30s Array -- 创建数组篇(一) · 前端知识 -- 学习整理

>[success] # 30s Array -- 创建数组篇(一) ~~~ 1.本章节代码通过整理30s 项目中数组篇章知识点，对涉及创建新数组的代码片段整理 ~~~ >[info] ## 一直一个范围生成的数组每一项间隔和开始项值相等 ~~~ 1.从给定的正整数开始，直至指定的限制一个限制整数生成数组，举个例子给定项5，限制项25 生成的结果[5,10,15,20,25] ~~~ >[danger] ##### 代码实现 [先了解Array.from](https://www.kancloud.cn/cyyspring/more/1328936) [原文来源](https://www.30secondsofcode.org/js/s/arithmetic-progression) ~~~ const arithmeticProgression = (n,lim)=>Array.from({length:Math.ceil(lim/n)},(v,i)=>(i+1)*n) console.log(arithmeticProgression(5,25)) // [ 5, 10, 15, 20, 25 ] ~~~ >[info] ## 通过回调函数动态作为参数生成数组 ~~~ 1.使用给定的函数生成具有给定数量的项的数组 ~~~ [原文链接](https://www.30secondsofcode.org/js/s/generate-items) >[danger] ##### 30s ~~~ const {log} =console const generateItems = (n,fn)=>Array.from({length:n},(_,i)=>fn(i)) log(generateItems(10, Math.random)) ~~~ >[info] ## 生成二维数组 ~~~ 1.生成二维数组 ~~~ [原文链接](https://www.30secondsofcode.org/js/s/initialize2-d-array) >[danger] ##### 30s ~~~ const {log} =console const initialize2DArray = (w, h, val = null) => Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val)); log(initialize2DArray(3, 2)) // [ [ null, null, null ], [ null, null, null ] ] ~~~ >[info] ## 根据给出数组首尾项和每项间隔生成一个等差数组 ~~~ 1.初始化一个范围数组，例如想生成一个0-9 每个值间隔为2的数组[0, 2, 4, 6, 8] ~~~ [原文链接](https://www.30secondsofcode.org/js/s/initialize-array-with-range) >[danger] ##### 30s ~~~ const {log} =console const initializeArrayWithRange = (end, start = 0, step = 1) => Array.from( { length: Math.ceil((end - start + 1) / step) }, (_, i) => i * step + start ); initializeArrayWithRange(5); // [0, 1, 2, 3, 4, 5] initializeArrayWithRange(7, 3); // [3, 4, 5, 6, 7] initializeArrayWithRange(9, 0, 2); // [0, 2, 4, 6, 8] ~~~ >[info] ## 用指定的值初始化并填充一个数组 ~~~ 1.用指定的值初始化并填充一个数组 ~~~ [原文链接](https://www.30secondsofcode.org/js/s/initialize-array-with-values) >[danger] ##### 30s ~~~ const {log} =console const initializeArrayWithValues = (n, val = 0) => Array.from({ length: n }).fill(val); log(initializeArrayWithValues(5, 3)) // [ 3, 3, 3, 3, 3 ] ~~~ >[info] ## 根据给出数组首尾项和每项间隔生成一个等差数组倒序 ~~~ 1.初始化一个范围数组，例如想生成一个0-9 每个值间隔为2的数组[8, 6, 4, 2, 0] ~~~ [原链接](https://www.30secondsofcode.org/js/s/initialize-array-with-range-right) >[danger] ##### 30s ~~~ const {log} =console const initializeArrayWithRangeRight = (end, start = 0, step = 1) => Array.from({ length: Math.ceil((end + 1 - start) / step) }).map( (v, i, arr) => (arr.length - i - 1) * step + start ); log(initializeArrayWithRangeRight(7, 3)) // [ 7, 6, 5, 4, 3 ] ~~~ >[info] ## 创建一个N维数组并且填充 ~~~ 1.现在有个需求已知一个给定值，想用这个值填充自动生成的多维数组，举个例子，已知填充数字为'1' 一共需要两层，每层三项，因此生成的数组为'[ [ 1, 1, 1 ], [ 1, 1, 1 ], [ 1, 1, 1 ] ]' ~~~ [原链接]([https://www.30secondsofcode.org/js/s/initialize-nd-array](https://www.30secondsofcode.org/js/s/initialize-nd-array)) >[danger] ##### 30s ~~~ 1.这种嵌套的逻辑，首先明确一点事递归，然后需要已知的参数，最终项的内容，以及每一层需要有多少项 2.生成指定长度的数组，这里优先考虑'Array.from'api，每一项的内容参考'map' api ~~~ ~~~ const initializeNDArray = (val, ...args) => args.length === 0 ? val : Array.from({ length: args[0] }).map(() => initializeNDArray(val, ...args.slice(1)) ); log(initializeNDArray(1,3,3)) // [ [ 1, 1, 1 ], [ 1, 1, 1 ], [ 1, 1, 1 ] ] ~~~ >[info] ## 迭代器函数和初始种子值构建数组 ~~~ 1.下面代码是开阔思路，可以通过Array.from 实现类似效果 ~~~ [unfold](https://www.30secondsofcode.org/js/s/unfold) ~~~ const unfold = (fn, seed) => { let result = [], val = [null, seed]; while ((val = fn(val[1]))) result.push(val[0]); return result; }; ~~~ 个需求相加 ~~~