Reduce

reduce1.js

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);

console.log(result);
// Object {angular: 3, react: 4, ember: 1, vanilla: 1}

reduce2.js

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;
}

// console.time('bigData');
var filterMappedBigData = bigData.filter(function(value) {
  return value % 2 === 0;
}).map(function(value) {
  return value * 2;
});
// console.timeEnd('bigData');

// console.time('bigDataReduce');
var reducedBigData = bigData.reduce(function(acc, value) {
  if (value % 2 === 0) {
    acc.push(value * 2);
  }
  return acc;
}, []);
// console.timeEnd('bigDataReduce');

reduce3.js

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);

reduce4.js

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);
  return acc + value;
}, 0);

console.log(sum);

reduce5.js

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, reversed);

reduce6.js

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));
});