Count number of times a string is repeated in array using Lodash

Question

I have an array of strings which are tags of blog posts from database.

This is the example end result of a query :

["apple","banana", "apple", "orange","grapes","mango","banana"];

I need to know how many times a string is repeated in that array so I can build a sort of tag cloud.

Final end result should look like: [{name:"apple",count:2}, {name:"banana", count:2}, {name: "orange",count:1} ...];

I am using lodash in my project and would like to use it if possible. plain javascript is also fine.

klugjo · Accepted Answer · 2018-01-17 06:53:41Z

10

You can use groupBy to do the heavy lifting then use map to format the result to your liking:

const data = ["apple", "banana", "apple", "orange", "grapes", "mango", "banana"];

const result = _.values(_.groupBy(data)).map(d => ({name: d[0], count: d.length}));

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

answered Jan 17, 2018 at 6:53

klugjo

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Comments

gurvinder372 · Accepted Answer · 2018-01-17 06:49:32Z

2

Use reduce and map

var input = ["apple","banana", "apple", "orange","grapes","mango","banana"];

var map = input.reduce( (a,c) => ( a[c] = a[c] || 0, a[c]++, a ) ,{});

var output = Object.keys( map ).map( s => ({name: s, count:map[s]}) );

Demo

var input = ["apple", "banana", "apple", "orange", "grapes", "mango", "banana"];

var map = input.reduce((a, c) => (a[c] = a[c] || 0, a[c]++, a), {});

var output = Object.keys(map).map(s => ({
  name: s,
  count: map[s]
}));

console.log(output);

answered Jan 17, 2018 at 6:49

gurvinder372

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1 Comment

Koder Over a year ago

Your answer is correct, however @klugjo's answer is more readable.

hasen · Accepted Answer · 2018-01-17 06:47:53Z

0

Create a map, mapping name to count. Loop over the list, for each item, if its' in the map, increment it's count, else set its count to one.

if (tag in map) { map[tag] += 1 }
else { map[tag] = 1 }

Then you can iterate of the map and convert it to a list of objects.

answered Jan 17, 2018 at 6:47

hasen

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Comments

Ori Drori · Accepted Answer · 2018-01-17 07:23:06Z

0

To count use _.countBy(), then transform to requested form, by using _.entries(), and mapping the tuples to objects:

const data = ["apple", "banana", "apple", "orange", "grapes", "mango", "banana"];

const result = _.entries(_.countBy(data)).map(([name, count]) => ({ name, count }));

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

answered Jan 17, 2018 at 7:23

Ori Drori

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