# How to get intersection of two slice in golang?

## Issue

Is there any efficient way to get intersection of two slices in Go?

I want to avoid nested for loop like solution

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

intersection(slice1, slice2)
=> ["foo", "bar"]
``````

order of string does not matter

## Solution

Yes there are a few different ways to go about it.. Here’s an example that can be optimized.

``````package main

import "fmt"

func intersection(a []string, b []string) (inter []string) {
// interacting on the smallest list first can potentailly be faster...but not by much, worse case is the same
low, high := a, b
if len(a) > len(b) {
low = b
high = a
}

done := false
for i, l := range low {
for j, h := range high {
// get future index values
f1 := i + 1
f2 := j + 1
if l == h {
inter = append(inter, h)
if f1 < len(low) && f2 < len(high) {
// if the future values aren't the same then that's the end of the intersection
if low[f1] != high[f2] {
done = true
}
}
// we don't want to interate on the entire list everytime, so remove the parts we already looped on will make it faster each pass
high = high[:j+copy(high[j:], high[j+1:])]
break
}
}
// nothing in the future so we are done
if done {
break
}
}
return
}

func main() {
slice1 := []string{"foo", "bar", "hello", "bar"}
slice2 := []string{"foo", "bar"}
fmt.Printf("%+v\n", intersection(slice1, slice2))
}
``````

Now the intersection method defined above will only operate on `slices` of `strings`, like your example.. You can in theory create a definition that looks like this `func intersection(a []interface, b []interface) (inter []interface)`, however you would be relying on reflection and type casting so that you can compare, which will add latency and make your code harder to read. It’s probably easier to maintain and read to write a separate function for each type you care about.

`func intersectionString(a []string, b []string) (inter []string)`,

`func intersectionInt(a []int, b []int) (inter []int)`,

`func intersectionFloat64(a []Float64, b []Float64) (inter []Float64)`, ..ect

You can then create your own package and reuse once you settle how you want to implement it.

``````package intersection

func String(a []string, b []string) (inter []string)

func Int(a []int, b []int) (inter []int)

func Float64(a []Float64, b []Float64) (inter []Float64)
``````