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JS | Functions & Arrays

Learning Goals

In this exercise you will apply:

  • Array iteration tecniques
  • Using functions to manipulate and transform arrays

Introduction

Manipulating arrays in code is a very common operation. Whether you're creating a total for a shopping cart, grabbing only the first names out of a list of people, or moving a piece on a chessboard, you're probably going to be modifying or manipulating an array in some way.

Let's put this into practice. Use https://repl.it/ to complete the following exercises with your partner.

Requirements

  • Fork this repo
  • Clone this repo into your ~/code/labs
  • Write your code in the js file provided in the starter-code

Submission

Upon completion, run the following commands

$ git add .
$ git commit -m "done"
$ git push origin master

Navigate to your repo and create a Pull Request -from your master branch to the original repository master branch.

In the Pull request name, add your name and last names separated by a dash "-"

Deliverables

A single JavaScript file will be enough for now.

Find the maximum

Define a function maxOfTwoNumbers that takes two numbers as arguments and returns the largest.

Starter Code

function maxOfTwoNumbers(first, second){
  // Your Code Here
}

var largest = maxOfTwoNumbers(2, 6);
console.log(largest);
// 6

Finding Longest Word

Write a function findLongestWord that takes an array of words and returns the length of the longest one.

Starter Code

var words = [
  "mystery",
  "brother",
  "aviator",
  "crocodile",
  "pearl",
  "orchard",
  "crackpot"
];

var longest = findLongestWord(words);
console.log(longest);
// crocodile

Calculating a Sum

Calculating a sum is as simple as iterating over an array and adding each of the elements together.

Semantically reduce is the best method to use for this, but you can use any loop we've discussed so far.

Calculate the sum of the following array:

var numbers = [6, 12, 1, 18, 13, 16, 2, 1, 8, 10];

Starter Code

function sumArray(array){
// Your Code here
}

var total = sumArray(numbers);
// 87

Calculate the Average

Calculating an average is an extremely common task. Let's practice it a bit.

Algorithm

  1. Find the sum as we did in the first exercise
  2. Take the sum from step 1, and divide it by the number of elements in the list.

Level 1: Array of Numbers

Write code to calculate the average of the following array:

var numbers = [2, 6, 9, 10, 7, 4, 1, 9];

Starter Code

function averageNumbers(array){
  // Your code here
}

var average = averageNumbers(numbers);
console.log(average);
// 6

Level 2: Array of Strings

Write code to calculate the average length of the strings inside of the following array:

var words = [
	"seat",
	"correspond",
	"linen",
	"motif",
	"hole",
	"smell",
	"smart",
	"chaos",
	"fuel",
	"palace"
];

Starter Code

function averageWordLength(array){
  // Your code here
}

var averageLength = averageNumbers(words);
console.log(averageLength);
// 5.3

Unique Arrays

Take the following array, remove the duplicates, and return a new array. You're more than likely going to want to check out the indexOf function.

Do this in the form of a function.

Starter Code

function uniquifyArray(array){
  // Your code here
}

var words = [
  "crab",
  "poison",
  "contagious",
  "simple",
  "bring",
  "sharp",
  "playground",
  "poison",
  "communion",
  "simple",
  "bring"
];

var uniqued = uniquifyArray(words);
console.log(uniqued);
// ["crab", "poison", "contagious", "simple", "bring", "sharp", "playground", "communion"]

Finding Elements

Let's create a simple array search.

Write a function that will take in an array of words as one argument, and a word to search for as the other. Return true if it exists, otherwise return false. Don't use indexOf for this one. :)

Starter Code

var words = [
  "machine",
  "subset",
  "trouble",
  "starting",
  "matter",
  "eating",
  "truth",
  "disobedience"
];

var hasMatter = doesWordExist(words, "matter");
console.log(hasMatter);
// true

var hasDog = doesWordExist(words, "dog");
console.log(hasDog);
// false

Counting Repetion

Write a function that will take in an array of words as one argument, and a word to search for as the other. The function will return the number of times that word appears in the array.

Starter Code

var words = [
  "machine",
  "matter",
  "subset",
  "trouble",
  "starting",
  "matter",
  "eating",
  "matter",
  "truth",
  "disobedience"
  "matter"
];

var howManyMatter = howManyTimes(words, "matter");
console.log(howManyMatter);
// 4

var howManyDog = howManyTimes(words, "dog");
console.log(howManyDog);
// 0

Bonus Quest

In the 20×20 grid below; What is the greatest product of four adjacent numbers in the same direction (up, down, left, right)?

var matrix = [
  [08,02,22,97,38,15,00,40,00,75,04,05,07,78,52,12,50,77,91,08],
  [49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,04,56,62,00],
  [81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,03,49,13,36,65],
  [52,70,95,23,04,60,11,42,69,24,68,56,01,32,56,71,37,02,36,91],
  [22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80],
  [24,47,32,60,99,03,45,02,44,75,33,53,78,36,84,20,35,17,12,50],
  [32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70],
  [67,26,20,68,02,62,12,20,95,63,94,39,63,08,40,91,66,49,94,21],
  [24,55,58,05,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72],
  [21,36,23,09,75,00,76,44,20,45,35,14,00,61,33,97,34,31,33,95],
  [78,17,53,28,22,75,31,67,15,94,03,80,04,62,16,14,09,53,56,92],
  [16,39,05,42,96,35,31,47,55,58,88,24,00,17,54,24,36,29,85,57],
  [86,56,00,48,35,71,89,07,05,44,44,37,44,60,21,58,51,54,17,58],
  [19,80,81,68,05,94,47,69,28,73,92,13,86,52,17,77,04,89,55,40],
  [04,52,08,83,97,35,99,16,07,97,57,32,16,26,26,79,33,27,98,66],
  [88,36,68,87,57,62,20,72,03,46,33,67,46,55,12,32,63,93,53,69],
  [04,42,16,73,38,25,39,11,24,94,72,18,08,46,29,32,40,62,76,36],
  [20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,04,36,16],
  [20,73,35,29,78,31,90,01,74,31,49,71,48,86,81,16,23,57,05,54],
  [01,70,54,71,83,51,54,69,16,92,33,48,61,43,52,01,89,19,67,48],
];

var maxProduct = greatestProduct(matrix);
console.log(maxProduct);
// => 57,148,146

Extra Resources