How to turn data from a txt file into an array of objects in Node

Question

I'm new to Node, and I have a text file that has data like this

Date    Open    High    Low Close   Volume
11-Jun-19   163.3   164.54  162.74  163.1   158470476
10-Jun-19   165.31  165.4   164.37  164.8   105667060
7-Jun-19    163.85  164.95  163.14  164.8   188337725 
...

I would like to create an array of objects like this

[{
    Date: "11-Jun-19",
    Open: 163.22,
    High: 164.28,
    Low: 163.05,
    Close: 163.88,
    Volume: 5854647
}, {
    Date: "12-Jun-19",
    Open: 163.22,
    High: 164.28,
    Low: 163.05,
    Close: 163.88,
    Volume: 5854647
}, {
    Date: "15-Jun-19",
    Open: 163.22,
    High: 164.28,
    Low: 163.05,
    Close: 163.88,
    Volume: 5854647
}]

How can I do this? This was my attempt:

const lineReader = require('line-reader');

lineReader.eachLine('input.txt', function (line) {
  let results = [];
  let divide = line.split("   ");
  for (let i = 0; i < divide.length; i++) {
    let field = divide[i].split("/t");
    results.push({
      date: field[0],
      open: field[1],
      high: field[2],
      low: field[3],
      close: field[4],
      volume: field[5]
    });
  }
  console.log(results);
});

But this create an array for each object and I get all the data showing under date like this:

[
  {
    date: '11-Jun-19\t163.3\t164.54\t162.74\t163.1\t158470476',
    open: undefined,
    high: undefined,
    low: undefined,
    close: undefined,
    volume: undefined
  }
]
[
  {
    date: '10-Jun-19\t165.31\t165.4\t164.37\t164.8\t105667060',
    open: undefined,
    high: undefined,
    low: undefined,
    close: undefined,
    volume: undefined
  }
]
...

You're splitting by "/t" not "\t". You could also split by any whitespace using /\s/ — Charlie Bamford
– Charlie Bamford, Commented Jul 20, 2021 at 16:39
Use regex to replace any consecutive whitespaces by a comma, then break into commas. — Elias Soares
– Elias Soares, Commented Jul 20, 2021 at 16:48

vsemozhebuty · Accepted Answer · 2021-07-20 17:07:30Z

You can try readline internal module, by the way (see this example), if your file is big and you do need line by line processing:

const fs = require('fs');
const readline = require('readline');

async function processLineByLine() {
  const fileStream = fs.createReadStream('test.txt');

  const rl = readline.createInterface({
    input: fileStream,
    crlfDelay: Infinity,
  });

  let headers = null;
  const data = [];

  for await (const line of rl) {
    const row = line.split(/\s+/);

    if (headers === null) { // So this is the first line.
      headers = row;
    } else {
      const entry = {};
      for (let i = 0; i < row.length; i++) {
        const header = headers[i];
        const cell = row[i];

        entry[header] = header === 'Date' ? cell : Number(cell);
        // Or more generally:
        // const mayBeNumber = Number(cell);
        // entry[header] = Number.isNaN(mayBeNumber) ? cell : mayBeNumber;
      }
      data.push(entry);
    }
  }

  console.log(data);
}

processLineByLine();

parastoo taleiniya · Accepted Answer · 2021-07-20 17:20:57Z

1

This code should work:

        const fs = require('fs');
    const file = fs.readFileSync('data.txt');
    //Read Each line separately and add them to an array. and remove first line of your file;
    const array = file.split('\n').slice(1);

    let objects = [], i, data;
    for(let row of array){
        i = 0;
        //separate each line data and add them to data array
        data = row.split(/ +/);
        objects.push({
            Date: data[i],
            Open: data[++i],
            High: data[++i],
            Low: data[++i],
            Close: data[++i],
            Volume:data[++i]
        })
    }

edited Jul 20, 2021 at 17:20

answered Jul 20, 2021 at 17:09

parastoo taleiniya

363 bronze badges

4 Comments

vsemozhebuty Over a year ago

It seems Date: data[i], shoud also be Date: data[i++],? Or the other lines should use preincrement.

parastoo taleiniya Over a year ago

@vsemozhebuty No, the Date value is in the first index of data array and the other lines should use increment

vsemozhebuty Over a year ago

Yes, but Date: data[i], and Open: data[i++], use the same i as it is incremented after returning its value (see Increment (++)).

parastoo taleiniya Over a year ago

I understood what does you mean and i edited my code. Thank you. @vsemozhebuty

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