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---
id: 595011cba5a81735713873bd
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title: Top rank per group
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challengeType: 5
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forumTopicId: 302339
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dashedName: top-rank-per-group
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---
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# --description--
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Find the top `n` ranked data in each group, where `n` is provided as a parameter. Name of the rank and the group are also provided as parameter.
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Given the following data:
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```js
testData1 = [
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{ 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' }
];
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```
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One could rank top 10 employees in each department by calling:
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```js
topRankPerGroup(10, testData1, 'dept', 'salary')
```
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Given the following data:
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```js
testData2 = [
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{ 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 }
];
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```
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One could rank the top-rated movie in each genre by calling:
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```js
topRankPerGroup(1, testData2, 'genre', 'rating')
```
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The function should return an array with an array for each group containing the top `n` objects.
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For example, given data:
```js
[
{ name: 'Claire Buckman', id: 'E39876', salary: 27800, dept: 'D101' },
{ name: 'Rich Holcomb', id: 'E01234', salary: 49500, dept: 'D050' },
{ name: 'David Motsinger', id: 'E27002', salary: 19250, dept: 'D050' },
{ name: 'Tim Sampair', id: 'E03033', salary: 27000, dept: 'D101' },
{ name: 'Kim Arlich', id: 'E10001', salary: 57000, dept: 'D050' },
{ name: 'Timothy Grove', id: 'E16398', salary: 29900, dept: 'D101' }
];
```
Top two ranking employees in each department by salary would be:
```js
[ [ { name: 'Kim Arlich', id: 'E10001', salary: 57000, dept: 'D050' },
{ name: 'Rich Holcomb', id: 'E01234', salary: 49500, dept: 'D050' } ],
[ { name: 'Timothy Grove', id: 'E16398', salary: 29900, dept: 'D101' },
{ name: 'Claire Buckman', id: 'E39876', salary: 27800, dept: 'D101' } ] ]
```
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# --hints--
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`topRankPerGroup` should be a function.
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```js
assert(typeof topRankPerGroup === 'function');
```
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`topRankPerGroup` should return undefined on negative n values.
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```js
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assert(typeof topRankPerGroup(-1, []) === 'undefined');
```
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For `topRankPerGroup(10, testData1, 'dept', 'salary')` , the first result in the first group should be `{ name: 'John Rappl', id: 'E21437', salary: 47000, dept: 'D050'}` .
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```js
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assert.deepEqual(res1[0][0], { name: 'John Rappl', id: 'E21437', salary: 47000, dept: 'D050'});
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```
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For `topRankPerGroup(10, testData1, 'dept', 'salary')` , the last result in the last group should be `{ name: 'Adam Smith', id: 'E63535', salary: 18000, dept: 'D202' }` .
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```js
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assert.deepEqual(res1[3][3], { name: 'Adam Smith', id: 'E63535', salary: 18000, dept: 'D202' });
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```
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`topRankPerGroup(1, ...)` should return only top ranking result per group.
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```js
assert.equal(res2[2].length, 1);
```
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`topRankPerGroup(2, ...)` should return two ranking results per group.
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```js
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assert.equal(res3[2][1].name, 'Maze Runner');
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```
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# --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;
}
```
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# --solutions--
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```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));
}
```