Converting dynamic JSON to CSV in Golang

Question

I tried to convert dynamic JSON to CSV, I investigate libs and answers I can't find a remarkable thing.

This and this examples could be helpful but I can't add the JSON's struct to my code, JSON is dynamic.

In Python & JS, I saw these examples;

Python;

# Python program to convert
# JSON file to CSV
 
 
import json
import csv
 
 
# Opening JSON file and loading the data
# into the variable data
with open('data.json') as json_file:
    data = json.load(json_file)
 
employee_data = data['emp_details']
 
# now we will open a file for writing
data_file = open('data_file.csv', 'w')
 
# create the csv writer object
csv_writer = csv.writer(data_file)
 
# Counter variable used for writing
# headers to the CSV file
count = 0
 
for emp in employee_data:
    if count == 0:
 
        # Writing headers of CSV file
        header = emp.keys()
        csv_writer.writerow(header)
        count += 1
 
    # Writing data of CSV file
    csv_writer.writerow(emp.values())
 
data_file.close()

JS;

const items = json3.items
const replacer = (key, value) => value === null ? '' : value // specify how you want to handle null values here
const header = Object.keys(items[0])
const csv = [
  header.join(','), // header row first
  ...items.map(row => header.map(fieldName => JSON.stringify(row[fieldName], replacer)).join(','))
].join('\r\n')

console.log(csv)

These codes help convert dynamic JSON to CSV easily.

Example input & output;

JSON(input);

[
  {
    "name": "John",
    "age": "21"
  },
  {
    "name": "Noah",
    "age": "23"
  },
  {
    "name": "Justin",
    "age": "25"
  }
]

CSV(output);

"name","age"
"John","21"
"Noah","23"
"Justi","25"

So how can I convert dynamic JSON to CSV in Go?

PS: I discover a Golang lib(json2csv) that helps to convert but only works on command prompt.

I few online tools for example;

https://csvjson.com/json2csv

https://data.page/json/csv

json2csv is a library (as you mentioned), not just a command line tool. — Jonathan Hall
– Jonathan Hall, Commented Aug 10, 2022 at 8:38
How does your input look like? Is it a JSON array of dynamic, but identical JSON objects? Or elements may be completely independent? Please be more specific in what you want, provide example input and output at least. — icza
– icza, Commented Aug 10, 2022 at 9:36
For an example check out their cmd main file. But for your simple example I would just implement it by hand and not depend on another library. — icza
– icza, Commented Aug 10, 2022 at 10:36

ORHAN ERDAY · Accepted Answer · 2022-08-11 17:29:59Z

After investigation, I handle it with yukithm/json2csv package.

package main

import (
    "bytes"
    "encoding/json"
    "github.com/yukithm/json2csv"
    "log"
    "os"
)

func main() {
    b := &bytes.Buffer{}
    wr := json2csv.NewCSVWriter(b)
    j, _ := os.ReadFile("your-input-path\\input.json")
    var x []map[string]interface{}

    // unMarshall json
    err := json.Unmarshal(j, &x)
    if err != nil {
        log.Fatal(err)
    }

    // convert json to CSV
    csv, err := json2csv.JSON2CSV(x)
    if err != nil {
        log.Fatal(err)
    }

    // CSV bytes convert & writing...
    err = wr.WriteCSV(csv)
    if err != nil {
        log.Fatal(err)
    }
    wr.Flush()
    got := b.String()

    //Following line prints CSV
    println(got)

    // create file and append if you want
    createFileAppendText("output.csv", got)
}

//
func createFileAppendText(filename string, text string) {
    f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
    if err != nil {
        panic(err)
    }

    defer f.Close()

    if _, err = f.WriteString(text); err != nil {
        panic(err)
    }
}

input.json;

[
  {
    "Name": "Japan",
    "Capital": "Tokyo",
    "Continent": "Asia"
  },
  {
    "Name": "Germany",
    "Capital": "Berlin",
    "Continent": "Europe"
  },
  {
    "Name": "Turkey",
    "Capital": "Ankara",
    "Continent": "Europe"
  },
  {
    "Name": "Greece",
    "Capital": "Athens",
    "Continent": "Europe"
  },
  {
    "Name": "Israel",
    "Capital": "Jerusalem",
    "Continent": "Asia"
  }
]

output.csv

/Capital,/Continent,/Name
Tokyo,Asia,Japan
Berlin,Europe,Germany
Ankara,Europe,Turkey
Athens,Europe,Greece
Jerusalem,Asia,Israel

p1gd0g · Accepted Answer · 2022-08-10 11:42:52Z

0

Paste this to https://github.com/yukithm/json2csv/blob/master/cmd/json2csv/main.go and insert the func to main.

func stackoverflow() {

    jsonStr := `
[
  {
    "name": "John",
    "age": "21"
  },
  {
    "name": "Noah",
    "age": "23"
  },
  {
    "name": "Justin",
    "age": "25"
  }
]`

    buff := bytes.NewBufferString(jsonStr)

    data, _ := readJSON(buff)

    results, _ := json2csv.JSON2CSV(data)

    headerStyle := headerStyleTable["jsonpointer"]
    err := printCSV(os.Stdout, results, headerStyle, false)
    if err != nil {
        log.Fatal(err)
    }
}

It works for me.

➜  json2csv git:(master) ✗ go run main.go 
/age,/name
21,John
23,Noah
25,Justin

answered Aug 10, 2022 at 11:42

p1gd0g

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