Data Science

Deep Dive

  • What is data science

  • What data science can do

  • Pre-requisites & Skillset

  • Data science workflow

  • R Programming

  • Probability & Statistics

  • Data analysis & Visualization

  • Machine Learning

  • Course Curriculum

  • Q & A

What is data science?

"To gain insights into data through computations, statistics and visualization"

The ability to take data—to be able to understand it, to process it, to extract value from it, to visualize it, to communicate it—that’s going to be a hugely important skill in the next decades - Hal Varian

What data science can do?

  • Predict whether a patient hospitalized due to a heart attach, will have a second heart attach. The prediction is to be based on demographic, diet & clinical measurement for that patient..
  • Predict the price of a stock in 6 months from now, on the basis of company performance measures & economic data.
  • Identify the risk factors for prostate cancer, based on clinical & demographic variables.
  • It can also figure out whether a customer is pregnant or not by capturing their shopping habits from retail stores
  • It also knows your age and gender, what brands you like even if you never told., including your list of interests(which you can edit) to decide what kind of ads  to show you.      
  • It can also predict whether or not your relationship is going to last, based on activities and status updates on social networking sites. Police departments in some major cities also know you're going to commit a crime.    
  • It also tells you what videos you've been watching, what you like to read, & when you're going to quit your job.  
  • It also guess how intelligent you are how satisfied you are with your life, and whether you are emotionally stable or not -simply based on analysis of the 'likes'  you have clicked

this is just the tip of the iceberg

Pre-requisites & skillset

var vs. let / const 

var snack = 'Meow Mix';

function getFood(food) {
    var snack;
    
    if (food) {
        snack = 'Friskies';
        return snack;
    }
    return snack;
}

getFood(false); 
// undefined

var vs. let / const 

let snack = 'Meow Mix';

function getFood(food) {

    if (food) {
        let snack = 'Friskies';
        return snack;
    }
    return snack;
}

getFood(false); 
// A
// B
// 'Meow Mix'
Credit: https://github.com/venegu

var vs. let / const 

let snack = 'Meow Mix';

function getFood(food) {

    if (food) {
        let snack = 'Friskies';
        return snack;
    }
    return snack;
}

getFood(false); 
// A
// B
// 'Meow Mix'
Credit: https://github.com/venegu

IIFE   > Blocks

(function () {  
    var food = 'Meow Mix';
}());  
console.log(food);
// Reference Error

IIFE  > Blocks

{  
    let food = 'Meow Mix';
} 
console.log(food); 
// Reference Error

Scoping

function Person(name) {
    this.name = name;
}

Person.prototype.prefixName = function (arr) {
    return arr.map(function (character) {
        return this.name + character;
    });
};
// Cannot read property 'name' of undefined
// A
// B
function Person(name) {
    this.name = name;
}

Person.prototype.prefixName = function (arr) {
    var that = this;
    return arr.map(function (character) {
        return that.name + character;
    });
};
// Store this

Scoping

function Person(name) {
    this.name = name;
}

Person.prototype.prefixName = function (arr) {
    return arr.map(function (character) {
        return this.name + character;
    }, this);
}

Scoping

function Person(name) {
    this.name = name;
}

Person.prototype.prefixName = function (arr) {
    return arr.map(function (character) {
        return this.name + character;
    }.bind(this));
}

Scoping

Arrow Functions

function Person(name) {
    this.name = name;
}

Person.prototype.prefixName = function (arr) {
    return arr.map((character) => this.name + character );
}

Arrow Functions

const arr = [1, 2, 3, 4, 5];
const squares = arr.map(x => x * x);
const squares = arr.map(function (x) { return x * x });
// Function Expression
// Terse

Strings

String.prototype.includes

var string = 'food';
var substring = 'foo';
console.log(string.indexOf(substring) > -1);
const string = 'food';
const substring = 'foo';
console.log(string.includes(substring)); 
// true
// true

String.prototype.repeat

function repeat(string, count) {
    var strings = [];
    while(strings.length < count) {
        strings.push(string);
    }
    return strings.join('');
}
'meow'.repeat(3); 
// meowmeowmow

Template Literals: Escaping Characters

var text = "This string contains \"double quotes\" which are escaped."
 
let text = `This string contains "double quotes" which are escaped.`

 

Template Literals: Interpolation

const name = 'Tiger';
const age = 13;
console.log(`My cat is named ${name} and is ${age} years old.`);
var name = 'Tiger';
var age = 13;
console.log('My cat is named ' + name + ' and is ' + age + ' years old.');
Credit: https://github.com/venegu

Template Literals: Multi-line Strings

var text = (
  'cat\n' +
  'dog\n' +
  'nickelodeon'
)
var text = [
  'cat',
  'dog',
  'nickelodeon'
].join('\n')
var text = (
  `cat
  dog
  nickelodeon`
)

Template Literals: Expressions

let today = new Date()
let text = `The time and date is ${today.toLocaleString()}`

Template Literals: Multi-line Strings

let book = {
  title: 'Harry Potter and The Sorcercers Stone',
  summary: 'Much magic. Such depth.',
  author: 'J.K. Rowling'
}

let html = `<header>
  <h1>${book.title}</h1>
</header>
<section>
  <div>${book.summary}</div>
  <div>${book.author}</div>
</section>`

Destructuring

Destructuring


var luke = { occupation: 'jedi', father: 'anakin' }
var {occupation, father} = luke;
console.log(occupation); // 'jedi'
console.log(father); // 'anakin'
var [a, b] = [10, 20]
console.log(a); // 10

console.log(b); // 20

Destructuring

function getCoords () {
  return {
    x: 10,
    y: 22
  }
}

var {x, y} = getCoords()
console.log(x); // 10
console.log(y); // 22

Modules

Credit: https://www.flickr.com/photos/lucaohman/3473867313

Exporting in CommonJS

module.exports = 1
module.exports = { foo: 'bar' }
module.exports = ['foo', 'bar']
module.exports = function bar () {}
export default 1
export default { foo: 'bar' }
export default ['foo', 'bar']
export default function bar () {}

Named Exports

module.exports.name = 'David';
module.exports.age = 25;
export var name = 'David';
export var age  = 25;​​

Exporting in ES6

// math/addition.js
function sumTwo(a, b) {
    return a + b;
}

function sumThree(a, b) {
    return a + b + c;
}



export { sumTwo, sumThree };

Exporting in ES6

export function sumTwo(a, b) {
    return a + b;
}

export function sumThree(a, b) {
    return a + b + c;
}

Exporting default bindings

function sumTwo(a, b) {
    return a + b;
}

function sumThree(a, b) {
    return a + b + c;
}


var api = {
    sumTwo  : sumTwo,
    sumThree: sumThree
}
export default api

Importing Modules

var _ = require('underscore');​
import _ from 'underscore';
import { sumTwo, sumThree } from 'math/addition'
import { 
  sumTwo as addTwoNumbers, 
  sumThree as sumThreeNumbers} from
} from 'math/addition'
import * as util from 'math/addition'

Parameters

Default Parameters

function addTwoNumbers(x, y) {
    x = x || 0;
    y = y || 0;
    return x + y;
}
function addTwoNumbers(x=0, y=0) {
    return x + y;
}

addTwoNumbers(2, 4); // 6
addTwoNumbers(2); // 2
addTwoNumbers(); // 0

Rest Parameters

function logArguments() {
    for (var i=0; i < arguments.length; i++) {
        console.log(arguments[i]);
    }
}
function logArguments(...args) {
    for (let arg of args) {
        console.log(arg);
    }
}

Named Parameters

function initializeCanvas(options) {
    var height = options.height || 600;
    var width  = options.width  || 400;
    var lineStroke = options.lineStroke || 'black';
}
function initializeCanvas(
    { height=600, width=400, lineStroke='black'}) {
        ...
    }
function initializeCanvas(
    { height=600, width=400, lineStroke='black'} = {}) {
        ...
    }

Spread Operator

Math.max(...[-1, 100, 9001, -32]) // 9001
var arr = [1, ...[2,3], 4];
console.log(arr); // [1, 2, 3, 4]
var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1.push(...arr2);

Classes

Base Classes

function Person(name, age, gender) {
    this.name   = name;
    this.age    = age;
    this.gender = gender;
}

Person.prototype.incrementAge = function () {
    return this.age += 1;
};

Extended Classes

function Personal(name, age, gender, occupation, hobby) {
    Person.call(this, name, age, gender);
    this.occupation = occupation;
    this.hobby = hobby;
}

Personal.prototype = Object.create(Person.prototype);
Personal.prototype.constructor = Personal;
Personal.prototype.incrementAge = function () {
    return Person.prototype.incrementAge.call(this) += 1;
}

Base Classes in ES6

class Person {
    constructor(name, age, gender) {
        this.name   = name;
        this.age    = age;
        this.gender = gender;
    }
    
    incrementAge() {
      this.age += 1;
    }
}

Extended Classes in ES6

class Personal extends Person {
    constructor(name, age, gender, occupation, hobby) {
      super(name, age, gender);
      this.occupation = occupation;
      this.hobby = hobby;
    }
    
    incrementAge() {
      super.incrementAge();
      this.age += 20;
      console.log(this.age);
    }
}
// Calls parent incrementAge()

Symbols

Unique Property Keys

const key = Symbol();
const keyTwo = Symbol();
const object = {};

>> key === keyTwo 
>> false
object.key = 'Such magic.';
object.keyTwo = 'Much Uniqueness'

Symbols as Concepts

const anakin = 'jedi';
const yoda   = 'jedi master';
const luke   = 'jedi';

const anakin = Symbol();
const yoda   = Symbol();
const luke   = Symbol();

Maps

(Hash) Maps in ES5

var map = new Object();
map[key1] = 'value1';
map[key2] = 'value2';

Seems functional, right...?

Get Own Properties

function getOwnProperty(object, propertyKey) {
    return (object.hasOwnProperty(propertyKey) ? object[propertyKey]: undefined);
}

We should be safe...right?

> getOwnProperty({ hasOwnProperty: 'Hah, overwritten'}, 'Pwned');
> TypeError: Propery 'hasOwnProperty' is not a function

Credit: http://memesvault.com/nooo-meme-darth-vader/

Second time is the charm.

function getOwnProperty(object, propertyKey) {
    return (Object.prototype.hasOwnProperty(object, propertyKey) ? object[propertyKey]: undefined);
}

credit: http://deloiz.blogspot.com/2014/01/Pusheen.html

Maps in ES6

let map = new Map();
> map.set('name', 'david');
> map.get('name'); // david
> map.has('name'); // true
// key
// value

Keys can be more than strings!

Arbitrary values as keys

let map = new Map([
    ['name', 'david'],
    [true, 'false'],
    [1, 'one'],
    [{}, 'object'],
    [function () {}, 'function']
]);

for (let key of map.keys()) {
    console.log(typeof key);
    // > string, boolean, number, object, function
};

.entries( )

for (let entry of map.entries()) {
  console.log(entry[0], entry[1]);
}
for (let [key, value] of map.entries()) {
  console.log(key, value);
}

WeakMaps

Classes 101

class Person {
    constructor(age) {
        this.age = age;
    }
    
    incrementAge() {
      this.age += 1;
    }
}

Private data?

Naming Conventions

class Person {
    constructor(age) {
        this._age = age;
    }
    
    _incrementAge() {
      this._age += 1;
    }
}

WeakMaps to the rescue!

(Maybe they're not so weak)

WeakMaps for Privacy

let _age = new WeakMap();
class Person { 
  constructor(age) {
    _age.set(this, age);
  }

  incrementAge() {
    let age = _age.get(this);
      if(age > 90) {
        console.log('Midlife crisis');
      }
  }
}
> const person = new Person(90);
> person.incrementAge(); // 'Midlife crisis'
> Reflect.ownKeys(person); // []

 

credit: http://wildermuth.com/images/pinky-promise_2.jpg

Promises

Callback Hell

func1(function (value1) {
  func2(value1, function(value2) {
    func3(value2, function(value3) {
      func4(value3, function(value4) {
        func5(value4, function(value5) {
          // Do something with value 5
        });
      });
    });
  });
});

D

O

O

M

Promises

func1(value1)
  .then(func2(value1) { })
  .then(func3(value2) { })
  .then(func4(value3) { })
  .then(func5(value4) { 
    // Do something with value 5 
  });

Promises

Promises

new Promise(resolve => resolve(data))
    .then(result => console.log(data));




new Promise((resolve, reject) => 
    reject(new Error('Failed to fufill Promise')))
    .catch(reason => console.log(reason));

Promises

Promises

var fetchJSON = function(url) {  
  return new Promise((resolve, reject) => {
    $.getJSON(url)
      .done((json) => resolve(json))
      .fail((xhr, status, err) => reject(status + err.message));
  });
}

Parallelizing using Promises

var urls = [ 
  'http://www.api.com/items/1234',
  'http://www.api.com/items/4567'
];

var urlPromises = urls.map(fetchJSON);

Promise.all(urlPromises)  
  .then(function(results) {
     results.forEach(function(data) {
     });
  })
  .catch(function(err) {
    console.log("Failed: ", err);
  });

Generators

Syntax

function* sillyGenerator() {
    yield 1;
    yield 2;
    yield 3;
    yield 4;
}
var generator = sillyGenerator();
var value = generator.next();
> console.log(value); // { value: 1, done: false }
> console.log(value); // { value: 2, done: false }
> console.log(value); // { value: 3, done: false }
> console.log(value); // { value: 4, done: false }

What about using return?

Return in a Generator

function* sillyGenerator() {
    yield 1;
    yield 2;
    yield 3;
    yield 4;
    return 5;
}

for(let val of sillyGenerator()) {
    console.log(val); // 1, 2, 3, 4
}

Real Generator Function

function* factorial(){
  let [current, total] = [0, 1];

  while (true){
    yield total;
    current++;
    total = total * current;
  }
}

for (let n of factorial()) {
  console.log(n); 
  if(n >= 100000) {
    break;
  }
}

Writing Sync-Async 

function request(url) {
    getJSON(url, function(response) {
        generator.next(response);
    });
}

function* getData() {
    var entry1 = yield request('http://some_api/item1');
    var data1  = JSON.parse(entry1);
    var entry2 = yield request('http://some_api/item2');
    var data2  = JSON.parse(entry2);
}

Not without problems though...

 

  • How do we handle errors?

  • getJSON not in control

  • Parallelize?

Generators & Promises

function request(url) {
    return new Promise((resolve, reject) => {
        getJSON(url, resolve);
    });
}

Generators & Promises

function iterateGenerator(gen) {
    var generator = gen();
    var ret;
    (function iterate(val) {
        ret = generator.next();
        if(!ret.done) {
            ret.value.then(iterate);
        } else {
            setTimeout(function() {
                iterate(ret.value);
            });
        }
    })(); 
}

Generators & Promises

iterateGenerator(function* getData() {
  var entry1 = yield request('http://some_api/item1');
  var data1  = JSON.parse(entry1);
  var entry2 = yield request('http://some_api/item2');
  var data2  = JSON.parse(entry2);
});

Alternate Solution?

Beyond ES6

Async / Await (ES7)

var request = require('request');
 
function getJSON(url) {

  request(url, function(error, response, body) {
    return body;
  });
}
 
function main() {
  var data = getJSON('http://some_api/item1');
  console.log(data); // Undefined
}
 
main();

Async / Await (ES7)

var request = require('request');
 
function getJSON(url) {
  return new Promise(function(resolve, reject) {
    request(url, function(error, response, body) {
      resolve(body);
    });
  });
}
 
async function main() {
  var data = await getJSON();
  console.log(data); // NOT undefined!
}
 
main();
console.log('The data is: ');

Thank you everyone!

Github: https://github.com/DrkSephy
Blog: http://drksephy.github.io/blog/
LinkedIn: https://www.linkedin.com/in/drksephy
Twitter: https://twitter.com/DrkSephy
ES6 Cheatsheet: https://github.com/DrkSephy/es6-cheatsheet

Copy of ECMAScript 2015

By Data Science Portal

Source: kefka

Copy of ECMAScript 2015

An overview of ES6 features.

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