histogram.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"os"
	"strings"

	"github.com/pkg/errors"
)

func main() {
	ns, err := parseNumbers(os.Stdin)
	if err != nil {
		log.Fatalln(err)
	}

	min, max := minmax(ns)

	split := 10
	step := (max - min) / float32(split)

	buckets := make([]int, 0, split+1)
	for i := 0; i <= split; i++ {
		count := countWithin(ns, min+step*float32(i), min+step*float32(i+1))
		buckets = append(buckets, count)
	}

	maxCount := 0
	for _, count := range buckets {
		if count > maxCount {
			maxCount = count
		}
	}

	barSize := 30
	for i, count := range buckets {
		bar := strings.Repeat("=", barSize*count/maxCount)
		fmt.Printf("[%.2f, %.2f)\t%d\t%s\n", min+step*float32(i), min+step*float32(i+1), count, bar)
	}
}

func countWithin(ns []float32, min, max float32) int {
	count := 0
	for _, n := range ns {
		if n >= min && n < max {
			count++
		}
	}
	return count
}

func minmax(ns []float32) (float32, float32) {
	if len(ns) == 0 {
		return 0, 0
	}
	min, max := ns[0], ns[0]
	for _, n := range ns[1:] {
		if n < min {
			min = n
		}
		if n > max {
			max = n
		}
	}
	return min, max
}

func parseNumbers(r io.Reader) ([]float32, error) {
	ns := make([]float32, 0)
	var n float32
	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		fmt.Sscanf(scanner.Text(), "%f", &n)
		ns = append(ns, n)
	}
	if err := scanner.Err(); err != nil {
		return nil, errors.Wrapf(err, "could not scan")
	}
	return ns, nil
}