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---
title: Averages-Mode
id: 594d8d0ab97724821379b1e6
challengeType: 5
---
## Description
< section id = 'description' >
< p > Write a program to find the < a href = "https://en.wikipedia.org/wiki/Mode (statistics)" title = "wp: Mode (statistics)" > mode< / a > value of a collection.< / p > < p > The case where the collection is empty may be ignored. Care must be taken to handle the case where the mode is non-unique.< / p > < p > If it is not appropriate or possible to support a general collection, use a vector (array), if possible. If it is not appropriate or possible to support an unspecified value type, use integers.< / p >
< / section >
## Instructions
< section id = 'instructions' >
< / section >
## Tests
< section id = 'tests' >
```yml
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tests:
- text: < code > mode</ code > is a function.
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testString: assert(typeof mode === 'function', '< code > mode< / code > is a function.');
- text: < code > mode([1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17])</ code > should equal < code > [6]</ code >
testString: assert.deepEqual(mode(arr1), [6], '< code > mode([1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17])< / code > should equal < code > [6]< / code > ');
- text: < code > mode([1, 2, 4, 4, 1])</ code > should equal < code > [1, 4]</ code > .
testString: assert.deepEqual(mode(arr2).sort(), [1, 4], '< code > mode([1, 2, 4, 4, 1])< / code > should equal < code > [1, 4]< / code > .');
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```
< / section >
## Challenge Seed
< section id = 'challengeSeed' >
< div id = 'js-seed' >
```js
function mode (arr) {
// Good luck!
return true;
}
```
< / div >
### After Test
< div id = 'js-teardown' >
```js
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const arr1 = [1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17];
const arr2 = [1, 2, 4, 4, 1];
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```
< / div >
< / section >
## Solution
< section id = 'solution' >
```js
function mode(arr) {
const counter = {};
let result = [];
let max = 0;
// for (const i in arr) {
arr.forEach(el => {
if (!(el in counter)) {
counter[el] = 0;
}
counter[el]++;
if (counter[el] === max) {
result.push(el);
}
else if (counter[el] > max) {
max = counter[el];
result = [el];
}
});
return result;
}
```
< / section >