Reservoir Sampling - algorithm from wiki (http://en.wikipedia.org/wiki/Reservoir_sampling)

reservoir_sampling.go

package main

import (
  "time"
  "math/rand"
  "fmt"
)
func randInt(min int, max int) int {
    return min + rand.Intn(max-min)
}

func main() {
  const SIZE = 10
  rand.Seed(time.Now().UTC().UnixNano())

  var sample []int // the reservoir
  largeSet := make([]int, 1000000) // holds the random large set
  for i := 0; i < 1000000; i++ { largeSet[i] = rand.Intn(100) }

  for index, value := range largeSet {
    // Generate the reservoir
    if (index < SIZE ){
      sample = append(sample, value)
    }else{
      // Randomly replace elements in the reservoir
      // with a decreasing probability.
      // Choose an integer between 0 and index (inclusive)
      r := randInt(0,index)
      if (r < SIZE) {
        sample[r] = value
      }
    }

  }
  fmt.Println(sample)
}