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lodash,js
_.chunk(['a', 'b', 'c', 'd'], 2);
// => [['a', 'b'], ['c', 'd']]
_.chunk(['a', 'b', 'c', 'd'], 3);
// => [['a', 'b', 'c'], ['d']]
// 自己尝试实现个
// 分析思路,参数有2个,用第二个长度来做切割,
function _chunk(arr, num){
let len = arr.length;
if(len<num){
num = len
}
let beishu = Math.ceil(len/num);
let newArr = [];
let temp = 0;
for(let j=0 ; j<beishu ;){
let start = temp;
j++;
let end = j*num;
temp = end;
newArr.push(arr.slice(start,end))
}
return newArr
}
// log(_chunk(['a', 'b', 'c', 'd'], 1))
// 基本算是实现了,但是肯定不是完整,看看源码怎么写的
function chunk(array, size) {
// 转换为数字,防止负数
size = Math.max(size, 0)
// 获取数组的长度
const length = array == null ? 0 : array.length
// 如果数组为空或者切割的长度不够1就返回空数组
if (!length || size < 1) {
return []
}
let index = 0
let resIndex = 0
// 判断切割之后有几个数组,new Array(2)相当于[].length=2
const result = new Array(Math.ceil(length / size))
// 很巧妙的循环判断,边界就是我数组的长度,你从头开始切,切到你需要的尺寸,直到大于数组的长度,就表示不能再切了
// 再一个很巧妙的设计,之前设置了需要切的空数组,每次循环就把当前的数据加入到当前的index里面,循环满了也不用再继续加入了
while (index < length) {
result[resIndex++] = array.slice(index, (index += size))
}
return result
}
总结
- 转换数字且防止负数取最大值
Math.max(size,0)
- 新建空数组
new Array(length)
- 利用空数组配合循环
while(index<length)array[index++]
打造array.push的效果
var array = [1];
var other = _.concat(array, 2, [3], [[4]]);
// console.log(other);
// => [1, 2, 3, [4]]
// console.log(array);
// => [1]
function concat() {
// 判断参数长度
var length = arguments.length;
if (!length) {
return [];
}
var args = Array(length - 1), // 参数
array = arguments[0], // 第一个参数
index = length; // 索引
// 判断长度为0就停止
while (index--) {
// 复制参数导args中
args[index - 1] = arguments[index];
}
// 获取到了所有的参数然后都push到新数组中
return arrayPush(Array.isArray(array) ? copyArray(array) : [array], baseFlatten(args, 1));
}
总结
- 使用while配合index--做循环条件,知道index为0循环停止
- 使用第一种循环配合index-1复制数据
_.compact([0, 1, false, 2, '', 3]);
// => [1, 2, 3]
function __compact(array) {
let resIndex = 0
const result = []
// 过滤参数为null的情况下返回空数组
if (array == null) {
return result
}
// 迭代器遍历数组
for (const value of array) {
// 如果有数据则放到空数组中
if (value) {
// 索引值对应增加
result[resIndex++] = value
}
}
return result
}
// log(__compact([0, 1, false, 2, '', 3]))
总结
1.判断参数是否为null断定有没有传参
2.遍历数组采用for of
3.返回新数组可以采用增加索引值
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