How to Insert an Element into a Go Slice at a Specific Index?

Inserting a Value into a Slice at a Specified Index

Problem:

Given two slices, array1 and array2, you want to insert an element from array2 into array1 at a specific index, shifting the subsequent elements in array1 accordingly. For example, you want to insert array2[2] (6) into array1[1] (before 3), resulting in [1, 6, 3, 4, 5]. How can you achieve this?

Solution:

Inserting values into slices in Go can be accomplished in several ways.

Using the Slices Package (Go 1.21 ):

result := slices.Insert(slice, index, value)

Note that the index must be within the valid range (0 to the length of the slice). This method avoids the need to manually shift elements.

Using Append and Assignment:

a = append(a[:index+1], a[index:]...)
a[index] = value

This solution involves using append to create a new slice containing the first index elements of the original slice followed by the element to insert and the remaining elements from index onward. Then, the value at the desired index is assigned to the new value.

Using a Single For Loop:

for i := len(a); i > index; i-- {
    a[i] = a[i-1]
}
a[index] = value

This method iterates over the slice, shifting each element one position to the right from its original index until the insertion point is reached. The value to insert is then assigned at the specified index.

Choosing the Right Approach:

Depending on the requirements and performance considerations, you can select the most appropriate approach for inserting values into slices in Go. The slices package, available in Go 1.21 , provides an efficient and straightforward solution with built-in error handling. However, for simpler scenarios or when using older Go versions, the other methods offer flexibility and performance optimization options.

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