reduce使用总结 javascript

累加

const sum = [1,2,3,4].reduce((accu, cur) => accu + cur, 10); // 20

数组去重

// 常规数组 const uniqueArr = [1,2,3,4,2,3,2,3,5,1].reduce((accu, cur) => !accu.includes(cur) ? accu.concat(cur) : accu, []); // [1,2,3,4,5]// 等价于： [...new Set([1,2,3,4,2,3,2,3,5,1])]; Array.from(new Set(1,2,3,4,2,3,2,3,5,1)); // 对象数组(按属性对object去重) const arr = [ {team: 'The clippers', player:'Paul' }, {team: 'The cavaliers', player:'James' }, {team: 'The nets', player:'Durant' }, {team: 'The lakers', player:'James' } ]; const uniqueArr = arr.reduce((accu, cur) => { if (!accu.find((item) => item.player === cur.player)) { accu.concat(cur); } return accu; }, []); // [ // {team: 'The clippers', player:'Paul'}, // {team: 'The cavaliers', player:'James'}, // {team: 'The nets', player:'Durant'} // ]

递归实现数组降维

const flattenArray = (arr) => { arr.reduce((accu, cur) => Array.isArray(curr) ? accu.concat(func(curr)) : accu.concat(curr), []); }; flattenArray([8, [5, 4], 1, 3, [7, 5, 10, [3, 6, 2]], 4, 3, 2, 4]); // // [ 8, 5, 4, 1, 3, 7, 5, 10, 3, 6, 2, 4, 3, 2, 4 ]

按属性分组

var people = [ {team: 'The clippers', player:'Paul'}, {team: 'The cavaliers', player:'James'}, {team: 'The nets', player:'Durant'}, {team: 'The lakers', player:'James'} ]; function groupBy(objectArray, property) { return objectArray.reduce(function (acc, obj) { var key = obj[property]; if (!acc[key]) { acc[key] = []; } acc[key].push(obj); return acc; }, {}); }var groupedPlayer = groupBy(people, 'player'); // groupedPlayer is: // { //James: [ //{team: 'The lakers', player:'James'}, //{team: 'The cavaliers', player:'James'}, //], //Paul: [{team: 'The clippers', player:'Paul'}], //Durant: [team: 'The nets', player:'Durant'] // }

频率统计

const names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice']; const countedNames = names.reduce(function (allNames, name) { name in allNames ? allNames[name]++ : allNames[name] = 1; return allNames; }, {}); // countedNames is: // { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 }

【reduce使用总结】实现map, filter, forEach等的功能

reduce实现map

Array.prototype.reduceMap = function(callback) { return this.reduce((accu, cur, index) => accu.concat(callback(cur, index)); }, []); }; [1,2,3,4].reduceMap((item, index) => item + index); // [1,3,5,7]

reduce实现forEach

Array.prototype.reduceForEach = function(callback) { this.reduce((accu, cur, index, array) => { callback(cur, index, array); }, []); }; [1, 2, 3, 4].reduceForEach((item, index, array) => { console.log(item, index, array) }); // 1 0 [1,2,3,4] // 2 1 [1,2,3,4] // 3 2 [1,2,3,4] // 4 3 [1,2,3,4]

reduce实现filter

Array.prototype.reduceFilter = function (callback) { return this.reduce((accu, cur, index, array) => callback(cur, index, array)) ? accu.concat(cur) : accu, []); }; [1, 2, 3, 4].reduceFilter(item => item % 2 === 0); // [2, 4]

reduce实现find

const obj = [{ a: 1 }, { a: 2 }, { a: 3 }, { a: 4 }] Array.prototype.reduceFind = function (callback) { return this.reduce((accu, cur, index, array) => { if (callback(cur, index, array)) { if (accu instanceof Array && accu.length === 0) { accu = cur; } } if ((index === array.length - 1) && accu instanceof Array && accu.length === 0) { accu = undefined; } return accu; }, []); }; obj.reduceFind(item => item.a % 2 == 0); // {a: 2} obj.reduceFind(item => item.a % 9 == 0); // undefined