Filtering composite types in a slice in Go

Filtering slices is a common operation in Go, especially when dealing with collections of data structures or composite types. In Go, a composite type is one that is made up of several types, such as structs, arrays, or slices themselves. This article will guide you through the process of filtering composite types specifically within a slice, starting from basic to more advanced examples.

Basic Example: Filtering a Slice of Integers

Before we dive into composite types, it’s helpful to understand how filtering works in simpler scenarios, like filtering a slice of integers. Filters remove elements that do not meet specific criteria, producing a new slice.

package main

import "fmt"

func main() {
    numbers := []int{1, 2, 3, 4, 5, 6}
    evenNumbers := filter(numbers, func(n int) bool {
        return n%2 == 0
    })
    fmt.Println(evenNumbers) // Output: [2, 4, 6]
}

func filter(nums []int, test func(int) bool) []int {
    var result []int
    for _, v := range nums {
        if test(v) {
            result = append(result, v)
        }
    }
    return result
}

Intermediate Example: Filtering a Slice of Structs

In real-world applications, data is often stored in custom structs. Here’s how to filter a slice of structs based on one or more struct fields.

package main

import "fmt"

type Person struct {
    Name string
    Age  int
}

func main() {
    people := []Person{
        {"Alice", 30},
        {"Bob", 25},
        {"Charlie", 35},
    }
    filteredPeople := filterPeople(people, func(p Person) bool {
        return p.Age > 30
    })
    fmt.Println(filteredPeople) // Output: [{Charlie 35}]
}

func filterPeople(people []Person, test func(Person) bool) []Person {
    var result []Person
    for _, p := range people {
        if test(p) {
            result = append(result, p)
        }
    }
    return result
}