Parsing CSV with common data preceding other data with NodeJS - node.js

Question

I'm trying to read in CSV files with nodejs and the code is like below.
fs.createReadStream(file)
.pipe(csv.parse({from_line: 6, columns: true, bom: true}, (err, data) => {
data.forEach((row, i) => {
As I am using from_line parameter, the data starts at line 6 with header.
The issue is that the line #3 has the date which is also used with other data.
What is the best way to resolve this?
Data file looks like below:
Genre: ABC
Date: 2020-01-01, 2020-12-31
Number of Data: 300
No., Code, Name, sales, delivery, return, stock
1, ......
2, ......
Additional question
I have inserted iconv.decodeStream　in the second part of function.
How could I apply the same decoder for header read-in process?
fs.createReadStream(file)
.pipe(iconv.decodeStream("utf-8"))
.pipe(csv.parse({from_line: 6, columns: true, bom: true}, (err, data) => {
data.forEach((row, i) => {

Answer 1

I'd suggest reading the header data first, then you can access this data in your processing callback(s), something like the example below:
app.js
// Import the package main module
const csv = require('csv')
const fs = require("fs");
const { promisify } = require('util');
const parse = promisify(csv.parse);
const iconv = require('iconv-lite');
async function readHeaderData(file, iconv) {
let buffer = Buffer.alloc(1024);
const fd = fs.openSync(file)
fs.readSync(fd, buffer);
fs.closeSync(fd);
buffer = await iconv.decode(buffer, "utf-8");
const options = { to_line: 3, delimiter: ':', columns: false, bom: true, trim: true };
const rows = await parse(buffer, options);
// Convert array to object
return Object.fromEntries(rows);
}
async function readFile(file, iconv) {
const header = await readHeaderData(file, iconv);
console.log("readFile: File header:", header);
fs.createReadStream(file)
.pipe(iconv.decodeStream("utf-8"))
.pipe(csv.parse({ from_line: 6, columns: true, bom: true, trim: true }, (err, data) => {
// We now have access to the header data along with the row data in the callback.
data.forEach((row, i) => console.log( { line: i, header, row } ))
}));
}
readFile('stream-with-skip.csv', iconv)
This will give an output like:
readFile: File header: {
Genre: 'ABC',
Date: '2020-01-01, 2020-12-31',
'Number of Data': '300'
}
and
{
line: 0,
header: {
Genre: 'ABC',
Date: '2020-01-01, 2020-12-31',
'Number of Data': '300'
},
row: {
'No.': '1',
Code: 'Code1',
Name: 'Name1',
sales: 'sales1',
delivery: 'delivery1',
return: 'return1',
stock: 'stock1'
}
}
{
line: 1,
header: {
Genre: 'ABC',
Date: '2020-01-01, 2020-12-31',
'Number of Data': '300'
},
row: {
'No.': '2',
Code: 'Code2',
Name: 'Name2',
sales: 'sales2',
delivery: 'delivery2',
return: 'return2',
stock: 'stock2'
}
}
example.csv
Genre: ABC
Date: 2020-01-01, 2020-12-31
Number of Data: 300
No., Code, Name, sales, delivery, return, stock
1, Code1, Name1, sales1, delivery1, return1, stock1
2, Code2, Name2, sales2, delivery2, return2, stock2