Remove duplicate emails from a csv and output the result to a new one.

csv_strip_dupes.go

package main

import (
	"encoding/csv"
	"fmt"
	"os"
	"strings"
)

func main() {
	f, err := os.OpenFile("interest_2.csv", os.O_RDONLY, 0644)
	if err != nil {
		panic(err)
	}
	defer f.Close()

	r := csv.NewReader(f)
	records, err := r.ReadAll()
	if err != nil {
		panic(err)
	}

	recordMap := make(map[string]struct{})
	var rto [][]string

	for idx, er := range records {
		if idx == 0 {
			continue
		}
		username := er[0]
		email := strings.ToLower(er[1])

		if _, ok := recordMap[email]; ok {
			continue
		}
		rto = append(rto, []string{username, email})
		recordMap[email] = struct{}{}
	}

	f2, err := os.Create("output.csv")
	if err != nil {
		panic(err)
	}
	defer f2.Close()
	err = csv.NewWriter(f2).WriteAll(rto)
	if err != nil {
		panic(err)
	}

	fmt.Printf("We've got %d unique records.\n", len(recordMap))
	// fmt.Println("Hello, world!", len(rec))
}