Manipulating struct into csv in Golang

struct2csv.go

// stackoverflow post:
// https://stackoverflow.com/questions/75739563/converting-struct-to-csv-string/75740486#75740486
// [][]string or []Struct{} are preferred types to represent table data (csv) because of golang package ecosystem
// The case below is a special Data struct type that doesn't fit either
// which requires an additional step to transform it into [][]string before "encoding/csv" package can transform it into csv


package main

import (
	"encoding/csv"
	"log"
	"os"
	"strconv"
)

type Data struct {
	id   []string
	col1 []float64
	col2 []float64
}

func TransformDataTo2DSlice(d Data) [][]string {

	numRows := len(d.id)
	result := make([][]string, numRows+1)

	// Add header row
	result[0] = []string{"id", "col1", "col2"}

	// Add data rows
	for i := 0; i < numRows; i++ {
		result[i+1] = []string{d.id[i],
			strconv.FormatFloat(d.col1[i], 'f', -1, 64),
			strconv.FormatFloat(d.col2[i], 'f', -1, 64),
		}
	}

	return result
}

func main() {

	d := Data{
		id:   []string{"id_1", "id_1", "id_1", "id_1"},
		col1: []float64{340.384926, 321.385028, 520.341473, 500.385473},
		col2: []float64{123.285031, 4087.284675, -8958.284216, -7612.283668},
	}

	d2dslice := TransformDataTo2DSlice(d)

	// fmt.Printf("%+v", d2dslice)
	// [[id, col1, col2],
	//  [id_1, 340.384926, 123.285031],
	//  [id_1, 321.385028, 4087.284675],
	//  [id_1, 520.341473, -8958.284216],
	//  [id_1,500.385473,-7612.283668]]

	w := csv.NewWriter(os.Stdout)
	w.WriteAll(d2dslice)

	if err := w.Error(); err != nil {
		log.Fatalln("error writing csv:", err)
	}
     
        // stdout:
        // id,col1,col2
        // id_1,340.384926,123.285031
        // id_1,321.385028,4087.284675
        // id_1,520.341473,-8958.284216
        // id_1,500.385473,-7612.283668
}

To write csv into a string type variable instead:

   buf := new(bytes.Buffer)
    w := csv.NewWriter(buf)
    w.WriteAll(d2dslice)

    if err := w.Error(); err != nil {
        log.Fatalln("error writing csv:", err)
    }

    csvString := buf.String()

    fmt.Printf("%T\n", csvString)  // print the variable type
    // string

    fmt.Printf("%+v\n", csvString) // print the variable value
    // id,col1,col2
    // id_1,340.384926,123.285031
    // id_1,321.385028,4087.284675
    // id_1,520.341473,-8958.284216
    // id_1,500.385473,-7612.283668