在Golang中基于不同的切片过滤结构的切片

Question

In the example code below, I have a few users in manySimpleUsers that I would like to remove from manyFullUsers based on the Username.

If I do it with a nested couple of for... range loops, there will be many cycles required to filter all of the elements, especially when there are large numbers of elements in both Slices.

What is the best way to achieve this in Go?

package main

import "fmt"

func main() {
    fmt.Println("Hello, playground")

    type FullUser struct {
        UserName  string
        UserEmail string
    }

    manyFullUsers := []FullUser{{"foo", "[e-mail]"},
        {"bar", "[e-mail]"},
        {"baz", "[e-mail]"}}

    type SimpleUser struct {
        UserName string
    }

    manySimpleUsers := []SimpleUser{{"foo"}, {"bar"}}

    fmt.Println(manyFullUsers)
    fmt.Println(manySimpleUsers)
}

Answer 1

Create a map then use it to filter.

func filterByUserName(fu []FullUser, su []SimpleUser) (out []FullUser) {
    f := make(map[string]struct{}, len(su))
    for _, u := range su {
        f[u.UserName] = struct{}{}
    }
    for _, u := range fu {
        if _, ok := f[u.UserName]; ok {
            out = append(out, u)
        }
    }
    return
}

<kbd>playground</kbd>