Go Slice – Insert Element

In Go, slices are dynamic and allow elements to be added or removed. However, inserting an element at a specific position in a slice requires manually creating a new slice to accommodate the new element. Go does not have a built-in function for slice insertion, but you can achieve this functionality with custom logic.

In this tutorial, we will explore how to insert an element into a slice at a specific index with practical examples and detailed explanations.

Steps to Insert an Element in a Slice

Validate the Index: Ensure the insertion index is within the valid range of the slice.
Split the Slice: Use slicing to split the original slice into two parts: before and after the insertion point.
Append the Element: Insert the new element by combining the two parts with the new element in between.

Examples of Slice Element Insertion

1. Insert an Element at a Specific Index

This example demonstrates how to insert an element at a specific index in a slice:

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package main

import "fmt"

// Function to insert an element at a specific index in a slice
func insertElement(slice []int, index int, value int) []int {
    if index < 0 || index > len(slice) {
        fmt.Println("Invalid index")
        return slice
    }
    // Insert the element
    return append(slice[:index], append([]int{value}, slice[index:]...)...)
}

func main() {
    // Declare and initialize a slice
    numbers := []int{10, 20, 30, 40, 50}

    // Insert 25 at index 2
    updatedSlice := insertElement(numbers, 2, 25)

    // Print the updated slice
    fmt.Println("Updated Slice:", updatedSlice)
}

Explanation

Define Function: The insertElement function checks if the index is valid and uses slicing to insert the new element at the specified position.
Split Slice: The slice is split into two parts using slice[:index] and slice[index:].
Insert Element: The new element is inserted by appending it to the first part and then appending the second part.
Print Result: The updated slice is printed in the main function.

Output

2. Insert an Element at the Beginning of a Slice

This example demonstrates how to insert an element at the beginning of a slice:

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package main

import "fmt"

func main() {
    // Declare and initialize a slice
    numbers := []int{10, 20, 30, 40, 50}

    // Insert 5 at the beginning
    updatedSlice := append([]int{5}, numbers...)

    // Print the updated slice
    fmt.Println("Updated Slice:", updatedSlice)
}

Explanation

Insert at Beginning: A new slice with the element 5 is created and concatenated with the original slice using append.
Updated Slice: The resulting slice includes 5 as the first element, followed by the original elements.

Output

3. Insert an Element at the End of a Slice

This example demonstrates how to insert an element at the end of a slice:

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package main

import "fmt"

func main() {
    // Declare and initialize a slice
    numbers := []int{10, 20, 30, 40, 50}

    // Insert 60 at the end
    updatedSlice := append(numbers, 60)

    // Print the updated slice
    fmt.Println("Updated Slice:", updatedSlice)
}

Explanation

Insert at End: The element 60 is appended to the original slice using append.
Updated Slice: The resulting slice includes 60 as the last element.

Output

Points to Remember

Valid Index: Ensure the index is within the range [0, len(slice)] to avoid errors.
Dynamic Slices: Use append for efficient slice operations.
Memory Allocation: Inserting elements may involve reallocating memory if the capacity of the slice is exceeded.

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How to Insert Element in Slice in Go