Read from nth row in csv typescript

Question

I am trying to read a csv file from 4th row, in my csv file first 3 rows contains some meta data in column1. But the actual number of columns in csv is 6.

eg:

metadata1
metadata2
metadata3
head01,head02,head03,head04,head05,head06
data11,data12,data13,data14,data15,data16
data21,data22,data23,data24,data25,data26

Code I am trying is:

fs.createReadStream('/path/file.csv').pipe(
        parse({ from_line: 4, fromLine: 4 }, function(data, err) {
        console.log(data);
    })
);

I am getting data as undefined. Also If I am removing the args of parse, I am getting error Error: Invalid Record Length: expect 1, got 6 on line 4. Please guide!

Temunel · Accepted Answer · 2024-09-11 05:55:24Z

1

First, Error: Invalid Record Length: expect 1, got 6 on line 4 is because parse function expects the number of columns to be consistent throughout the file. The metadata lines have only 1 column, while the data lines have 6 columns, which is causing the parser to expect only 1 column when reading the 4th line.

So, You were right to skip the first three lines before passing the stream to the parser. ({ from_line: 4 })

But the problem is that you're using the callback API incorrectly.

The signature is parse(data, [options], callback). It takes the CSV in the 1st argument, options in the 2nd argument, and a user callback in the 3rd argument. The callback receives any error thrown by the CSV parser in the first parameter (err), or an array of records in the second argument(data). It returns an array.

So, this is the corrected code.

const fs = require('fs'); 
const { parse } = require('csv-parse');

fs.createReadStream('/path/file.csv').pipe(
  parse({ from_line: 4 }, function(err, data) {
    console.log(data);
  })
);

FYI, this is the example of the Promises usage.

fs.createReadStream('/path/file.csv')
  .pipe(parse({ from_line: 4 }))
  .on('data', (data) => {
    console.log(data);
  })
  .on('error', (err) => {
    console.error(err.message);
  });

I hope this solves your issue.

edited Sep 11, 2024 at 5:55

answered Aug 27, 2024 at 11:17

Temunel

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2 Comments

Shashi Ranjan Over a year ago

This solution works after adding import { parse } from "csv-parse";

Temunel Over a year ago

yes, you need to import fs and csv-parse. const fs = require('fs'); const { parse } = require('csv-parse');

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