array sorting (js) | Chinese Rule of Eight

var fruits = ["Banana", "Orange", "Apple", "Mango"];

fruits.sort();

console.log(fruits);

fruits.reverse();

console.log(fruits);

by default, when we use sort, it compares by string, which is what we don’t want.

Custom Sorting

Thus, we use custom sorting

var points = [40, 100, 1, 5, 25, 10];

points.sort(); // wrong

console.log(points); // [ 5, 40, 25, 100, 10, 1 ]

// the compare function should

// return a negative, zero, or positive value

do it like so…

var random = [2,5,46,7,4,6,45,2,55,6,47,56,75,67,4,63,45,345];

random.sort(function(a,b){

if (a<b) return -1; // return a, b

if (a>b) return 1; // return b, a

else return 0;

});

you can also see the ordering of integers by subtracting them. positive means left number is larger. negative means left number is smaller.

// When comparing 40 and 100, the sort() method calls

// the compare function(40,100).

// The function calculates 40-100, and returns -60 (a negative value).

// The sort function will sort 40 as a value lower than 100.

points.sort(function(a, b) {

// return b-a

// b (100) - a (40) = 60. sort a (40) larger than b (100) --> 100 40

// return a - b

// a (40) - b(100) = -60 sort a (40) smaller than b (100) --> 40 100

// if a + b

return a+b;

});

console.log(points);

console.log(Math.max.apply(null, points));

console.log(Math.min.apply(null, points));

get maximum

function getMax(arr) {

let index = 0;

let length = arr.length;

let max = -Infinity;

while (index < length) {

if (arr[index] > max) {

max = arr[index];

}

index++;

}

return `max of ${arr} is ${max}`;

}

console.log(getMax(points));

get 2nd max

function getSecondMax(arr) {

console.log(`get max for array: ${arr}`);

let len = arr.length; console.log(`length of array is: ${len}`)

var max = -Infinity;

var secondMax = -Infinity;

let i = 0;

while (i < len) {

if (arr[i] > max) { // we found larger.

// so we get secondMax to take on the previous max

secondMax = max;

// assign new max

max = arr[i];

}

i++;

}

// max

return `second max of ${arr} is ${secondMax}`;

}

console.log(getSecondMax(points));

get minimum

function getMin(arr) {

let length = arr.length;

let index = 0;

let min = +Infinity;

while (index < length) {

if (arr[index] < min) {

min = arr[index];

}

index++;

}

return `Minimum of ${arr} is ${min}`;

}

console.log(getMin(points));

Sorting Objects

var cars = [

{type:"Mercedes", year:2001},

{type:"Volvo", year:2016},

{type:"Audi", year:2001},

{type:"Saab", year:2001},

{type:"BMW", year:2010}];

cars.sort(function(a, b){

let x = a.type;

let y = b.type;

console.log(`${x}, ${y} -----> is greater? ${x>y}`);

//if (x < y) {return 1;} // x sorted AFTER y

//if (x > y) {return -1;} // x sorted BEFORE y

if (x < y) {return -1;} // go negative...x goes before y

if (x > y) {return 1;} // go positive...x goes after y

return 0; // do nothing

});

console.log(cars);