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数组分组: 

含义: 数据按照某个特性归类   

1. reduce+fn(cur, index)作为对象的key,值为按照fn筛选出来的数据

// 利用reduce分组
function group(arr, fn) {// 不是数组if (!Array.isArray(arr)) {return arr}// 不是函数if (typeof fn !== 'function') {throw new TypeError('fn必须是一个函数')}var vreturn arr.reduce((obj, cur, index) => {v = fn(cur, index)if (!Reflect.hasOwnProperty.call(obj, v)) {obj[v] = []}obj[v].push(cur)return obj}, {})
}// 按照字符串长度分组
let products = ["apple", "pear", "orange", "peach"];
const f1 = v => v.length
console.log(group(products, f1), 
);// 按照分数分组
result = [{name: "tom",score: 60
}, {name: "Jim",score: 40
}, {name: "Nick",score: 88
}]
const fn = v => v.score >= 60console.log(group(result, fn), 
);

2.filter+fn(value, index)作为对象的key,值为按照fn筛选出来的数据

// 利用forEach和filter分组
function group(arr, fn) {// 不是数组if (!Array.isArray(arr)) {return arr}// 不是函数if (typeof fn !== 'function') {throw new TypeError('fn必须是一个函数')}let obj = {}arr.forEach((item, key) => {const v = fn(item, key)obj[v] = arr.filter((ee, ix) => fn(ee, ix) === v)});return obj
}// 按照字符串长度分组
let products = ["apple", "pear", "orange", "peach"];
const f1 = v => v.length
console.log(group(products, f1), 
);// 按照分数分组
result = [{name: "tom",score: 60
}, {name: "Jim",score: 40
}, {name: "Nick",score: 88
}]
const fn = v => v.score >= 60console.log(group(result, fn), 
);