Go – Slice Find Index

In Go, finding the index of a specific element in a slice involves iterating through the slice and checking for the target element. Since Go does not provide a built-in function to find an index, you can achieve this functionality by implementing a custom function.

In this tutorial, we will explore how to find the index of an element in a slice with practical examples and detailed explanations.

Steps to Find Index in a Slice

  • Iterate Through Slice: Use a for loop with the range keyword to iterate through the slice.
  • Compare Elements: Compare each element with the target value.
  • Return Index: Return the index of the element if a match is found; otherwise, return a sentinel value like -1.

Examples of Finding Index in a Slice

1. Find Index of an Integer in a Slice

This example demonstrates how to find the index of an integer in a slice:

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package main

import "fmt"

// Function to find the index of an integer in a slice
func findIndex(slice []int, target int) int {
    for i, v := range slice {
        if v == target {
            return i
        }
    }
    return -1
}

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

    // Find the index of 30
    index := findIndex(numbers, 30)

    // Print the result
    fmt.Println("Index of 30:", index)
}

Explanation

  1. Define Function: The findIndex function iterates through the slice and compares each element with the target value.
  2. Return Index: If a match is found, the function returns the index of the element; otherwise, it returns -1.
  3. Call Function: The slice numbers and the target value 30 are passed to the function, and the index is printed.

Output

2. Find Index of a String in a Slice

This example demonstrates how to find the index of a string in a slice of strings:

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package main

import "fmt"

// Function to find the index of a string in a slice
func findStringIndex(slice []string, target string) int {
    for i, v := range slice {
        if v == target {
            return i
        }
    }
    return -1
}

func main() {
    // Declare and initialize a slice of strings
    fruits := []string{"apple", "banana", "cherry", "date"}

    // Find the index of "cherry"
    index := findStringIndex(fruits, "cherry")

    // Print the result
    fmt.Println("Index of 'cherry':", index)
}

Explanation

  1. Define Function: The findStringIndex function iterates through the slice and compares each string with the target value.
  2. Return Index: If a match is found, the function returns the index of the string; otherwise, it returns -1.
  3. Call Function: The slice fruits and the target string "cherry" are passed to the function, and the index is printed.

Output

3. Find Index of First Element Matching a Condition

This example demonstrates how to find the index of the first element that matches a custom condition:

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package main

import "fmt"

// Function to find the index of the first element greater than a threshold
func findIndexCondition(slice []int, condition func(int) bool) int {
    for i, v := range slice {
        if condition(v) {
            return i
        }
    }
    return -1
}

func main() {
    // Declare and initialize a slice of integers
    numbers := []int{5, 10, 15, 20, 25}

    // Find the index of the first number greater than 18
    index := findIndexCondition(numbers, func(n int) bool {
        return n > 18
    })

    // Print the result
    fmt.Println("Index of first element > 18:", index)
}

Explanation

  1. Define Function: The findIndexCondition function takes a slice and a custom condition function as input.
  2. Check Condition: The condition function determines whether each element satisfies the condition.
  3. Return Index: The function returns the index of the first element that satisfies the condition or -1 if no such element is found.
  4. Call Function: The slice numbers and a condition function checking for values greater than 18 are passed to the function, and the index is printed.

Output

Points to Remember

  • Custom Functions: Create custom functions to find indexes based on specific conditions.
  • Linear Search: Finding an index involves a linear search through the slice, which has a time complexity of O(n).
  • Handle Not Found: Return a sentinel value like -1 if the target element is not found in the slice.