## An Introduction to Vectors

In the following video tutorial I discuss about Vectors. Understanding Vectors is helpful towards understanding Machine Learning.

This is the primary reason that I decided to create Lectures on Mathematics for Machine Learning.

## Introduction to HTML

If you are wondering how to build websites or web applications then this Lecture will be helpful for you.

In this Lecture I will discuss

1. Technologies needed to build Websites or Web Applications
2. Introduction to HTML

Code is available on Github

Technologies needed to build Websites or Web Applications
The basic technologies required to create a website are HTML, CSS and Javascript.
We will explore HTML in this Lecture. CSS and Javascript are topics for coming lectures.

What is HTML?
Hyper Text Markup Language can be used to structure a web page. It is a Markup Language.

HTML Elements
You can use the following elements to build your Page.

• Paragraph
• Images
• Lists

## Learn about Conditional Statements in Javascript

In this Lecture we will discuss about conditional statements in javascript

• if – else statement
• switch statement
• ternary operator

The code examples below are also available on Github

if…else

Syntax

if (condition) {
// code
} else {
// code
}

else if
To add more else conditions you can use else if clause

if (1<x<2) {

} else if (2<x<3) {

} else {

}

We can use conditional operators like <, >, <= etc.

if(x == ‘A’) {

}

From the documentation

Any value that is not false, undefined, null, 0, NaN, or an empty string (”) actually returns true when tested as a conditional statement, therefore you can simply use a variable name on its own to test whether it is true, or even that it exists (that is, it is not undefined.)

if (data) {
console.log(data);
}

Switch Case
If-else is good when we have few conditions to take care of. What if we want to add more conditions. Let us look at an example

let day = ‘Monday’
switch(day) {
case ‘Monday’:
console.log(‘Today is Monday’)
break;
case ‘Tuesday’:
console.log(‘Today is Tuesday’)
break;
case ‘Wednesday’:
console.log(‘Today is Wednesday’)
break;
default:
console.log(‘No Match’)
}

This example demonstrates how to use switch statements.

Ternary Operator
It’s a convenient way to write if-else in a compact manner.

let x = 8

if(x>2) {
// print 3
} else {
// print 5
}

we can write

let x = 8
(x > 2) ? 3 : 5

## Learn about some useful methods in Javascript Arrays

In this tutorial we will explore some methods which will help you to do certain operations on Javascript Arrays.

The code for this lecture is available on Github

Consider this string

`let fruits = 'Mango, Peach, Banana';`

What if we want to separate out the fruits from this String i.e. get an array of fruits.

To do this we can use the split() method.

split()
In order to use split() we need to pass the character which needs to be used to perform the split.

```let fruitArray = fruits.split(',');
fruitArray // ['Mango', 'Peach', 'Banana']
fruitArray[0] // Mango```

To combine all the array elements back, so that we can get a String, we can use the join() method.

join()

`fruitArray.join('-') // 'Mango-Peach-Banana'`

Alternatively we can use the toString() method.

How to add and remove elements to or from an Array?

To add or remove an element at the end of the Array you can use push() and pop()

push()
push() lets us add an element to the end of the Array.

`fruitArray.push('Orange')`

pop()
pop() lets us remove an element from the end of the Array.

`fruitArray.pop()`

Similarly, to add or remove an element at the start of the Array you can use unshift() and shift()

## Arrays in Javascript – The Basics

What are Arrays ?

Arrays can be used to store a list of data items. Like a list of numbers or objects.

`let ageList = [15, 17, 25, 16, 14]`

So if we do not use arrays then we need to declare separate variables for all the ages. Imagine if we had 100 people. Declaring 100 variables will be very inefficient.

Each element in an array is stored at an index. Indexes start from 0.

`Index : 0 1 2 3 4 Value : 15 17 25 16 14`

How to access elements in an array ?

It is easy to access the elements stored in the array using index.

Like if we want to get element stored at the 3rd location we can use

`ageList[3]`

Similarly we can assign new value to an index

`ageList[3] = 32`

How to find number of items in the array ?

To find the length of array or number of items in the array we can use the length property.

`ageList.length`