fmt.Println("Enter position to delete::")
fmt.Scanln(&pos)
new_arr := make([]int, (len(arr) - 1))
k := 0
for i := 0; i < (len(arr) - 1); {
if i != pos {
new_arr[i] = arr[k]
k++
i++
} else {
k++
}
}
for i := 0; i < (len(arr) - 1); i++ {
fmt.Println(new_arr[i])
}
I am using this command to delete an element from a Slice but it is not working, please suggest.
Order matters
If you want to keep your array ordered, you have to shift all of the elements at the right of the deleting index by one to the left. Hopefully, this can be done easily in Golang:
func remove(slice []int, s int) []int {
return append(slice[:s], slice[s+1:]...)
}
However, this is inefficient because you may end up with moving all of the elements, which is costly.
Order is not important
If you do not care about ordering, you have the much faster possibility to replace the element to delete with the one at the end of the slice and then return the n-1 first elements:
func remove(s []int, i int) []int {
s[i] = s[len(s)-1]
return s[:len(s)-1]
}
With the reslicing method, emptying an array of 1 000 000 elements take 224s, with this one it takes only 0.06ns.
This answer does not perform bounds-checking. It expects a valid index as input. This means that negative values or indices that are greater or equal to the initial len(s) will cause Go to panic.
Slices and arrays being 0-indexed, removing the n-th element of an array implies to provide input n-1. To remove the first element, call remove(s, 0), to remove the second, call remove(s, 1), and so on and so forth.
return s[1:] which also does not answer the original question. –
Lyso s[i] = s[len(s)-1] definitely copies the last element to the element at index i. Then, return s[:len(s)-1] returns the slice without the last element. Two statements there. –
Canonicity s[len(s)-1], s[i] = 0, s[len(s)-1]. Especially so if you're working with non-primitive arrays. If you had pointers to something it's better to make the element you want to remove nil before slicing so you don't have pointers in the underlying array. This answer explains why very well. In short: after moving the last element at the deleted element's location, zero the last element before slicing. –
Reproachless a := [5]int{1, 2, 3, 4}; b := a[:]; b = remove(b, 2) I was expecting to result in [1, 2, 4] in my slice but got [1,2,0,4] instead: go.dev/play/p/SZGjzbxYbqR –
Brauer This is a little strange to see but most answers here are dangerous and gloss over what they are actually doing. Looking at the original question that was asked about removing an item from the slice a copy of the slice is being made and then it's being filled. This ensures that as the slices are passed around your program you don't introduce subtle bugs.
Here is some code comparing users answers in this thread and the original post. Here is a go playground to mess around with this code in.
package main
import (
"fmt"
)
func RemoveIndex(s []int, index int) []int {
return append(s[:index], s[index+1:]...)
}
func main() {
all := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
removeIndex := RemoveIndex(all, 5)
fmt.Println("all: ", all) //[0 1 2 3 4 6 7 8 9 9]
fmt.Println("removeIndex: ", removeIndex) //[0 1 2 3 4 6 7 8 9]
removeIndex[0] = 999
fmt.Println("all: ", all) //[999 1 2 3 4 6 7 9 9]
fmt.Println("removeIndex: ", removeIndex) //[999 1 2 3 4 6 7 8 9]
}
In the above example you can see me create a slice and fill it manually with numbers 0 to 9. We then remove index 5 from all and assign it to remove index. However when we go to print out all now we see that it has been modified as well. This is because slices are pointers to an underlying array. Writing it out to removeIndex causes all to be modified as well with the difference being all is longer by one element that is no longer reachable from removeIndex. Next we change a value in removeIndex and we can see all gets modified as well. Effective go goes into some more detail on this.
The following example I won't go into but it does the same thing for our purposes. And just illustrates that using copy is no different.
package main
import (
"fmt"
)
func RemoveCopy(slice []int, i int) []int {
copy(slice[i:], slice[i+1:])
return slice[:len(slice)-1]
}
func main() {
all := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
removeCopy := RemoveCopy(all, 5)
fmt.Println("all: ", all) //[0 1 2 3 4 6 7 8 9 9]
fmt.Println("removeCopy: ", removeCopy) //[0 1 2 3 4 6 7 8 9]
removeCopy[0] = 999
fmt.Println("all: ", all) //[99 1 2 3 4 6 7 9 9]
fmt.Println("removeCopy: ", removeCopy) //[999 1 2 3 4 6 7 8 9]
}
Looking at the original question it does not modify the slice that it's removing an item from. Making the original answer in this thread the best so far for most people coming to this page.
package main
import (
"fmt"
)
func OriginalRemoveIndex(arr []int, pos int) []int {
new_arr := make([]int, (len(arr) - 1))
k := 0
for i := 0; i < (len(arr) - 1); {
if i != pos {
new_arr[i] = arr[k]
k++
} else {
k++
}
i++
}
return new_arr
}
func main() {
all := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
originalRemove := OriginalRemoveIndex(all, 5)
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
fmt.Println("originalRemove: ", originalRemove) //[0 1 2 3 4 6 7 8 9]
originalRemove[0] = 999
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
fmt.Println("originalRemove: ", originalRemove) //[999 1 2 3 4 6 7 8 9]
}
As you can see this output acts as most people would expect and likely what most people want. Modification of originalRemove doesn't cause changes in all and the operation of removing the index and assigning it doesn't cause changes as well! Fantastic!
This code is a little lengthy though so the above can be changed to this.
package main
import (
"fmt"
)
func RemoveIndex(s []int, index int) []int {
ret := make([]int, 0)
ret = append(ret, s[:index]...)
return append(ret, s[index+1:]...)
}
func main() {
all := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
removeIndex := RemoveIndex(all, 5)
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
fmt.Println("removeIndex: ", removeIndex) //[0 1 2 3 4 6 7 8 9]
removeIndex[0] = 999
fmt.Println("all: ", all) //[0 1 2 3 4 5 6 7 8 9]
fmt.Println("removeIndex: ", removeIndex) //[999 1 2 3 4 6 7 8 9]
}
Almost identical to the original remove index solution however we make a new slice to append to before returning.
Remove one element from the Slice (this is called 're-slicing'):
package main
import (
"fmt"
)
func RemoveIndex(s []int, index int) []int {
return append(s[:index], s[index+1:]...)
}
func main() {
all := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
fmt.Println(all) //[0 1 2 3 4 5 6 7 8 9]
all = RemoveIndex(all, 5)
fmt.Println(all) //[0 1 2 3 4 6 7 8 9]
}
2019/09/28 19:46:25 http: panic serving 192.168.1.3:52817: runtime error: slice bounds out of range [7:5] goroutine 7 [running]: –
Solanum panic(). Please see Oleksandr's answer instead. –
Dolphin Using Delete from the slices package (stable since Go 1.21, on older Go versions you have to import golang.org/x/exp/slices):
slice := []int{1, 2, 3, 4}
slice = slices.Delete(slice, 1, 2)
fmt.Println(slice) // [1 3 4]
slices.Delete(s, i, j) removes the elements s[i:j] from s
Note two things:
Delete modifies the contents of the original sliceslice, otherwise it will have the wrong lengthappend(slice[:s], slice[s+1:]...). More info: cs.opensource.google/go/x/exp/+/0b5c67f0:slices/slices.go;l=156 –
Weinreb Delete function where it states : Delete might not modify the elements s[len(s)-(j-i):len(s)]. - just something to keep in mind when You need to resize (upwards) slice again eample –
Calipee append, now it includes zeroing the elements to allow GC: cs.opensource.google/go/x/exp/+/… –
Clodhopper Minor point (code golf), but in the case where order does not matter you don't need to swap the values. Just overwrite the array position being removed with a duplicate of the last position and then return a truncated array.
func remove(s []int, i int) []int {
s[i] = s[len(s)-1]
return s[:len(s)-1]
}
Same result.
s[i] = s[0], then return an array with only the last n-1 elements. return s[1:] –
Grummet s[1:] versus s[:len(s)-1] is that the later will perform much better if the slice later gets appended or deletes are intermingled with appends. The later keeps the slice capacity where-as the former doesn't. –
Reprimand This is how you Delete From a slice the idiomatic way. You don't need to build a function it is built into the append. Try it here https://play.golang.org/p/QMXn9-6gU5P
z := []int{9, 8, 7, 6, 5, 3, 2, 1, 0}
fmt.Println(z) //will print Answer [9 8 7 6 5 3 2 1 0]
z = append(z[:2], z[4:]...)
fmt.Println(z) //will print Answer [9 8 5 3 2 1 0]
From the book The Go Programming Language
To remove an element from the middle of a slice, preserving the order of the remaining elements, use copy to slide the higher-numbered elements down by one to fill the gap:
func remove(slice []int, i int) []int { copy(slice[i:], slice[i+1:]) return slice[:len(slice)-1] }
append can modify the backing array, so why can't remove? go.dev/play/p/9eQStgiqYYK –
Hunyadi s2 = append(s2, 2) and if you omit this step, the backing array s2 remains unchanged. Compare with go.dev/play/p/7EubNjwOFuD –
Almucantar :cap(s2) from the print statements in go.dev/play/p/v0JR88kuDyB, then it appears that s2 is not being updated. So is it safe to say that the backing array is updated, but the slice is not? –
Ingmar I take the below approach to remove the item in slice. This helps in readability for others. And also immutable.
func remove(items []string, item string) []string {
newitems := []string{}
for _, i := range items {
if i != item {
newitems = append(newitems, i)
}
}
return newitems
}
The best way to do it is to use the append function:
package main
import (
"fmt"
)
func main() {
x := []int{4, 5, 6, 7, 88}
fmt.Println(x)
x = append(x[:2], x[4:]...)//deletes 6 and 7
fmt.Println(x)
}
Using generics you can pass any type of slice.
// Removes slice element at index(s) and returns new slice
func remove[T any](slice []T, s int) []T {
return append(slice[:s], slice[s+1:]...)
}
Usage
slice := []int{1, 2, 3, 4}
result := remove(slice, 0)
fmt.Println(result)
// [2 3 4]
The currently most voted answer by T. Claverie is correct but I find the algorithm more clear if swap is performed only if needed, i.e. for all but the last element of the slice. This can be achieved by a simple if guard.
Order is not important/ no boundary checks perfomed
func remove(s []int, i int) []int {
// bring element to remove at the end if it's not there yet
if i != len(s)-1 {
s[i] = s[len(s)-1]
}
// drop the last element
return s[:len(s)-1]
}
Find a way here without relocating.
a := []string{"A", "B", "C", "D", "E"}
i := 2
// Remove the element at index i from a.
a[i] = a[len(a)-1] // Copy last element to index i.
a[len(a)-1] = "" // Erase last element (write zero value).
a = a[:len(a)-1] // Truncate slice.
fmt.Println(a) // [A B E D]
a := []string{"A", "B", "C", "D", "E"}
i := 2
// Remove the element at index i from a.
copy(a[i:], a[i+1:]) // Shift a[i+1:] left one index.
a[len(a)-1] = "" // Erase last element (write zero value).
a = a[:len(a)-1] // Truncate slice.
fmt.Println(a) // [A B D E]
Maybe you can try this method:
// DelEleInSlice delete an element from slice by index
// - arr: the reference of slice
// - index: the index of element will be deleted
func DelEleInSlice(arr interface{}, index int) {
vField := reflect.ValueOf(arr)
value := vField.Elem()
if value.Kind() == reflect.Slice || value.Kind() == reflect.Array {
result := reflect.AppendSlice(value.Slice(0, index), value.Slice(index+1, value.Len()))
value.Set(result)
}
}
Usage:
arrInt := []int{0, 1, 2, 3, 4, 5}
arrStr := []string{"0", "1", "2", "3", "4", "5"}
DelEleInSlice(&arrInt, 3)
DelEleInSlice(&arrStr, 4)
fmt.Println(arrInt)
fmt.Println(arrStr)
Result:
0, 1, 2, 4, 5
"0", "1", "2", "3", "5"
var value reflect.Value = reflect.ValueOf(array).Elem(); value.Set(reflect.AppendSlice(value.Slice(0, index), value.Slice(index+1, value.Len()))). –
Whimsicality for index, item := range movies{
if item.ID == "123"{
movies = append(movies[:index], movies[index+1:]...)
break
}
}
As of Go 1.22, you no longer have to do this yourself. The team have introduced the type agnostic Delete() function for slices. To delete an element or set of elements, pass in the slice to be modified along with a start an end index for items to be removed.
mySlice = slices.Delete(myslice, 1, 1)
Maybe this code will help.
It deletes item with a given index.
Takes the array, and the index to delete and returns a new array pretty much like append function.
func deleteItem(arr []int, index int) []int{
if index < 0 || index >= len(arr){
return []int{-1}
}
for i := index; i < len(arr) -1; i++{
arr[i] = arr[i + 1]
}
return arr[:len(arr)-1]
}
Here you can play with the code : https://play.golang.org/p/aX1Qj40uTVs
In the language tutorial we learn that:
Slices are like references to arrays. A slice does not store any data, it just describes a section of an underlying array. Changing the elements of a slice modifies the corresponding elements of its underlying array.
For this reason, working with the append function on slices without taking care of the origin and destination of the values we are dealing with is very dangerous as well as wrong for the Go philosophy.
The correct solution is therefore to work with a slice referenced to a new array and not the "main" one.
This is possible by creating a new slice through the make construct.
func removeAt(slice []int, index int) []int {
newSlice := make([]int, 0) //Create a new slice of type []int and length 0
newSlice = append(newSlice, slice[:index]...) //Copies the values contained in the old slice to the new slice up to the index (excluded)
if index != len(slice)-1 {
newSlice = append(newSlice, slice[index+1:]...) //If the index to be removed was different from the last one, then proceed to copy the following values of the index to the end of the old slice
}
return newSlice
}
In this way we are able to safely remove an element of a slice, regardless of the use we will make on the return of the function.
Since I used a function to answer the question, it would be a good idea to handle any errors as follows:
func removeAt(slice []int, index int) ([]int, error) {
if index < 0 {
return nil, fmt.Errorf("index (%d) cannot be a negative number", index)
}
if index >= len(slice) {
return nil, fmt.Errorf("index (%d) cannot be a number greater or equal than the length of slice (%d)", index, len(slice))
}
newSlice := make([]int, 0)
newSlice = append(newSlice, slice[:index]...)
if index != len(slice)-1 {
newSlice = append(newSlice, slice[index+1:]...)
}
return newSlice, nil
}
Or better yet, implement the function that can handle multiple types through interfaces. However, all this is a good practice since you build a function to do this, which does not concern the question posed.
However, an example of a test on the Go playground can be found here.
My two cents here, after the introduction of generics the lodash library has become way too powerful therefore:
mySlice = lo.Without[T](myslice, mySlice[indexOfTheElementToRemove])
where T the type of mySlice (if it is not a custom type I think it is automatically inferred so the T may not be needed).
No need to check every single element unless you care contents and you can utilize slice append. try it out
pos := 0
arr := []int{1, 2, 3, 4, 5, 6, 7, 9}
fmt.Println("input your position")
fmt.Scanln(&pos)
/* you need to check if negative input as well */
if (pos < len(arr)){
arr = append(arr[:pos], arr[pos+1:]...)
} else {
fmt.Println("position invalid")
}
You need to change your code a little bit,
new_arr := make([]int, (len(arr) - 1))
for i := 0; i < len(arr); i++ {
if i != pos {
new_arr = append(new_arr, arr[i])
}
}
For a more efficient loop you can use this
for i, item := range arr {
...
}
At last you can do it by using native slice functionality
new_arr = append(arr[:2], arr[3:])
The last solution remove element in the index 2 and put the new slice in new_arr.
This is the correct and best way to delete an element from the list.Because other ways can shift the elements while deleting. So try following method if Order matters.
func remove(s []int, index int) []int{{ return append(s[:index], s[index+1:]...) }
Basically you just assign to your slice the same slice but one item shorter:
data = data[:len(data)-1]
This is for remove items by value
(go 1.21)
func sliceRemove[T comparable](s *[]T, rmItems ...T) {
var end bool
for {
end = true
for i, elem := range *s {
for _, rmData := range rmItems {
if elem == rmData {
*s = slices.Delete(*s, i, i+1)
end = false
break
}
}
if !end {
break
}
}
if end {
break
}
}
}
func Example_sliceRemove() {
slice := []string{"Apple", "Bar", "Foo", "Foo", "Bar", "Banana"}
sliceRemove(&slice, "Bar", "Foo")
fmt.Println(slice)
// Output:
// [Apple Banana]
}
banchMark
func sliceRemove[T comparable](s *[]T, rmItems ...T) {
var end bool
for {
end = true
for i, elem := range *s {
for _, rmData := range rmItems {
if elem == rmData {
*s = slices.Delete(*s, i, i+1)
end = false
break
}
}
if !end {
break
}
}
if end {
break
}
}
}
func BenchmarkSliceRemoveFast(b *testing.B) {
slice := []int{1, 2, 3, 2, 3, 4}
for N := 0; N < b.N; N++ {
sliceRemove(&slice, 2, 3)
}
}
func BenchmarkSliceRemoveSlow(b *testing.B) {
slice := []int{1, 2, 3, 2, 3, 4}
for N := 0; N < b.N; N++ {
rmItems := []int{2, 3}
var newSlice []int
for _, e := range slice {
if !slices.Contains(rmItems, e) {
newSlice = append(newSlice, e)
}
}
}
}
go test -v -bench=BenchmarkSliceRemove -run=none -benchmem
BenchmarkSliceRemoveFast
BenchmarkSliceRemoveFast-8 123802942 9.264 ns/op 0 B/op 0 allocs/op
BenchmarkSliceRemoveSlow
BenchmarkSliceRemoveSlow-8 19463425 89.18 ns/op 24 B/op 2 allocs/op
Since Slice is backed by an array and since there is no way you can remove an element from an array and not reshuffle memory;and I did not want to do that ugly code; here is a pseudo code to keep an index for removed items; Basically I wanted an ordered slice where position mattered even after delete
type ListSlice struct {
sortedArray []int
deletedIndex map[int]bool
}
func lenSlice(m ListSlice)int{
return len(m.sortedArray)
}
func deleteSliceElem(index int,m ListSlice){
m.deletedIndex[index]=true
}
func getSliceElem(m ListSlice,i int)(int,bool){
_,deleted :=m.deletedIndex[i]
return m.sortedArray[i],deleted
}
for i := 0; i < lenSlice(sortedArray); i++ {
k,deleted := getSliceElem(sortedArray,i)
if deleted {continue}
....
deleteSliceElem(i,sortedArray)
}
m := ListSlice{sortedArray: []int{5, 4, 3},deletedIndex: make(map[int]bool) }
...
here is the playground example with pointers in it. https://play.golang.org/p/uNpTKeCt0sH
package main
import (
"fmt"
)
type t struct {
a int
b string
}
func (tt *t) String() string{
return fmt.Sprintf("[%d %s]", tt.a, tt.b)
}
func remove(slice []*t, i int) []*t {
copy(slice[i:], slice[i+1:])
return slice[:len(slice)-1]
}
func main() {
a := []*t{&t{1, "a"}, &t{2, "b"}, &t{3, "c"}, &t{4, "d"}, &t{5, "e"}, &t{6, "f"}}
k := a[3]
a = remove(a, 3)
fmt.Printf("%v || %v", a, k)
}
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