javascript - Read lines of a txt file and organize in a JSON file - Stack Overflow

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I have a text file where each line is separated into 4 categories by colons and I want to put this into a JSON file, where each category is a value to the corresponding name in the JSON file.

Example data.txt file:

Date1:cat1:dog1:bug1
Date2:cat2:dog2:bug2
Date3:cat3:dog3:bug3

Example JSON file:

{
  "Date1": {
    "cat": "cat1",
    "dog": "dog1",
    "bug": "bug1"
  },
  "Date2": {
    "cat": "cat2",
    "dog": "dog2",
    "bug": "bug2"
    ...
  ...
}

I've never used JSON before but I think that's how to format it. How would I sort each line using the colons as markers for the next value and store it in the JSON file with the correct name using JavaScript and Node.js?

I have a text file where each line is separated into 4 categories by colons and I want to put this into a JSON file, where each category is a value to the corresponding name in the JSON file.

Example data.txt file:

Date1:cat1:dog1:bug1
Date2:cat2:dog2:bug2
Date3:cat3:dog3:bug3

Example JSON file:

{
  "Date1": {
    "cat": "cat1",
    "dog": "dog1",
    "bug": "bug1"
  },
  "Date2": {
    "cat": "cat2",
    "dog": "dog2",
    "bug": "bug2"
    ...
  ...
}

I've never used JSON before but I think that's how to format it. How would I sort each line using the colons as markers for the next value and store it in the JSON file with the correct name using JavaScript and Node.js?

• javascript
• json
• node.js
• fs

Share Improve this question Follow edited Aug 1, 2018 at 2:08 Rick 4,12499 gold badges2727 silver badges3737 bronze badges asked Jul 31, 2018 at 23:35 E tomE tom 11711 gold badge22 silver badges1010 bronze badges

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3 Answers 3

Sorted by: Reset to default 2

Use the csv package if you don't want to handle parsing csv file by yourself.

const fs = require("fs");
const csv = require("csv");

const result = {};
const keys = ["cat", "dog", "bug"]

// Read data
const readStream = fs.createReadStream("yourfile.txt");

// Parser
const parser = csv.parse({ delimiter: ":" });

parser.on("data", (chunk) => {
result[chunk[0]] = {};
    for(let i = 1; i < chunk.length; i ++) {
        result[chunk[0]][keys[i - 1]] = chunk[i];
    }
});

parser.on("end", () => {
    console.log(result);
});

readStream.pipe(parser);

If your JSON has this defined structure you can go about it with the following code:

import * as fs from 'fs';

/* If you have a large file this is a bad Idea, refer to reading from a stream 
 * From zhangjinzhou's answer
 */
const file = fs.readFileSync('path/to/data.txt', 'utf8');

const json = file.split(/\n|\r\n/).map(line => {
  const values = line.split(":");
  let obj = {}

  obj[values[0]] =  {
    cat: values[1],
    dog: values[2],
    bug: values[3],
  };

  return obj
}).reduce((acc, current) => Object.assign(acc, current), {})

Using RegExp and Array#forEach, convert the string to lines, then iterate over them and fill up the object with the corresponding data via:

const dataFileContent = 
`Date1:cat1:dog1:bug1
Date2:cat2:dog2:bug2
Date3:cat3:dog3:bug3`;

function processData(data) {
  // convert to lines
  const lines = data.match(/[^\r\n]+/g) || [];  
  const object = {};
  
  // iterate over the lines
  lines.forEach(line => {
    const parts = line.split(':');    
    const main = parts.shift();
    const pattern = /^(.*?)(\d+)$/;
    
    // create an object for each main part
    object[main] = {};    
    
    // fill each main part with the sub parts
    parts.forEach(part => {
      const match = part.match(pattern) || [];
      const key = match[1];
      const value = match[2];
            
      if (match) {
        object[main][key] = key + value;
      }
    });
  }); 
  
  return object;
}

const processedData = processData(dataFileContent);
console.log(processedData);

Then convert the processedData to JSON by using JSON.stringify and save it to a file via:

const fs = require('fs');

...
// processData
...

const json = JSON.stringify(processedData);
fs.writeFile('my_json_file.json', json, 'utf8');

For larger files, consider using Streams in Node.js as suggested by @zhangjinzhou.

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