Different ways to leverage the countBy and filter functions in lodash

Question

Different ways to leverage the countBy and filter functions in lodash

Here is a data array that I am working with:

const data = [
  { year: 1900, title: 'test 1' },
  { year: 2000, title: 'test 2' },
  { year: 2000, title: 'test 3' },
  { year: 2000, title: 'test 4' },
];

My goal is to create an array of years where each year appears more than twice:

[2000]

We can easily achieve the countBy using the following code:

_.chain(data)
.countBy('year')
.value()

This will give us the following object:

{'1900': 1, '2000': 3}

I am facing some challenges with the filtering part. When I tried the following code, it returned an empty array:

_.chain(data)
  .countBy('year')
  .filter((o) => {
    o > 2;
  })
  .value();

Can someone guide me on the correct approach?

javascript arrays lodash

Answer 1

Answer №1

Swap out _.filter() for _.pick() since filter will only return the values ([3]), not the keys (the years). Make sure to also include a callback function - o => o > 2. Then, extract an array of the keys (years), and convert them to numbers if necessary.

const data = [{"year":1900,"title":"test 1"},{"year":2000,"title":"test 2"},{"year":2000,"title":"test 3"},{"year":2000,"title":"test 4"}];

const result = _(data)
  .countBy('year')
  .pickBy(o => o > 2)
  .keys()
  .map(Number) // <- if you want the years as numbers
  .value();
  
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js" integrity="sha512-90vH1Z83AJY9DmlWa8WkjkV79yfS2n2Oxhsi2dZbIv0nC4E6m5AbH8Nh156kkM7JePmqD6tcZsfad1ueoaovww==" crossorigin="anonymous"></script>

Answer 2

Swap out _.filter() for _.pick() since filter will only return the values ([3]), not the keys (the years). Make sure to also include a callback function - o => o > 2. Then, extract an array of the keys (years), and convert them to numbers if necessary.

const data = [{"year":1900,"title":"test 1"},{"year":2000,"title":"test 2"},{"year":2000,"title":"test 3"},{"year":2000,"title":"test 4"}];

const result = _(data)
  .countBy('year')
  .pickBy(o => o > 2)
  .keys()
  .map(Number) // <- if you want the years as numbers
  .value();
  
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js" integrity="sha512-90vH1Z83AJY9DmlWa8WkjkV79yfS2n2Oxhsi2dZbIv0nC4E6m5AbH8Nh156kkM7JePmqD6tcZsfad1ueoaovww==" crossorigin="anonymous"></script>

Answer 3

Answer №2

const newData = [
  { century: 1800, name: 'example 1' },
  { century: 1900, name: 'example 2' },
  { century: 2000, name: 'example 3' },
  { century: 2000, name: 'example 4' },
];

const centuryNamesMap = _.groupBy(newData, 'century');
const centuriesWithMoreThanTwoEntries = _.filter(_.keys(centuryNamesMap), century => centuryNamesMap[century].length > 2);

console.log(centuriesWithMoreThanTwoEntries);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js" integrity="sha512-90vH1Z83AJY9DmlWa8WkjkV79yfS2n2Oxhsi2dZbIv0nC4E6m5AbH8Nh156kkM7JePmqD6tcZsfad1ueoaovww==" crossorigin="anonymous"></script>

Answer 4

const newData = [
  { century: 1800, name: 'example 1' },
  { century: 1900, name: 'example 2' },
  { century: 2000, name: 'example 3' },
  { century: 2000, name: 'example 4' },
];

const centuryNamesMap = _.groupBy(newData, 'century');
const centuriesWithMoreThanTwoEntries = _.filter(_.keys(centuryNamesMap), century => centuryNamesMap[century].length > 2);

console.log(centuriesWithMoreThanTwoEntries);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js" integrity="sha512-90vH1Z83AJY9DmlWa8WkjkV79yfS2n2Oxhsi2dZbIv0nC4E6m5AbH8Nh156kkM7JePmqD6tcZsfad1ueoaovww==" crossorigin="anonymous"></script>

Different ways to leverage the countBy and filter functions in lodash

Answer №1

Answer №2

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