---
id: 595011cba5a81735713873bd
title: 每组排名最高
challengeType: 5
videoUrl: ''
dashedName: top-rank-per-group
---
# --description--
任务:
在每个组中查找排名前N位的数据,其中N作为参数提供。等级和组的名称也作为参数提供。
鉴于以下数据:
```
[
{姓名:'Tyler Bennett',id:'E10297',薪水:32000,部门:'D101'},
{姓名:'John Rappl',id:'E21437',薪水:47000,部门:'D050'},
{姓名:'George Woltman',id:'E00127',薪水:53500,部门:'D101'},
{name:'Adam Smith',id:'E63535',薪水:18000,部门:'D202'},
{姓名:'Claire Buckman',id:'E39876',薪水:27800,部门:'D202'},
{姓名:'David McClellan',id:'E04242',薪水:41500,部门:'D101'},
{name:'Rich Holcomb',id:'E01234',薪水:49500,dept:'D202'},
{姓名:'Nathan Adams',id:'E41298',薪水:21900,部门:'D050'},
{姓名:'Richard Potter',id:'E43128',薪水:15900,部门:'D101'},
{姓名:'David Motsinger',id:'E27002',薪水:19250,dept:'D202'},
{姓名:'Tim Sampair',id:'E03033',薪水:27000,部门:'D101'},
{姓名:'Kim Arlich',id:'E10001',薪水:57000,部门:'D190'},
{name:'Timothy Grove',id:'E16398',薪水:29900,部门:'D190'}
]。
```
通过调用topRankPerGroup(10, data, 'dept', 'salary')
可以对每个部门的前10名员工进行排名。给出以下数据:
[ {name:'Friday 13th',类型:'恐怖',评分:9.9}, {姓名:“榆树街上的梦魇”,类型:'恐怖',等级:5.7}, {name:'Titanic',类型:'drama',评分:7.3}, {name:'Maze Runner',类型:'scifi',评级:7.1}, {name:'Blade runner',类型:'scifi',评分:8.9} ]。通过调用
topRankPerGroup(1, data, 'genre', 'rating')
可以在每个类型中对排名最高的电影进行排名
# --hints--
`topRankPerGroup`是一个函数。
```js
assert(typeof topRankPerGroup === 'function');
```
`topRankPerGroup`在负n值上返回undefined。
```js
assert(typeof topRankPerGroup(-1, []) === 'undefined');
```
第一部门必须是D050
```js
assert.equal(res1[0][0].dept, 'D050');
```
第一部门必须是D050
```js
assert.equal(res1[0][1].salary, 21900);
```
最后一个部门必须是D202
```js
assert.equal(res1[3][3].dept, 'D202');
```
`topRankPerGroup(1, ...)`必须仅返回每组的排名最高的结果。
```js
assert.equal(res2[2].length, 1);
```
`topRankPerGroup(1, ...)`必须仅返回每组的排名最高的结果。
```js
assert.equal(res3[2][1].name, 'Maze Runner');
```
# --seed--
## --after-user-code--
```js
const testData1 = [
{ name: 'Tyler Bennett', id: 'E10297', salary: 32000, dept: 'D101' },
{ name: 'John Rappl', id: 'E21437', salary: 47000, dept: 'D050' },
{ name: 'George Woltman', id: 'E00127', salary: 53500, dept: 'D101' },
{ name: 'Adam Smith', id: 'E63535', salary: 18000, dept: 'D202' },
{ name: 'Claire Buckman', id: 'E39876', salary: 27800, dept: 'D202' },
{ name: 'David McClellan', id: 'E04242', salary: 41500, dept: 'D101' },
{ name: 'Rich Holcomb', id: 'E01234', salary: 49500, dept: 'D202' },
{ name: 'Nathan Adams', id: 'E41298', salary: 21900, dept: 'D050' },
{ name: 'Richard Potter', id: 'E43128', salary: 15900, dept: 'D101' },
{ name: 'David Motsinger', id: 'E27002', salary: 19250, dept: 'D202' },
{ name: 'Tim Sampair', id: 'E03033', salary: 27000, dept: 'D101' },
{ name: 'Kim Arlich', id: 'E10001', salary: 57000, dept: 'D190' },
{ name: 'Timothy Grove', id: 'E16398', salary: 29900, dept: 'D190' }
];
const res1 = topRankPerGroup(10, testData1, 'dept', 'salary');
const testData2 = [
{ name: 'Friday 13th', genre: 'horror', rating: 9.9 },
{ name: "Nightmare on Elm's Street", genre: 'horror', rating: 5.7 },
{ name: 'Titanic', genre: 'drama', rating: 7.3 },
{ name: 'Maze Runner', genre: 'scifi', rating: 7.1 },
{ name: 'Blade runner', genre: 'scifi', rating: 8.9 }
];
const res2 = topRankPerGroup(1, testData2, 'genre', 'rating');
const res3 = topRankPerGroup(2, testData2, 'genre', 'rating');
```
## --seed-contents--
```js
function topRankPerGroup(n, data, groupName, rankName) {
return true;
}
```
# --solutions--
```js
const collectDept = function (arrOfObj, groupName) {
const collect = arrOfObj.reduce((rtnObj, obj) => {
if (rtnObj[obj[groupName]] === undefined) {
rtnObj[obj[groupName]] = [];
}
rtnObj[obj[groupName]].push(obj);
return rtnObj;
}, {} // initial value to reduce
);
return Object.keys(collect).sort().map(key => collect[key]);
};
const sortRank = function (arrOfRankArrs, rankName) {
return arrOfRankArrs.map(item => item.sort((a, b) => {
if (a[rankName] > b[rankName]) { return -1; }
if (a[rankName] < b[rankName]) { return 1; }
return 0;
}));
};
function topRankPerGroup(n, data, groupName, rankName) {
if (n < 0) { return; }
return sortRank(collectDept(data, groupName),
rankName).map(list => list.slice(0, n));
}
```