【前端】数组数据操纵：map, filter, sort, reduce

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/u011240016/article/details/84189372

const companies = [
	{ name: "Company One", category: "Finance", start: 1981, end: 2003 }, 
	{ name: "Company Two", category: "Retail", start: 1991, end: 2016 }, 
	{ name: "Company Three", category: "Auto", start: 1983, end: 2007 }, 
	{ name: "Company Four", category: "Retail", start: 1987, end: 2009 }, 
	{ name: "Company Five", category: "Tech", start: 1985, end: 2010 }, 
	{ name: "Company Six", category: "Finance", start: 1988, end: 2000 }, 
	{ name: "Company Seven", category: "Auto", start: 1986, end: 2012 }, 
	{ name: "Company Eight", category: "Retail", start: 1984, end: 2005 }, 
	{ name: "Company Nine", category: "Finance", start: 1998, end: 2013 }, 
];

const ages = [23, 5, 26, 25, 22, 25, 22, 23, 22, 15];

// for(let i = 0; i < companies.length; i++) {
// 	console.log(companies[i])
// }

// forEach
// companies.forEach(function(company) {
// 	console.log(company.name);
// });

// filter
// let canDrink = [];
// for(let i = 0; i < ages.length; i++) {
// 	if(ages[i] >= 21) {
// 		canDrink.push(ages[i]);
// 	}
// }

// const canDrink = ages.filter(function(age) {
// 	if(age >= 21) {
// 		return true;
// 	}
// });

const canDrink = ages.filter(age => age >= 21);

// console.log(canDrink)

// fiter retail companies
// const retailCompanies = companies.filter(function(company) {
// 	if(company.category === "Retail") {
// 		return true;
// 	}
// });

// const retailCompanies = companies.filter( company => (company.category === "Retail" && company.start > 1990));
// console.log(retailCompanies);

// get 80s companies
// const eightiesCompanies = companies.filter(company => (company.start >= 1980 && company.start < 1990));

// map ： 创建新的array
// const companyNames = companies.map(function(company){
// 	return company.name;
// });

// const testMap = companies.map(function(company) {
// 	return `${company.name} [${company.end} - ${company.start}]`;
// });
// const testMap = companies.map(company => `${company.name} [${company.end} - ${company.start}]`);

// console.log(testMap);


// sort
// Sort companies by start year
// const sortedCompanies = companies.sort(function(a, b) {
// 	if(a.start > b.start) {
// 		return 1; // 升序
// 	} else {
// 		return -1;
// 	}
// });

// 等价写法
const sortedCompanies = companies.sort((a, b) => (a.start > b.start ? 1 : -1));
// console.log(sortedCompanies);

// sort ages
// const sortedAges = ages.sort((a,b) => (a > b ? 1 : -1))

// 等价写法
const sortedAges = ages.sort((a,b) => (a - b))

// console.log(sortedAges)

// reduce
// let ageSum = 0;
// for(let i = 0; i < ages.length; i++) {
// 	ageSum += ages[i];
// }

// const ageSum = ages.reduce(function(total, age) {
// 	return total + age;
// }, 0);

// const ageSum = ages.reduce((total, age) => total + age, 0)

// get total years of all companies
const totalYears = companies.reduce(function(total, company){
	return total + (company.end - company.start);
}, 0);
// const totalYears = companies.reduce((total, company) => total + (company.end - company.start), 0);

// console.log(totalYears);


// 综合来看
const combined = ages
	.map(age => age * 2)
	.filter(age => age >= 40)
	.sort((a, b) => a - b)
	.reduce((a, b) => a + b, 0);
console.log(combined);

END.