Get all combinations of a given number of items from an array of int64 items (can type as per your requirement).

combinations.go

package main

import (
  "fmt"
  )

  func GetAllSubsets(arr []int64, size int) [][]int64{
    if len(arr) == size {
      result := [][]int64{arr}
      return result
    } else if len(arr) > size && size > 0 {
      sub_arr := arr[1:]
      first_element := arr[0]
      complete_subset_arr := GetAllSubsets(sub_arr, size)
      partial_subset_arr := GetAllSubsets(sub_arr, size-1)
      for _, i := range partial_subset_arr {
        if len(i) != 0 {
          new_slice := []int64{first_element}
          new_slice = append(new_slice, i...)
          complete_subset_arr = append(complete_subset_arr, new_slice)
        }
  		}
      if size == 1 {
        complete_subset_arr = append(complete_subset_arr, []int64{first_element})
      }
  		return complete_subset_arr
    } else {
      result := [][]int64{}
      return result
    }
  }

  func main() {
    arr := []int64{1,2,3,4,5}
    combinations := GetAllSubsets(arr, 4)
    for _, i := range combinations {
      fmt.Println("====",i)
    }
  }