How to remove duplicates in an interface array - go

Question

Lets say the input can contain string or integer values
names = ["rahul", "rohit","srujan", "rahul"] --> output = ["rahul", "rohit","srujan"]
age=[12,18,12,21] --> output = [12,18,21]
we can make use of this function to filter duplicates
package main
import (
"fmt"
)
func unique(intSlice []int) []int {
keys := make(map[int]bool)
list := []int{}
for _, entry := range intSlice {
if _, value := keys[entry]; !value {
keys[entry] = true
list = append(list, entry)
}
}
return list
}
func main() {
intSlice := []int{1,5,3,6,9,9,4,2,3,1,5}
fmt.Println(intSlice)
uniqueSlice := unique(intSlice)
fmt.Println(uniqueSlice)
}
This works only if the input is either string or integer but not both
How to make sure this function works for array interface

Answer 1

Use the reflect package to write a function that works with any slice type:
func unique(src interface{}) interface{} {
srcv := reflect.ValueOf(src)
dstv := reflect.MakeSlice(srcv.Type(), 0, 0)
visited := make(map[interface{}]struct{})
for i := 0; i < srcv.Len(); i++ {
elemv := srcv.Index(i)
if _, ok := visited[elemv.Interface()]; ok {
continue
}
visited[elemv.Interface()] = struct{}{}
dstv = reflect.Append(dstv, elemv)
}
return dstv.Interface()
}
Use it like this:
uniqueIntSlice := unique(intSlice).([]int)
Run the code on the Go Playground.

Answer 2

How to make sure this function works for a (unsorted) slice of empty interface{}
Considered that empty interface{} are comparable (https://stackoverflow.com/a/54003329/4466350)
Thus, to answer your question, it is very simple to rewrite your original code
package main
import (
"fmt"
)
func main() {
intSlice := []interface{}{1, 5, 3, 6, 9, 9, 4, 2, 3, 1, 5}
fmt.Println(unique(intSlice))
}
func unique(src []interface{}) []interface{} {
keys := make(map[interface{}]bool)
list := []interface{}{}
for _, entry := range src {
if _, value := keys[entry]; !value {
keys[entry] = true
list = append(list, entry)
}
}
return list
}
https://play.golang.org/p/vW7vgwz9yc1
If your question become, how to remove duplicates of any slice type, please check this other answer https://stackoverflow.com/a/65191679/4466350

Answer 3

Nothing elegant and very prone to errors, but you can us a function that receives two interface{} arguments, the first one is the slice to filter and the second is a pointer to the filtered slice, obviously if the first parameter is a slice of int, the second one MUST be s pointer to slice of int.
Inside the function you can check for the types of the parameters and treat them separately.
package main
import (
"fmt"
)
func unique(slice interface{}, filtered interface{}) error {
// Check for slice of string
if sliceOfString, ok := slice.([]string); ok {
// If slice is slice of string filtered MUST also be slice of string
filteredAsSliceOfString, ok := filtered.(*[]string)
if !ok {
return fmt.Errorf("filtered should be of type %T, got %T instead", &[]string{}, filtered)
}
keys := make(map[string]bool)
for _, entry := range sliceOfString {
if _, value := keys[entry]; !value {
keys[entry] = true
*filteredAsSliceOfString = append(*filteredAsSliceOfString, entry)
}
}
}else if sliceOfInt, ok := slice.([]int); ok {
// If slice is slice of int filtered MUST also be slice of int
filteredAsInt, ok := filtered.(*[]int)
if !ok {
return fmt.Errorf("filtered should be of type %T, got %T instead", &[]string{}, filtered)
}
keys := make(map[int]bool)
for _, entry := range sliceOfInt {
if _, value := keys[entry]; !value {
keys[entry] = true
*filteredAsInt = append(*filteredAsInt, entry)
}
}
} else {
return fmt.Errorf("only slice of in or slice of string is supported")
}
return nil
}
func main() {
intSlice := []int{1,5,3,6,9,9,4,2,3,1,5}
intSliceFiltered := make([]int, 0)
stringSlice := []string{"a", "b", "b", "c", "c", "c", "d"}
stringSliceFiltered := make([]string, 0)
fmt.Println(intSlice)
err := unique(intSlice, &intSliceFiltered) // Very important to send pointer in second parameter
if err != nil {
fmt.Printf("error filtering int slice: %v\n", err)
}
fmt.Println(intSliceFiltered)
fmt.Println(stringSlice)
err = unique(stringSlice, &stringSliceFiltered) // Very important to send pointer in second parameter
if err != nil {
fmt.Printf("error filtering string slice: %v\n", err)
}
fmt.Println(stringSliceFiltered)
}
As I said, it's not elegant. I haven't check this for errors.
Here it is running.