Reading, manipulating, and writing arrays in JavaScript

manipulating-arrays.js

// runTests();

const fs = require("fs");

const fileOne = "../exports/someA.csv";
const fileTwo = "../exports/someB.csv";
const fileThree = "../exports/someC.csv";
const outputFile = "../exports/someOut.csv";

const arrayOne = readFile(fileOne);
const arrayTwo = readFile(fileTwo);
const arrayThree = readFile(fileThree);

const combined = combine(arrayOne, arrayTwo);
// const duplicates = getDuplicates(arrayOne, arrayTwo);
// const uniques = getUniques(arrayOne, arrayTwo);
// const subtracted = subtractArray(arrayTwo, arrayOne);

writeFile(outputFile, combined);

/*
    FUNCTIONS
*/

// Get everything in GroupA except GroupB items
function subtractArray(arrayOne, arrayTwo, silent) {
  const lookup = getArrayLookup(arrayTwo);
  const output = arrayOne.filter(value => typeof lookup[value] === "undefined");

  const shouldPrint = !silent;
  if (shouldPrint) {
    console.log(
      `✂️  Subtracted ${arrayTwo.length} users from ${arrayOne.length} and ended up with ${output.length}`
    );
  }
  return output;
}

// Get everything in GroupA OR GroupB
function combine(arrayOne, arrayTwo, silent) {
  const merged = [...arrayOne, ...arrayTwo];
  const uniques = [...new Set(merged)];

  const shouldPrint = !silent;
  if (shouldPrint) {
    console.log(
      `🌍 Combined the two files (${arrayOne.length} and ${arrayTwo.length} items) to get ${uniques.length} items`
    );
  }
  return uniques;
}

// Get everything in GroupA AND GroupB
function getDuplicates(arrayOne, arrayTwo, silent) {
  const lookup = getArrayLookup(arrayOne);
  const duplicates = arrayTwo.filter(item => !!lookup[item]);

  const shouldPrint = !silent;
  if (shouldPrint) {
    console.log(
      `💯  Compared ${arrayOne.length} vs ${arrayTwo.length} items and found ${duplicates.length} duplicates`
    );
  }
  return duplicates;
}

// Get everything in GroupA XOR GroupB
function getUniques(arrayOne, arrayTwo, silent) {
  const everything = combine(arrayOne, arrayTwo, true);
  const duplicates = getDuplicates(arrayOne, arrayTwo, true);
  const uniques = subtractArray(everything, duplicates, true);

  const shouldPrint = !silent;
  if (shouldPrint) {
    console.log(
      `🧬  Compared ${arrayOne.length} vs ${arrayTwo.length} items and found ${uniques.length} uniques`
    );
  }

  return uniques;

  // const lookup = getArrayLookup(arrayOne);
  // const uniques = arrayTwo.filter(item => !lookup[item]);
}

// Convert an array into a map of value => count
function getArrayLookup(array) {
  let lookup = {};

  array.forEach(item => {
    const exists = lookup[item] || 0;
    lookup[item] = exists + 1;
  });

  return lookup;
}

function readFile(path) {
  console.log("🤓  Reading file", path);
  return fs
    .readFileSync(path)
    .toString()
    .split("\n")
    .map(
      line =>
        line
          .trim() // remove white spaces from each line
          .split(",") // split into columns
          .map(e => e.trim()) // remove white spaces from each column
    )
    .map(line => line[0]) // get first column
    .filter(line => line);
}

function writeFile(path, array) {
  console.log("✍️  Writing file to", path);

  let writeStream = fs.createWriteStream(path);
  array.forEach(line => {
    writeStream.write(line + "\n");
  });
  writeStream.end();

  writeStream
    .on("finish", () => console.log(`🚀 Done! Wrote ${array.length} rows`))
    .on("error", error => console.error("🚨", error));
}

function compare(arr1, arr2) {
  if (arr1.length !== arr2.length) {
    return false;
  }

  return [...new Set(arr1.filter(el => arr2.includes(el)))];
}

function runTests() {
  const groupA = ["a", "b", "c", "d"];
  const groupB = ["c", "d", "e", "f"];

  const combined = combine(groupA, groupB); // expect a to f
  const duplicates = getDuplicates(groupA, groupB); // expect c, d
  const uniques = getUniques(groupA, groupB); // expect a, b, e, f
  const subtracted = subtractArray(groupA, groupB); // expect a, b

  console.log("");
  assert("combined", ["a", "b", "c", "d", "e", "f"], combined);
  assert("duplicates", ["c", "d"], duplicates);
  assert("uniques", ["a", "b", "e", "f"], uniques);
  assert("subtracted", ["a", "b"], subtracted);

  console.log("\n⚡️ Done. Quitting...");
  process.exit(0);
}

function assert(testName, expected, actual) {
  const pass = compare(expected, actual);

  if (pass) {
    console.log(`✓ Test passed: ${testName}`);
  } else {
    console.warn(`⨯ Test failed: ${testName}`);
    console.log("    Expected", expected, " but found ", actual);
  }

  return pass;
}