Ruby csv writing time ~34 seconds. Go csv writing time ~ 1.8 seconds.

go_write_csv.go

package main

import (
    "fmt"
    "time"
    "strconv"
    "os"
    "math/rand"
    "encoding/csv" 
)

const chars = "ABCDEFGHIJKLMNOP,  "

func gen_data(num_rows, num_cols int)  [][]string{
    data := make([][]string, num_rows)
    for i := range data {
        data[i] = make([]string, num_cols)
        for j := range data[i] {
            if j < (num_cols/2.0) {
                str := make([]uint8, 10)
                for s := range str {
                    str[s] = chars[rand.Intn(len(chars))]
                }
                data[i][j] = string(str[0:10])
            } else {
                data[i][j] = strconv.FormatFloat(rand.Float64() * 100.0, 'f', 10, 32)
            }
        }
    }
    return data
}

func write_csv(data [][]string) {
    f, err := os.Create("/tmp/go-out.csv")
    if err != nil {
        return
    }
    defer f.Close()
    out := csv.NewWriter(f)
    out.WriteAll(data)
}

func main() {
    data := gen_data(100000, 40)
    start := time.Now()
    write_csv(data)
    total := time.Since(start)
    fmt.Println(total)
}

ruby_write_csv.rb

require 'csv'


dt = [:str] * 20
dt += [:float] * 20

def time
  start = Time.now
  yield
  puts "Took #{Time.now - start}"
end

def gen_rows(data_types, rows)
  charset = "ABCDEFGHIJKLMNOP,  ".split("")
  result = []
  rows.times do |i|
    row = []
    data_types.each do |dt|
      case dt
      when :str
        row << (0...10).map{charset.sample}.join
      when :float
        row << (rand * 100).round(10)
      end
    end
    result << row
  end
  result
end

time do
  DATA = gen_rows(dt, 100000)
end

CSV.open("/tmp/foo.csv", "wb") do |csv|
  time do
    DATA.each do |row|
      csv << row
    end
  end
end