Hack Reactor Underscore Exercise Answers

underscoreEx.js

'use strict';
var _ = require('underscore');

//######### EXAMPLE 1 #################/
//use _.reduce to multiply all the values in an array

var arr = [10,20,40,50,60,70];
var multiplied = _.reduce(arr, function (x, y) { return x * y; });

//tests
console.log(multiplied); //1680000000

//######### EXAMPLE 2 #################/
//Use _.reduce to concatenate all strings in an array.

var str = ['cool', 'wicked', 'slick', 'dope'];
var output1 = _.reduce(str, function(word1, word2) { return word1.concat(word2); });
var output2 = _.reduce(str, function(word1, word2) { return word1 + ' ' + word2; });

//tests
console.log(output1); //coolwickedslickdope
console.log(output2); //cool wicked slick dope


//######### EXAMPLE 3 #################/
//Write a function that takes an array of names and congratulates them.

var input = ['Steve', 'Sally', 'George', 'Gina'];
var newString =  'Congratulations ' +  _.reduce(input, function(x, y) { return  x + ', ' + y; }) + '!';
//tests
console.log(newString); //Congratulations Steve, Sally, George, Gina!

//######### EXAMPLE 3i #################/
//BASIC _.PLUCK WORKS LIKE THIS
var objArray = [{ name : 'Biff Tannin', email: '[email protected]'}, {name: 'Hans Gruber', email: '[email protected]' }, 
           { name : 'Napolean Dynamite', email: '[email protected]'}, { name: 'Boo Radley', email: '[email protected]' } ];
//_.pluck takes an object and a property name and returns the property name's value. 

var getNames = _.pluck(objArray, 'name'); //pluck the values belonging to the key/property 'name'
var getEmails = _.pluck(objArray, 'email'); //pluck the values belonging to the key/property 'email'
console.log(getNames.join(', ')); //Biff Tannin, Hans Gruber, Napolean Dynamite, Boo Radley
console.log(getEmails.join(', ')); //bifftanin@gmail.com, [email protected], [email protected], [email protected]

//Write your own version of pluck called myPluck.

var myPluck = function(objArr, property){
  var newArr = [];  //initialize blank array that we will push to
  objArr.forEach(function(object){
    for (var prop in object)
      if (prop === property) { newArr.push(object[prop]); }
  });
  return newArr;
};

//or using a good ol' classic for loop

var stooges = [{name: 'moe', age: 40}, {name: 'larry', age: 50}, {name: 'curly', age: 60}];

var myPluck = function(obj, propName) {
    var arr = [];
    for (var i = 0; i < obj.length; i++) {
        for (var prop in obj[i]) {
            if (prop === propName)
                arr.push(obj[i][prop]);
        }
    }
    return arr;
}

//tests
console.log(myPluck(stooges, 'name')); //[ 'moe', 'larry', 'curly' ]
console.log(myPluck(stooges, 'age')); // [ 40, 50, 60 ]

console.log(myPluck(objArray, 'name')); //[ 'Biff Tannin','Hans Gruber','Napolean Dynamite', 'Boo Radley' ]
console.log(myPluck(objArray, 'email')); // [ '[email protected]','[email protected]','[email protected]','[email protected]' ]

  
//############EXAMPLE 3ii###################/

var addThem = _.partial(function(a,b,c){ return a + b + c; }, 5, 6);
//power function that allows you to determine the exponential
var powerAny = _.partial(Math.pow, 2); //2^3;
//power function with a set exponential ie. everything squared, everything cubed
var powerTwo = _.partial(Math.pow, _, 2); //everything will be squared
var powerThree = _.partial(Math.pow, _, 3); //everything will be cubed

//tests
console.log(addThem(4)); //15 (adds 4 + 5 + 6 = 15)
//Evaluates Math.power(2,3)
console.log(powerAny(3)); //8
//Evaluates Math.power(3,2)
console.log(powerTwo(3)); //9
//Evaluates Math.power(3,3)
console.log(powerThree(3)); // 27

//########### EXAMPLE 3iii ###############/
// Use _.filter to return all strings in an array that start with the letter 'Z'

var str = ['Zed', 'zeek', 'Zoro', 'god', 'jumanji'];

var zeeWord = _.filter(str, function(val) { return  val.charAt(0) === 'Z'; } );
//use regExp and match instead
var zeeWord2 = _.filter(str, function(val) { return  val.match(/^Z/); } );

//tests
console.log(zeeWord); //[ 'Zed', 'Zoro' ]
console.log(zeeWord2); //[ 'Zed', 'Zoro' ]

//########### EXAMPLE 3iv ###############/
//Use _.where to return all animals who contain the value 3 at the property name space.

var input = [ { name: 'Tiger', space: 7}, { name: 'Tiger2', space: 1}, { name: 'Tiger3', space: 3}, { name: 'Tiger4', space: 3} ];
// return array of objects where property space is set to 3
var output = _.where(input, { space: 3 });

//tests
console.log(output);
//[ { name: 'Tiger3', space: 3 }, { name: 'Tiger4', space: 3 } ]