Grouping by using lodash

Question

I have an array of objects as follows:

var data = [
  {
    "count": 1, 
    "make": "ALFA ROMEO", 
    "model": "GIULIETTA DIESEL - 2010"
  }, 
  {
    "count": 2, 
    "make": "AUDI", 
    "model": "A1 DIESEL"
  }, 
  {
    "count": 1, 
    "make": "AUDI", 
    "model": "A1 SPORTBACK DIESEL"
  }, 
  {
    "count": 2, 
    "make": "AUDI", 
    "model": "A3 DIESEL - 2012"
  }, 
  {
    "count": 3, 
    "make": "Volkswagen", 
    "model": "Golf"
  }, 
  {
    "count": 3, 
    "make": "Ford", 
    "model": "Escord"
  }, 
  {
    "count": 2, 
    "make": "Opel", 
    "model": "Zafira"
  }
]

I want to group by it by make and then get three makes with the highest count and the rest I will to show as other.

For example I want to get:

var result = [
    {
       "brand": "Audi",
       "count": 5
     },
     {
       "brand": "Volkswagen",
       "count": 3
     },
     {
       "brand": "Ford",
       "count": 3
     },
     {
       "brand": "Other",
       "count": 3
     }
]

I have no idea how to start. Any help?

Possible duplicate of [How to group or merge this array of objects in javascript?](https://stackoverflow.com/questions/46664213/how-to-group-or-merge-this-array-of-objects-in-javascript) — Faly, Nov 21 '17 at 14:17
Some good places to start: https://stackoverflow.com/questions/11582284/using-underscore-groupby-to-group-an-array-of-cars-by-their-colour and https://lodash.com/docs/4.17.4#groupBy — Phillip Thomas, Nov 21 '17 at 14:21
Duplicate of https://stackoverflow.com/questions/45744591/underscore-sortby-groupby-with-count-of-grouped-arrays?rq=1 — Phillip Thomas, Nov 21 '17 at 14:22

Ori Drori · Accepted Answer · 2017-11-21T14:59:51.077

Using lodash

Start a lodash chain. Use _.groupBy() by the make, then _.map() the results, and _.sumBy() the count properties. Convert back to an array using _.values(), sort descending with _.orderBy(), and use _.value() to finish the chain. Split the results into 2 arrays, and sum the 2nd array (the lowset counts) using reduce:

var data = [{"count":1,"make":"ALFA ROMEO","model":"GIULIETTA DIESEL - 2010"},{"count":2,"make":"AUDI","model":"A1 DIESEL"},{"count":1,"make":"AUDI","model":"A1 SPORTBACK DIESEL"},{"count":2,"make":"AUDI","model":"A3 DIESEL - 2012"},{"count":3,"make":"Volkswagen","model":"Golf"},{"count":3,"make":"Ford","model":"Escord"},{"count":2,"make":"Opel","model":"Zafira"}];

var counts = _(data)
  .groupBy('make')
  .map(function(g, key) { return {
      make: key,
      count: _.sumBy(g, 'count')
  };})
  .values()
  .orderBy('count', 'desc')
  .value();
  
var result = counts.slice(0, 3).concat({
  brand: 'other',
  count: counts.slice(3).reduce(function(s, { count }) { return s + count; }, 0)
})
  
console.log(result);

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

Using ES6

Iterate with Array#reduce, collect all the make count values to an object in a Map, then get the map values iterator, and spread to get an array, and sort descending. Split the results into 2 arrays, and sum the 2nd array (the lowset counts) using reduce:

const data = [{"count":1,"make":"ALFA ROMEO","model":"GIULIETTA DIESEL - 2010"},{"count":2,"make":"AUDI","model":"A1 DIESEL"},{"count":1,"make":"AUDI","model":"A1 SPORTBACK DIESEL"},{"count":2,"make":"AUDI","model":"A3 DIESEL - 2012"},{"count":3,"make":"Volkswagen","model":"Golf"},{"count":3,"make":"Ford","model":"Escord"},{"count":2,"make":"Opel","model":"Zafira"}];

const counts = [...data.reduce((m, { make, count }) => {
  const item = m.get(make) || { make, count: 0 };
  
  item.count += count;

  return m.set(make,  item);
}, new Map()).values()].sort((a, b) => b.count - a.count);

const result = counts.slice(0, 3).concat({
  brand: 'other',
  count: counts.slice(3).reduce((s, { count }) => s + count, 0)
})

console.log(result);

score 3 · Answer 2 · answered Nov 21 '17 at 14:42

You can achive that with combination of lodash groupBy and sumBy

var result = _.chain(data)
        .groupBy("make")
        .map( (element, id) => ({
            make: id,
            count: _.sumBy(element, 'count'),
        }))
        .value();

console.log(result);

[
  {
    "make": "ALFA ROMEO",
    "count": 1
  },
  {
    "make": "AUDI",
    "count": 5
  },
  {
    "make": "Volkswagen",
    "count": 3
  },
  {
    "make": "Ford",
    "count": 3
  },
  {
    "make": "Opel",
    "count": 2
  }
]

Nina Scholz · Answer 3 · 2017-11-21T14:47:48.883

With plain Javascript, you could take a hash table for collecting same make and sort the result array. Later add all counts which are at the end of the result set until the array gets a wanted length.

var data = [{ count: 1, make: "ALFA ROMEO", model: "GIULIETTA DIESEL - 2010" }, { count: 2, make: "AUDI", model: "A1 DIESEL" }, { count: 1, make: "AUDI", model: "A1 SPORTBACK DIESEL" }, { count: 2, make: "AUDI", model: "A3 DIESEL - 2012" }, { count: 3, make: "Volkswagen", model: "Golf" }, { count: 3, make: "Ford", model: "Escord" }, { count: 2, make: "Opel", model: "Zafira" }],
    hash = Object.create(null),
    result = [];

data.forEach(function (car) {
    if (!hash[car.make]) {
        hash[car.make] = { make: car.make, count: 0 };
        result.push(hash[car.make]);
    }
    hash[car.make].count += car.count;
});

result.sort(function (a, b) {
    return b.count - a.count;
});

while (result.length > 4) {
    result.push({ make: 'Other', count: result.pop().count + result.pop().count });
}

console.log(result);

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Grouping by using lodash

3 Answers3

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