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 costy.
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.
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]
}
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 9 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.
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.
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] }
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"
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 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
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] }
If it is not necessary to preserve the order, we can simply move the last element to the gap.
func remove(slice []int, i int) []int { slice[i] = slice[len(slice)-1] return slice[:len(slice)-1] }
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")
}
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 its not there yet
if i != len(s)-1 {
s[i] = s[len(s)-1]
}
// drop the last element
return s[:len(s)-1]
}
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)
}
