Golang slices.DeleteFunc Function

The slices.DeleteFunc function in Golang is part of the slices package, introduced in Go 1.21 as part of the standard library. This function allows you to remove elements from a slice based on a custom deletion function. It is particularly useful when you need to filter out elements that meet certain criteria, rather than just deleting by index.

Table of Contents

1. Introduction
2. slices.DeleteFunc Function Syntax
3. Examples
   • Basic Usage
   • Deleting Elements Based on Condition
   • Deleting Structs with Specific Field Values
4. Real-World Use Case Example
5. Conclusion

Introduction

The slices.DeleteFunc function provides a flexible way to delete elements from a slice by applying a custom function. This function is called for each element in the slice, and if it returns true, that element is removed. This makes it easy to clean up slices by removing unwanted elements based on complex conditions.

slices.DeleteFunc Function Syntax

The syntax for the slices.DeleteFunc function is as follows:

func DeleteFunc[S ~[]E, E any](s S, del func(E) bool) S

Parameters:

• s S: The slice from which you want to delete elements.
• del func(E) bool: A custom function that defines the condition for deleting elements. It should return true for elements that should be deleted.

Returns:

• S: A new slice with the elements that do not satisfy the deletion condition.

Behavior:

• Conditional deletion: The function iterates over the slice and applies the custom deletion function to each element. If the function returns true for an element, that element is removed from the resulting slice.

Examples

Basic Usage

This example demonstrates how to use slices.DeleteFunc to remove even numbers from a slice.

Example

package main

import (
	"fmt"
	"slices"
)

func main() {
	// Define a slice of integers
	numbers := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}

	// Define a custom function to delete even numbers
	deleteEven := func(n int) bool {
		return n%2 == 0
	}

	// Use slices.DeleteFunc to remove even numbers
	newSlice := slices.DeleteFunc(numbers, deleteEven)

	// Print the resulting slice
	fmt.Println("After deletion:", newSlice)
}

Output:

After deletion: [1 3 5 7 9]

Explanation:

• The slices.DeleteFunc function removes all even numbers from the numbers slice by applying the deleteEven function.

Deleting Elements Based on Condition

This example shows how to use slices.DeleteFunc to remove strings that are shorter than 5 characters from a slice.

Example

package main

import (
	"fmt"
	"slices"
)

func main() {
	// Define a slice of strings
	words := []string{"apple", "fig", "banana", "pear", "grape"}

	// Define a custom function to delete strings shorter than 5 characters
	deleteShort := func(s string) bool {
		return len(s) < 5
	}

	// Use slices.DeleteFunc to remove short strings
	newSlice := slices.DeleteFunc(words, deleteShort)

	// Print the resulting slice
	fmt.Println("After deletion:", newSlice)
}

Output:

After deletion: [apple banana grape]

Explanation:

• The slices.DeleteFunc function removes all strings that are shorter than 5 characters from the words slice by applying the deleteShort function.

Deleting Structs with Specific Field Values

This example demonstrates how slices.DeleteFunc can be used to remove structs from a slice based on specific field values.

Example

package main

import (
	"fmt"
	"slices"
)

type Person struct {
	Name string
	Age  int
}

func main() {
	// Define a slice of Person structs
	people := []Person{
		{"Alice", 30},
		{"Bob", 40},
		{"Charlie", 25},
		{"Dave", 40},
	}

	// Define a custom function to delete people who are 40 years old
	deleteAge40 := func(p Person) bool {
		return p.Age == 40
	}

	// Use slices.DeleteFunc to remove people who are 40 years old
	newSlice := slices.DeleteFunc(people, deleteAge40)

	// Print the resulting slice
	fmt.Println("After deletion:", newSlice)
}

Output:

After deletion: [{Alice 30} {Charlie 25}]

Explanation:

• The slices.DeleteFunc function removes all Person structs where Age is 40 by applying the deleteAge40 function, resulting in a slice with only those who are not 40 years old.

Real-World Use Case Example: Filtering Outdated Data

A practical use case for slices.DeleteFunc is filtering out outdated or irrelevant data from a list of records.

Example: Deleting Outdated Records

package main

import (
	"fmt"
	"time"
	"slices"
)

type Record struct {
	Name      string
	Timestamp time.Time
}

func main() {
	// Define a slice of records with timestamps
	records := []Record{
		{"Record1", time.Date(2023, 1, 1, 0, 0, 0, 0, time.UTC)},
		{"Record2", time.Date(2024, 1, 1, 0, 0, 0, 0, time.UTC)},
		{"Record3", time.Date(2022, 1, 1, 0, 0, 0, 0, time.UTC)},
	}

	// Define a custom function to delete records older than 2024
	deleteOutdated := func(r Record) bool {
		return r.Timestamp.Year() < 2024
	}

	// Use slices.DeleteFunc to remove outdated records
	newSlice := slices.DeleteFunc(records, deleteOutdated)

	// Print the resulting slice
	fmt.Println("After deletion:", newSlice)
}

Output:

After deletion: [{Record2 2024-01-01 00:00:00 +0000 UTC}]

Explanation:

• The slices.DeleteFunc function removes records with timestamps before the year 2024, leaving only the most recent data in the slice.

Conclusion

The slices.DeleteFunc function in Go is used for removing elements from slices based on custom conditions. It is particularly useful when dealing with complex types or when the criteria for deletion require custom logic. By using slices.DeleteFunc, you can efficiently manage and clean up your data in Go applications, ensuring that only the relevant elements remain in your slices.