If I have
array1 := []int{1, 3, 4, 5}
array2 := []int{2, 4, 6, 8}
And I want to insert array2[2] i.e 6 at array1[1] i.e before 3 so that array1 becomes a slice of {1, 6, 3, 4, 5}. How can I do it?
Most the techniques I read online involve using the : operator but results in remaining elements being inserted as well. How can I append single values at an index in a slice?
Simple, efficient and logical way:
array1 has enough capacity (length) to accomodate the new, insertable element. To do that, append a single element using the builting append() (doesn't matter what that is, it'll get overwritten).copy() (elements you want to insert before).In code:
array1 := []int{1, 3, 4, 5}
array2 := []int{2, 4, 6, 8}
array1 = append(array1, 0) // Step 1
copy(array1[2:], array1[1:]) // Step 2
array1[1] = array2[2] // Step 3
fmt.Println(array1)
Output (try it on the Go Playground):
[1 6 3 4 5]
extending the answer from @Volker, i put the answer here https://play.golang.org/p/3Hla2y2ava too if you want to test it.
package main
import "fmt"
func main() {
array1 := []int{1, 3, 4, 5}
array2 := []int{2, 4, 6, 8}
temp := append([]int{array2[2]}, array1[1:]...)
array1 = append(array1[:1], temp...)
fmt.Println(array1)
}
I don't know is it optimal or not, but this piece of code works for me:
func sliceins(arr []int, pos int, elem int) []int { //insert element before pos in slice. if pos >= len(arr) insert into tail
if pos < 0 {
pos = 0
} else if pos >= len(arr) {
pos = len(arr)
}
out := make([]int, len(arr)+1)
copy(out[:pos], arr[:pos])
out[pos] = elem
copy(out[pos+1:], arr[pos:])
return out
}
In Your case just call
sliceins(array1, 1, array2[2])
I found the question setup pretty tricky to follow.
Rephrased, they want to insert an element. Here we have an array where it's missing the element 3 and we want to insert it.
package main
import (
"fmt"
)
func main() {
a := []int{1, 2, 4, 5, 6}
b := 3
// Make space in the array for a new element. You can assign it any value.
a = append(a, 0)
fmt.Println(a)
// Copy over elements sourced from index 2, into elements starting at index 3.
copy(a[3:], a[2:])
fmt.Println(a)
a[2] = b
fmt.Println(a)
}
Based on icza's post i wrote a function to shift the slice / array which I want to share with you:
package main
import "fmt"
func main() {
s := []string{"a", "c", "d"}
shiftArray(&s, 1, "b")
fmt.Println(s)
}
func shiftArray(array *[]string, position int, value string) {
// extend array by one
*array = append(*array, "")
// shift values
copy((*array)[position+1:], (*array)[position:])
// insert value
(*array)[position] = value
}