05-arrays.md

Arrays 101

Example arrays with different types of data

const emptyArray = [];
const numberArray = [ 1, 2, 3, 4 ];
const charArray = [ 'a', 'b', 'c', 'd' ];

Display array

const notes = [ 'note1', 'note2', 'note3'];
console.log('Note array', notes);

Get the number of items in the array

const notes = [ 'note1', 'note2', 'note3'];
console.log(`Notes length = ${notes.length}`);

Display the first item in the array

const notes = [ 'note1', 'note2', 'note3'];
console.log(`First Item = ${notes[0]}`);

Dynamically decide what item to display in the array, using an operation to determine item place

const notes = [ 'note1', 'note2', 'note3'];
console.log(`First Item = = ${notes[notes.length - 3]}`);

Undefined items result in an undefined state

const notes = [ 'note1', 'note2', 'note3'];
console.log(`Undefinied Item = ${notes[100]}`);

Resources

• Array

Adding And Removing items from an array

Adding a note to end of array:

const notes = [ 'note1', 'note2', 'note3'];

notes.push('note 4');
console.log('Note array', notes);

Remove last node

const notes = [ 'note1', 'note2', 'note3'];

const poppedNote = notes.pop();
console.log('Note array', notes);
console.log('Popped Note', poppedNote);

Removing first node

const notes = [ 'note1', 'note2', 'note3'];

const shiftedNote = notes.shift();
console.log('Note array after shift', notes);
console.log('Shifted Note', shiftedNote);

Adding an item to the beginning of the array - unshift

const notes = [ 'note1', 'note2', 'note3'];

notes.unshift(shiftedNote);
console.log('Note array after unshift', notes);

Getting an item from an array without changing it

const notes = [ 'note1', 'note2', 'note3'];

const slicedItem = notes.slice(1, 2);
console.log('Note array doesnt change after slice', notes);
console.log('Slaced() Item = ', slicedItem);

Removing an item from a given position in the original array

const notes = [ 'note1', 'note2', 'note3'];

const splicedItem = notes.splice(1, 1);
console.log('Note array is changed after splice()', notes);
console.log('Spliaced() Item = ', splicedItem);

Removing an item from a given position in the original array

const notes = [ 'note1', 'note2', 'note3'];

const splicedItemAdd = notes.splice(1, 1, 'note 2', 'note 3');
console.log('Note array after splice() with an add', notes);

Resources

• Array

Arrays - Foreach()

iterating through a collection with a callback

const notes = [ 'note1', 'note2', 'note3'];
notes.forEach(function(note) {
    console.log(note);
});
console.log();

Iterating through a collection with an arrow function

const notes = [ 'note1', 'note2', 'note3'];
notes.forEach((note) => {
    console.log(note);
});
console.log();

Iterating through a collection with an arrow function

const notes = [ 'note1', 'note2', 'note3'];
notes.forEach((note, index) => {
    console.log(`${note} is in position ${index}`);
});
console.log();

For()

Basic Example

const notes = [ 'note1', 'note2', 'note3'];
for(const positionNumber in notes) {
    console.log(`${notes[positionNumber]} is in position ${positionNumber}`);
}
console.log();

For Loop iterating upwards

const notes = [ 'note1', 'note2', 'note3'];
for(let count = 0; count < notes.length; count++) {
    console.log(`${notes[count]} is in position ${count}`);
}
console.log();

For Loop in reverse order -> iterating backwards

const notes = [ 'note1', 'note2', 'note3'];
for(let count = (notes.length - 1); count >= 0; count--) {
    console.log(`${notes[count]} is in position ${count}`);
}
console.log();

Resources

• Array
• ForEach()

Map() and Reduce()

(todo)

Resources

• Map, filter and reduce
• Map
• Reduce()
• ReduceRight()

Filter()

Filtering items out of an array

const notes = [{
    title: 'note1',
    body: 'body1'},
    {title: 'note2',
    body: 'body2'},
    {title: 'note3',
    body: 'body3'}];

const filteredResult = notes.filter((note) => {
    return note.title.toLowerCase() === query.toLowerCase();
});

console.log(filteredResults(notes, 'note3'));

Searching for an item in an array

const notes = [{
    title: 'note1',
    body: 'body1'},
    {title: 'note2',
    body: 'body2'},
    {title: 'note3',
    body: 'body3'}];

// Searching a valid item - will return the index number the match exists
console.log('Basic search with matching item = ', notes.indexOf('note2'));

// Searching an item - will return -1 for non-matching result
console.log('Basic search with non-matching item = ', notes.indexOf('note5'));

//Compaing Objects
const isEqual = {} === {};
console.log('Are two empty objects equal ', isEqual);

const emptyObjectArray = [{}];
console.log('IndexOf on an empty object will return -1= ', notes.indexOf({}));

// Objects are compared if it's the same obejct in memory, rather than  if two objects contain the same properties
// Compare two different objects then will always return false, as both obejcts will live in different bits within memory

const index = notes.findIndex((note, index) => {
    return note.title === 'note2'
});

console.log('findIndex on a match = ', index);

Resources

• Array
• Filter()