/
r3.go
89 lines (79 loc) · 1.63 KB
/
r3.go
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// r3: parse temperatures manually instead of using strconv.ParseFloat
//
// ~517ms for 10M rows (1.94x as fast as r1)
package main
import (
"bufio"
"bytes"
"fmt"
"io"
"os"
"sort"
)
func r3(inputPath string, output io.Writer) error {
type stats struct {
min, max, sum float64
count int64
}
f, err := os.Open(inputPath)
if err != nil {
return err
}
defer f.Close()
stationStats := make(map[string]*stats)
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := scanner.Bytes()
station, tempBytes, hasSemi := bytes.Cut(line, []byte(";"))
if !hasSemi {
continue
}
negative := false
index := 0
if tempBytes[index] == '-' {
index++
negative = true
}
temp := float64(tempBytes[index] - '0')
index++
if tempBytes[index] != '.' {
temp = temp*10 + float64(tempBytes[index]-'0')
index++
}
index++ // skip '.'
temp += float64(tempBytes[index]-'0') / 10
if negative {
temp = -temp
}
s := stationStats[string(station)]
if s == nil {
stationStats[string(station)] = &stats{
min: temp,
max: temp,
sum: temp,
count: 1,
}
} else {
s.min = min(s.min, temp)
s.max = max(s.max, temp)
s.sum += temp
s.count++
}
}
stations := make([]string, 0, len(stationStats))
for station := range stationStats {
stations = append(stations, station)
}
sort.Strings(stations)
fmt.Fprint(output, "{")
for i, station := range stations {
if i > 0 {
fmt.Fprint(output, ", ")
}
s := stationStats[station]
mean := s.sum / float64(s.count)
fmt.Fprintf(output, "%s=%.1f/%.1f/%.1f", station, s.min, mean, s.max)
}
fmt.Fprint(output, "}\n")
return nil
}