Modify CSV in Go

csv.go

package main

import (
	"bufio"
	"encoding/csv"
	"fmt"
	"io"
	"log"
	"os"
	"time"
)

func main() {
	filename := "infile.csv"
	fi, err := os.Open(filename)
	if err != nil {
		log.Fatalf("Error opening in file: %v", err)
	}
	defer fi.Close()

	fo, err := os.Create("outfile.csv")
	if err != nil {
		log.Fatalf("Error opening out file: %v", err)
	}
	defer fo.Close()

	reader := csv.NewReader(bufio.NewReader(fi))
	writer := csv.NewWriter(bufio.NewWriter(fo))

	lines := 0
	linelimit := 10
	flushCounter := 0
	flushLimit := 100

	m := make(map[string]string)
	m["StringToReplace1"] = "Test1"
	m["StringToReplace2"] = "Test2"

	tBefore := time.Now()
	for {
		line, error := reader.Read()
		if error == io.EOF {
			break
		} else if error != nil {
			log.Fatal(error)
		}

		// Replace cells.
		line = ReplaceIndex(line, 3, m)
		line = ReplaceIndex(line, 6, m)

		// Drop columns.
		line = RemoveIndex(line, 6)
		line = RemoveIndex(line, 10)

		writer.Write(line)

		// Flush based on value.
		flushCounter++
		if flushCounter == flushLimit {
			writer.Flush()
			flushCounter = 0
		}

		// Break based on value.
		lines++
		if lines == linelimit {
			break
		}
	}

	// Flush one last time.
	writer.Flush()

	fmt.Printf("Lines: %v\n", lines)
	fmt.Printf("Finished in: %v\n", time.Since(tBefore))
}

func RemoveIndex(s []string, index int) []string {
	return append(s[:index], s[index+1:]...)
}

func ReplaceIndex(s []string, index int, m map[string]string) []string {
	v := s[index]
	out := m[v]
	s[index] = out
	return s
}