Reduce Data with Javascript Array

javascript_reduce.js

// 1. Transform an Array into a Single Value using Reduce
var data = [15, 3, 20];

var reducer = function(accumulator, item) {
  return accumulator + item;
};

var initialValue = 0;

var total = data.reduce(reducer, initialValue);

console.log("The sum is: ", total);

// 2. Reduce an Array into a Single Object
//see CONSOLE!
var votes = [
  "angular",
  "angular",
  "react",
  "react",
  "react",
  "angular",
  "ember",
  "react",
  "vanilla"
];

var initialValue = {};

var reducer = function(tally, vote) {
  if (!tally[vote]) {
    tally[vote] = 1;
  } else {
    tally[vote] = tally[vote] + 1;
  }

  return tally;
};

var result = votes.reduce(reducer, initialValue);

// Output
console.log("Angular: ", result.angular)
console.log("React: ", result.react)
console.log("Ember: ", result.ember)
console.log("Vanilla: ", result.vanilla)

// 3. Use Reduce to Filter and Map over Large Datasets
var data = [1, 2, 3];
var doubled = data.reduce(function(acc, value) {
  acc.push(value * 2);

  return acc;
}, []);

var doubleMapped = data.map(function(item) {
  return item * 2;
});

var data2 = [1, 2, 3, 4, 5, 6];
var evens = data2.reduce(function(acc, value) {
  if (value % 2 === 0) {
    acc.push(value);
  }

  return acc;
}, []);

var evenFiltered = data2.filter(function(item) {
  return (item % 2 === 0);
});

var filterMapped = data2.filter(function(value) {
  return value % 2 === 0;
}).map(function(value) {
  return value * 2;
});

var bigData = [];
for (var i = 0; i < 1000000; i++) {
  bigData[i] = i;
}


let filterBegin = Date.now()
var filterMappedBigData = bigData.filter(function(value) {
  return value % 2 === 0;
}).map(function(value) {
  return value * 2;
});
let filterEnd = Date.now()
let filtertimeSpent = (filterEnd-filterBegin)/1000 + "secs";


let reducedBegin=Date.now();
var reducedBigData = bigData.reduce(function(acc, value) {
  if (value % 2 === 0) {
    acc.push(value * 2);
  }
  return acc;
}, []);
let reducedEnd = Date.now();
let reducedtimeSpent = (reducedEnd-reducedBegin)/1000 + " secs";

console.log("filtered Big Data:", filtertimeSpent)
console.log("reduced Big Data:", reducedtimeSpent)

// 4. Use the Optional Reduce Arguments
function reducer(accumulator, value, index, array) {
  var intermediaryValue = accumulator + value;

  if (index === array.length - 1) {
    return intermediaryValue / array.length;
  }

  return intermediaryValue;
}

var data = [1, 2, 3, 3, 4, 5, 3, 1];
var mean = data.reduce(reducer, 0);

console.log("Mean:", mean)

// 5. Avoid Common Mistakes when Working with Reduce
var data = ["vote1", "vote2", "vote1", "vote2"];
function reducer(accumulator, value) {
  if (accumulator[value]) {
    accumulator[value] = accumulator[value] + 1;
  } else {
    accumulator[value] = 1;
  }

  return accumulator;
}

var tally = data.reduce(reducer, {});

console.log("Vote1: ", tally.vote1)

// 6. Learn to Flatten and Flatmap Arrays with Reduce
var data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
var flattenedData = data.reduce(function(acc, value) {
  return acc.concat(value);
}, []);

var input = [
  {
    title: "Batman Begins",
    year: 2005,
    cast: [
      "Christian Bale",
      "Michael Caine",
      "Liam Neeson",
      "Katie Holmes",
      "Gary Oldman",
      "Cillian Murphy"
    ]
  },
  {
    title: "The Dark Knight",
    year: 2008,
    cast: [
      "Christian Bale",
      "Heath Ledger",
      "Aaron Eckhart",
      "Michael Caine",
      "Maggie Gyllenhal",
      "Gary Oldman",
      "Morgan Freeman"
    ]
  },
  {
    title: "The Dark Knight Rises",
    year: 2012,
    cast: [
      "Christian Bale",
      "Gary Oldman",
      "Tom Hardy",
      "Joseph Gordon-Levitt",
      "Anne Hathaway",
      "Marion Cotillard",
      "Morgan Freeman",
      "Michael Caine"
    ]
  }
];

var stars = input.reduce(function(acc, value) {
  value.cast.forEach(function(star) {
    if (acc.indexOf(star) === -1) {
      acc.push(star);
    }
  });

  return acc;
}, []);

var data = [1, 2, 3, 4, "5"];
var sum = data.reduceRight(function(acc, value, index) {
  console.log(`Index: ${index}`)
  return acc + value;
}, 0);

console.log("Sum: ", sum)

// 7. Compose Functions with Reduce
function increment(input) { return input + 1;}
function decrement(input) { return input - 1; }
function double(input) { return input * 2; }
function halve(input) { return input / 2; }

var initial_value = 1;

var pipeline = [
  increment,
  increment,
  increment,
  double,
  increment,
  increment,
  halve
];

var final_value = pipeline.reduce(function(acc, fn) {
  return fn(acc);
}, initial_value);

var reversed = pipeline.reduceRight(function(acc, fn) {
  return fn(acc);
}, initial_value)

console.log("final_value: ", final_value)
console.log("reversed: ", reversed)

// 8. Safely inspect nested objects with Reduce
var luke = {
  name: "luke skywalker",
  jedi: true,
  parents: {
    father: {
      jedi: true
    },
    mother: {
      jedi: false
    }
  }
}

var han = {
  name: "han solo",
  jedi: false,
  parents: {
    father: {
      jedi: false
    },
    mother: {
      jedi: false
    }
  }
}

var anakin = {
  name: "anakin skywalker",
  jedi: true,
  parents: {
    mother: {
      jedi: false
    }
  }
}

var characters = [luke, han, anakin];

function fatherWasJedi(character) {
  var path = "parents.father.jedi";
  return path.split(".").reduce(function(obj, field) {
    if (obj) {
      return obj[field];
    }

    return false;
  }, character);
}

characters.forEach(function(character) {
  console.log(character.name + "'s father was a jedi:", fatherWasJedi(character)) 
});