2, 3, 5, 8}
	seq = slices.DeleteFunc(seq, func(n int) bool {
		return n%2 != 0 // delete the odd numbers
	})
	fmt.Println(seq)
}

Output:

[0 2 8]

func Equal 

func Equal[S ~[]E, E comparable](s1, s2 S) bool

Equal reports whether two slices are equal: the same length and all elements equal. If the lengths are different, Equal returns false. Otherwise, the elements are compared in increasing index order, and the comparison stops at the first unequal pair. Empty and nil slices are considered equal. Floating point NaNs are not considered equal.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, 8}
	fmt.Println(slices.Equal(numbers, []int{0, 42, 8}))
	fmt.Println(slices.Equal(numbers, []int{10}))
}

Output:

true
false

func EqualFunc 

func EqualFunc[S1 ~[]E1, S2 ~[]E2, E1, E2 any](s1 S1, s2 S2, eq func(E1, E2) bool) bool

EqualFunc reports whether two slices are equal using an equality function on each pair of elements. If the lengths are different, EqualFunc returns false. Otherwise, the elements are compared in increasing index order, and the comparison stops at the first index for which eq returns false.

Example 
package main

import (
	"fmt"
	"slices"
	"strconv"
)

func main() {
	numbers := []int{0, 42, 8}
	strings := []string{"000", "42", "0o10"}
	equal := slices.EqualFunc(numbers, strings, func(n int, s string) bool {
		sn, err := strconv.ParseInt(s, 0, 64)
		if err != nil {
			return false
		}
		return n == int(sn)
	})
	fmt.Println(equal)
}

Output:

true

func Grow 

func Grow[S ~[]E, E any](s S, n int) S

Grow increases the slice's capacity, if necessary, to guarantee space for another n elements. After Grow(n), at least n elements can be appended to the slice without another allocation. If n is negative or too large to allocate the memory, Grow panics.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, -10, 8}
	grow := slices.Grow(numbers, 2)
	fmt.Println(cap(numbers))
	fmt.Println(grow)
	fmt.Println(len(grow))
	fmt.Println(cap(grow))
}

Output:

4
[0 42 -10 8]
4
8

func Index 

func Index[S ~[]E, E comparable](s S, v E) int

Index returns the index of the first occurrence of v in s, or -1 if not present.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, 8}
	fmt.Println(slices.Index(numbers, 8))
	fmt.Println(slices.Index(numbers, 7))
}

Output:

2
-1

func IndexFunc 

func IndexFunc[S ~[]E, E any](s S, f func(E) bool) int

IndexFunc returns the first index i satisfying f(s[i]), or -1 if none do.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, -10, 8}
	i := slices.IndexFunc(numbers, func(n int) bool {
		return n < 0
	})
	fmt.Println("First negative at index", i)
}

Output:

First negative at index 2

func Insert 

func Insert[S ~[]E, E any](s S, i int, v ...E) S

Insert inserts the values v... into s at index i, returning the modified slice. The elements at s[i:] are shifted up to make room. In the returned slice r, r[i] == v[0], and r[i+len(v)] == value originally at r[i]. Insert panics if i is out of range. This function is O(len(s) + len(v)).

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	names := []string{"Alice", "Bob", "Vera"}
	names = slices.Insert(names, 1, "Bill", "Billie")
	names = slices.Insert(names, len(names), "Zac")
	fmt.Println(names)
}

Output:

[Alice Bill Billie Bob Vera Zac]

func IsSorted 

func IsSorted[S ~[]E, E cmp.Ordered](x S) bool

IsSorted reports whether x is sorted in ascending order.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	fmt.Println(slices.IsSorted([]string{"Alice", "Bob", "Vera"}))
	fmt.Println(slices.IsSorted([]int{0, 2, 1}))
}

Output:

true
false

func IsSortedFunc 

func IsSortedFunc[S ~[]E, E any](x S, cmp func(a, b E) int) bool

IsSortedFunc reports whether x is sorted in ascending order, with cmp as the comparison function as defined by SortFunc.

Example 
package main

import (
	"fmt"
	"slices"
	"strings"
)

func main() {
	names := []string{"alice", "Bob", "VERA"}
	isSortedInsensitive := slices.IsSortedFunc(names, func(a, b string) int {
		return strings.Compare(strings.ToLower(a), strings.ToLower(b))
	})
	fmt.Println(isSortedInsensitive)
	fmt.Println(slices.IsSorted(names))
}

Output:

true
false

func Max 

func Max[S ~[]E, E cmp.Ordered](x S) E

Max returns the maximal value in x. It panics if x is empty. For floating-point E, Max propagates NaNs (any NaN value in x forces the output to be NaN).

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, -10, 8}
	fmt.Println(slices.Max(numbers))
}

Output:

42

func MaxFunc 

func MaxFunc[S ~[]E, E any](x S, cmp func(a, b E) int) E

MaxFunc returns the maximal value in x, using cmp to compare elements. It panics if x is empty. If there is more than one maximal element according to the cmp function, MaxFunc returns the first one.

Example 
package main

import (
	"cmp"
	"fmt"
	"slices"
)

func main() {
	type Person struct {
		Name string
		Age  int
	}
	people := []Person{
		{"Gopher", 13},
		{"Alice", 55},
		{"Vera", 24},
		{"Bob", 55},
	}
	firstOldest := slices.MaxFunc(people, func(a, b Person) int {
		return cmp.Compare(a.Age, b.Age)
	})
	fmt.Println(firstOldest.Name)
}

Output:

Alice

func Min 

func Min[S ~[]E, E cmp.Ordered](x S) E

Min returns the minimal value in x. It panics if x is empty. For floating-point numbers, Min propagates NaNs (any NaN value in x forces the output to be NaN).

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 42, -10, 8}
	fmt.Println(slices.Min(numbers))
}

Output:

-10

func MinFunc 

func MinFunc[S ~[]E, E any](x S, cmp func(a, b E) int) E

MinFunc returns the minimal value in x, using cmp to compare elements. It panics if x is empty. If there is more than one minimal element according to the cmp function, MinFunc returns the first one.

Example 
package main

import (
	"cmp"
	"fmt"
	"slices"
)

func main() {
	type Person struct {
		Name string
		Age  int
	}
	people := []Person{
		{"Gopher", 13},
		{"Bob", 5},
		{"Vera", 24},
		{"Bill", 5},
	}
	firstYoungest := slices.MinFunc(people, func(a, b Person) int {
		return cmp.Compare(a.Age, b.Age)
	})
	fmt.Println(firstYoungest.Name)
}

Output:

Bob

func Repeat added in go1.23.0 

func Repeat[S ~[]E, E any](x S, count int) S

Repeat returns a new slice that repeats the provided slice the given number of times. The result has length and capacity (len(x) * count). The result is never nil. Repeat panics if count is negative or if the result of (len(x) * count) overflows.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	numbers := []int{0, 1, 2, 3}
	repeat := slices.Repeat(numbers, 2)
	fmt.Println(repeat)
}

Output:

[0 1 2 3 0 1 2 3]

func Replace 

func Replace[S ~[]E, E any](s S, i, j int, v ...E) S

Replace replaces the elements s[i:j] by the given v, and returns the modified slice. Replace panics if j > len(s) or s[i:j] is not a valid slice of s. When len(v) < (j-i), Replace zeroes the elements between the new length and the original length.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	names := []string{"Alice", "Bob", "Vera", "Zac"}
	names = slices.Replace(names, 1, 3, "Bill", "Billie", "Cat")
	fmt.Println(names)
}

Output:

[Alice Bill Billie Cat Zac]

func Reverse 

func Reverse[S ~[]E, E any](s S)

Reverse reverses the elements of the slice in place.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	names := []string{"alice", "Bob", "VERA"}
	slices.Reverse(names)
	fmt.Println(names)
}

Output:

[VERA Bob alice]

func Sort 

func Sort[S ~[]E, E cmp.Ordered](x S)

Sort sorts a slice of any ordered type in ascending order. When sorting floating-point numbers, NaNs are ordered before other values.

Example 
package main

import (
	"fmt"
	"slices"
)

func main() {
	smallInts := []int8{0, 42, -10, 8}
	slices.Sort(smallInts)
	fmt.Println(smallInts)
}

Output:

[-10 0 8 42]

func SortFunc 

func SortFunc[S ~[]E, E any](x S, cmp func(a, b E) int)

SortFunc sorts the slice x in ascending order as determined by the cmp function. This sort is not guaranteed to be stable. cmp(a, b) should return a negative number when a < b, a positive number when a > b and zero when a == b or a and b are incomparable in the sense of a strict weak ordering.

SortFunc requires that cmp is a strict weak ordering. See https://en.wikipedia.org/wiki/Weak_ordering#Strict_weak_orderings. The function should return 0 for incomparable items.

Example (CaseInsensitive) 
package main

import (
	"fmt"
	"slices"
	"strings"
)

func main() {
	names := []string{"Bob", "alice", "VERA"}
	slices.SortFunc(names, func(a, b string) int {
		return strings.Compare(strings.ToLower(a), strings.ToLower(b))
	})
	fmt.Println(names)
}

Output:

[alice Bob VERA]
Example (MultiField) 
package main

import (
	"cmp"
	"fmt"
	"slices"
	"strings"
)

func main() {
	type Person struct {
		Name string
		Age  int
	}
	people := []Person{
		{"Gopher", 13},
		{"Alice", 55},
		{"Bob", 24},
		{"Alice", 20},
	}
	slices.SortFunc(people, func(a, b Person) int {
		if n := strings.Compare(a.Name, b.Name); n != 0 {
			return n
		}
		// If names are equal, order by age
		return cmp.Compare(a.Age, b.Age)
	})
	fmt.Println(people)
}

Output:

[{Alice 20} {Alice 55} {Bob 24} {Gopher 13}]

func SortStableFunc 

func SortStableFunc[S ~[]E, E any](x S, cmp func(a, b E) int)

SortStableFunc sorts the slice x while keeping the original order of equal elements, using cmp to compare elements in the same way as SortFunc.

Example 
package main

import (
	"fmt"
	"slices"
	"strings"
)

func main() {
	type Person struct {
		Name string
		Age  int
	}
	people := []Person{
		{"Gopher", 13},
		{"Alice", 20},
		{"Bob", 24},
		{"Alice", 55},
	}
	// Stable sort by name, keeping age ordering of Alices intact
	slices.SortStableFunc(people, func(a, b Person) int {
		return strings.Compare(a.Name, b.Name)
	})
	fmt.Println(people)
}

Output:

[{Alice 20} {Alice 55} {Bob 24} {Gopher 13}]

func Sorted added in go1.23.0 

func Sorted[E cmp.Ordered](seq iter.Seq[E]) []E

Sorted collects values from seq into a new slice, sorts the slice, and returns it.

func SortedFunc added in go1.23.0 

func SortedFunc[E any](seq iter.Seq[E], cmp func(E, E) int) []E

SortedFunc collects values from seq into a new slice, sorts the slice using the comparison function, and returns it.

func SortedStableFunc added in go1.23.0 

func SortedStableFunc[E any](seq iter.Seq[E], cmp func(E, E) int) []E

SortedStableFunc collects values from seq into a new slice. It then sorts the slice while keeping the original order of equal elements, using the comparison function to compare elements. It returns the new slice.

func Values added in go1.23.0 

func Values[Slice ~[]E, E any](s Slice) iter.Seq[E]

Values returns an iterator that yields the slice elements in order.

Types

This section is empty.

Source Files

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