155. Advanced Arrays

//Advanced Arrays

const array = [1, 2, 10, 16];

const newArray = array.forEach((num) => {
	num * 2;
} )

console.log(newArray);

we should use push to make it new.

//Advanced Arrays

const array = [1, 2, 10, 16];

const double = []
const newArray = array.forEach((num) => {
	double.push(num * 2);
} )

console.log(double);

map, filter, reduce

forEach vs map

Map have a return element.

//Advanced Arrays

const array = [1, 2, 10, 16];

const double = []
const newArray = array.forEach((num) => {
	double.push(num * 2);
} )

console.log('forEach',double);

// map, filter, reduce

const mapArray = array.map((num)=> {
	return num * 2;
});

console.log('map', mapArray);

^'map' is shorter and simpler than 'forEach'.

reference.

If you have a single parameter with an arrow function, you can actually avoid the brackets.

const mapArray = array.map((num)=> {
	return num * 2;
});

const mapArray = array.map(num=> {
	return num * 2;
});

And again because we're returning a single line here we can do like this.

const mapArray = array.map(num=> num * 2);

.

//Advanced Arrays

const array = [1, 2, 10, 16];

const double = []
const newArray = array.forEach(num => {
	double.push(num * 2);
} )

console.log('forEach',double);

// map, filter, reduce

const mapArray = array.map(num=> num * 2);

console.log('map', mapArray);  

filter

//Advanced Arrays

const array = [1, 2, 10, 16];

const double = []
const newArray = array.forEach(num => {
	double.push(num * 2);
} )

console.log('forEach',double);

// map, filter, reduce

const mapArray = array.map(num=> num * 2);

console.log('map', mapArray);  

//filter 
const filterArray =array.filter( num => {
	return num > 5 
})

console.log('filter', filterArray);

//Advanced Arrays

const array = [1, 2, 10, 16];

const double = []
const newArray = array.forEach(num => {
	double.push(num * 2);
} )

console.log('forEach',double);

// map, filter, reduce

const mapArray = array.map(num=> num * 2);

console.log('map', mapArray);  

//filter 
const filterArray =array.filter( num => num === 5);

console.log('filter', filterArray);

reduce

acc is accumulator

//reduce
const reduceArray = array.reduce((accumulator, num)=>{
	return accumulator + num; 
},0)

Here accumulator's default value is 0.

//Advanced Arrays

const array = [1, 2, 10, 16];

const double = []
const newArray = array.forEach(num => {
	double.push(num * 2);
} )

console.log('forEach',double);

// map, filter, reduce

const mapArray = array.map(num=> num * 2);

console.log('map', mapArray);  

//filter 
const filterArray =array.filter( num => {
	return num > 5 
})

console.log('filter', filterArray);

//reduce
const reduceArray = array.reduce((accumulator, num)=>{
	return accumulator + num; 
},0)

console.log('reduce', reduceArray);

^we get 29 ( 1+2+10+16 = 29 )

If you change the default value of accumulator to 5,

//reduce
const reduceArray = array.reduce((accumulator, num)=>{
	return accumulator + num; 
},5)