/
sample.go
185 lines (156 loc) · 3.76 KB
/
sample.go
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package main
import (
"bufio"
"flag"
"fmt"
"io"
"math/rand"
"os"
"strconv"
"strings"
"time"
)
var (
samplingProbability float64
reservoirSize uint
splitStr string
outputFilename string
)
func main() {
flag.Float64Var(&samplingProbability, "p", 0.0, "Sample lines at probability p in [0, 1].")
flag.UintVar(&reservoirSize, "r", 0, "Sample exactly k lines.")
flag.StringVar(&splitStr, "s", "", "Split the input into n random subsets. Delimit weights with commas, e.g. 8,1,1. Weights will be normalized to sum to 1.")
flag.StringVar(&outputFilename, "o", "", "Output file(s). If not specified, write to stdout. Required and used as a basename for splitting. The basename will be appended with _1, _2, etc.")
flag.Parse()
rand.Seed(time.Now().UnixNano())
if reservoirSize > 0 && samplingProbability > 0.0 {
fmt.Println("You can specify either -p or -r, but not both.")
flag.PrintDefaults()
return
}
input := inputReader(flag.Args())
if splitStr != "" {
if outputFilename == "" {
fmt.Println("To split input, you must specify an output base filename with -o.")
flag.PrintDefaults()
return
}
Split(input)
} else if samplingProbability > 0.0 {
sampleAtRate(input, samplingProbability, os.Stdout)
} else if reservoirSize > 0 {
lines := reservoirSample(input, reservoirSize)
for _, line := range lines {
fmt.Print(line)
}
}
}
func Split(input io.Reader) {
weights := parseSplitWeights()
bufReader := bufio.NewReader(input)
// Create a set of writers, one per output split.
writers := make(map[int]io.Writer, len(weights))
for i, _ := range weights {
outName := fmt.Sprintf("%s_%d", outputFilename, i)
file, err := os.Create(outName)
if err != nil {
panic(fmt.Sprintf("Couldn't open %s", outName))
}
defer file.Close()
writers[i] = bufio.NewWriter(file)
}
for {
line, err := bufReader.ReadBytes('\n')
if err != nil {
break
}
r := rand.Float64()
for i, w := range weights {
if r < w {
_, err := writers[i].Write(line)
if err != nil {
panic(fmt.Sprintf("Error %s writing to split %i", err, i)
}
}
}
}
return
}
func parseSplitWeights() (weights []float64) {
weights = make([]float64, 0)
sum := 0.0
for _, weightStr := range strings.Split(splitStr, ",") {
w, err := strconv.ParseFloat(weightStr, 64)
if err != nil {
panic(fmt.Sprintf("Bad weight string: %s", weightStr))
}
weights = append(weights, w)
sum += w
}
for i, w := range weights {
weights[i] = w / sum
}
return weights
}
func inputReader(args []string) (reader io.Reader) {
readers := make([]io.Reader, 0)
for _, arg := range args {
file, err := os.Open(arg)
//defer file.Close()
if arg == "-" {
readers = append(readers, os.Stdin)
}
if file != nil && err == nil {
readers = append(readers, file)
}
}
if len(readers) == 0 {
return os.Stdin
}
return io.MultiReader(readers...)
}
func sampleAtRate(reader io.Reader, rate float64, writer io.Writer) {
bufReader := bufio.NewReader(reader)
for {
line, err := bufReader.ReadBytes('\n')
if err != nil {
break
}
if rand.Float64() < rate {
writer.Write(line)
}
}
}
func reservoirSample(reader io.Reader, k uint) (reservoir []string) {
reservoir = make([]string, k)
bufReader := bufio.NewReader(reader)
var n uint = 0
for {
n++
line, err := bufReader.ReadString('\n')
if err != nil {
break
}
if n <= k {
reservoir[n-1] = line
// Replace a random element with probability k/n
} else if rand.Float64() < float64(k)/float64(n) {
reservoir[rand.Intn(int(k))] = line
}
}
return reservoir
}
func lineCount(reader io.Reader) (count uint) {
count = 0
bufReader := bufio.NewReader(reader)
for {
c, err := bufReader.ReadByte()
if err != nil {
return
}
if c == '\n' {
count++
}
}
return
}