How to find the difference between two slices of strings in Golang?

Here is my desired outcome

slice1 := []string{"foo", "bar","hello"}
slice2 := []string{"foo", "bar"}

difference(slice1, slice2)
=> ["hello"]

I am looking for the difference between the two string slices!

Depending on the size of the slices, different solutions might be best.

My answer assumes order doesn't matter.

Using simple loops, only to be used with smaller slices:

package main

import "fmt"

func difference(slice1 []string, slice2 []string) []string {
    var diff []string

    // Loop two times, first to find slice1 strings not in slice2,
    // second loop to find slice2 strings not in slice1
    for i := 0; i < 2; i++ {
        for _, s1 := range slice1 {
            found := false
            for _, s2 := range slice2 {
                if s1 == s2 {
                    found = true
                    break
                }
            }
            // String not found. We add it to return slice
            if !found {
                diff = append(diff, s1)
            }
        }
        // Swap the slices, only if it was the first loop
        if i == 0 {
            slice1, slice2 = slice2, slice1
        }
    }

    return diff
}

func main() {
    slice1 := []string{"foo", "bar", "hello"}
    slice2 := []string{"foo", "world", "bar", "foo"}

    fmt.Printf("%+v\n", difference(slice1, slice2))
}

Output:

[hello world]

Playground: http://play.golang.org/p/KHTmJcR4rg