othersolution.js

'use strict';

const fs = require('fs');
const readline = require('readline');
const { performance: perf } = require('perf_hooks');

/**
 * Finds the largest value of all fields in `obj`
 * and returns its field name (key).
 */
function maxEntry(obj) {
  let maxValue = 0;
  let maxKey = null;
  for (let key of Object.keys(obj)) {
    if (obj[key] > maxValue) {
      maxKey = key;
      maxValue = obj[key];
    }
  }
  return maxKey;
}

function getFirstName(name) {
  // this code copied verbatim from [Paige Niedringhaus](https://github.com/paigen11/file-read-challenge/blob/master/readFileStream.js)
  let firstHalfOfName = name.split(', ')[1];
  if (firstHalfOfName !== undefined) {
    firstHalfOfName.trim();
    // filter out middle initials
    if (firstHalfOfName.includes(' ') && firstHalfOfName !== ' ') {
      let firstName = firstHalfOfName.split(' ')[0];
      return firstName.trim();
    } else {
      return firstHalfOfName;
    }
  }
}

function getFirstNameRegEx(name) {
  // idea for this taken from [Stuart Marks](https://stuartmarks.wordpress.com/2019/01/11/processing-large-files-in-java/)
  // the documentation assures me that a regex in this form is compiled at parse-time
  // and is indeed a constant in memory.
  const regex = /, (\S+)/;
  const match = regex.exec(name);
  return match && match[1];
}

const numberFormat4 = new Intl.NumberFormat('en-us', {
  maximumSignificantDigits: 4,
});
const numberFormatFull = new Intl.NumberFormat('en-us');

function main(args) {
  console.log(`Opening file '${args[0]}'.`);
  const rl = readline.createInterface({
    input: fs.createReadStream(args[0]),
    crlfDelay: Infinity,
  });

  const timeStartReadLoop = perf.now();
  let timeInsideReadLoop = 0;

  const nameCounts = {};
  let lineCount = 0;
  rl.on('line', line => {
    const timeStartInside = perf.now();
    lineCount++;
    const fields = line.split('|');
    const date = fields[4];
    const name = getFirstNameRegEx(fields[7]); // to count full names, just use `fields[7];`
    nameCounts[name] = (nameCounts[name] || 0) + 1;
    console.log(nameCounts);
    timeInsideReadLoop += perf.now() - timeStartInside;
  });

  rl.on('close', function() {
    const totalTime = numberFormat4.format(perf.now() - timeStartReadLoop);
    const insideTime = numberFormat4.format(timeInsideReadLoop);
    console.log(`Total time for reading and processing file: ${totalTime}ms.`);
    console.log(
      `Thereof time spent in custom processing code: ${insideTime}ms.`,
    );

    console.log(`Dataset has ${numberFormatFull.format(lineCount)} entries.`);

    const numUniqueNames = numberFormatFull.format(
      Object.keys(nameCounts).length,
    );
    console.log(`${numUniqueNames} different names found in file.`);

    const name = maxEntry(nameCounts);
    const nameOccurrences = numberFormatFull.format(nameCounts[name]);
    console.log(
      `The most common name is '${name}' with ${nameOccurrences} occurrences.`,
    );
  });

  console.log(`Getting started...`);
}

// note that in older versions of node, you need to `.splice(process.execArgv.length + 2)`
// but my v10.15 seems to already remove the runtime's arguments from the program's.
main(process.argv.splice(2));