GroupBy with Multiple Columns using Lodash or Underscore in Javascript

Question

Getting Problem while converting JSON structure. My JSON Structure is as below.

const member = [{
    memberId: 4,
    memberName: 'ABC',
    age: 22,
    eventId: 5,
    eventName: 'Dance'
  },
  {
    memberId: 4,
    memberName: 'ABC',
    age: 22,
    eventId: 6,
    eventName: 'Music'
  },
  {
    memberId: 4,
    memberName: 'ABC',
    age: 22,
    eventId: 7,
    eventName: 'FootBall'
  },
  {
    memberId: 5,
    memberName: 'PQR',
    age: 24,
    eventId: 6,
    eventName: 'Music'
  },
  {
    memberId: 5,
    memberName: 'PQR',
    age: 24,
    eventId: 5,
    eventName: 'Dance'
  },
]

Here I have two members with associated events. And I want to convert JSON as follows.

const member = [
  {
    memberId: 4,
    memberName: 'ABC',
    age: 22,
    events: [
      {
        id: 5,
        name: 'Dance'
      },
      {
        id: 6,
        name: 'Music'
      },
      {
        id: 7,
        name: 'FootBall'
      }
    ]
  },
  {
    memberId: 5,
    memberName: 'PQR',
    age: 24,
    events: [
      {
        id: 6,
        name: 'Music'
      },
      {
        id: 5,
        name: 'Dance'
      }
    ]
  }
]

I tried creating the structure using below code but it doesn't provide as the desired output. It just creates two Key-Value pair.

var result = _.chain(member)
            .groupBy("memberId")
            .pairs()
            .map(function(currentItem) {
                return _.object(_.zip(["memberId", "events"], currentItem));
            })
            .value();

I don't know how to add other values of JSON in the hierarchy.

Ori Drori · Accepted Answer · 2019-07-27 21:29:41Z

1

After you group the items, map them. Take the 1st item of each group, and remove the event properties, and spread it. To get the the events data, map the group's items and take only the relevant event properties:

const member = [{"memberId":4,"memberName":"ABC","age":22,"eventId":5,"eventName":"Dance"},{"memberId":4,"memberName":"ABC","age":22,"eventId":6,"eventName":"Music"},{"memberId":4,"memberName":"ABC","age":22,"eventId":7,"eventName":"FootBall"},{"memberId":5,"memberName":"PQR","age":24,"eventId":6,"eventName":"Music"},{"memberId":5,"memberName":"PQR","age":24,"eventId":5,"eventName":"Dance"}]

const result = _(member)
  .groupBy('memberId')
  .map(group => ({
    ..._.omit(_.head(group), ['eventId', 'eventName']),
    events: _.map(group, o => ({ id: o.eventId, name: o.eventName }))
  }))
  .value();
  
console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.js"></script>

And the same solution using underscore:

const member = [{"memberId":4,"memberName":"ABC","age":22,"eventId":5,"eventName":"Dance"},{"memberId":4,"memberName":"ABC","age":22,"eventId":6,"eventName":"Music"},{"memberId":4,"memberName":"ABC","age":22,"eventId":7,"eventName":"FootBall"},{"memberId":5,"memberName":"PQR","age":24,"eventId":6,"eventName":"Music"},{"memberId":5,"memberName":"PQR","age":24,"eventId":5,"eventName":"Dance"}]

const result = _.chain(member) // <- change for underscore 
  .groupBy('memberId')
  .map(group => ({
    ..._.omit(_.head(group), ['eventId', 'eventName']),
    events: _.map(group, o => ({ id: o.eventId, name: o.eventName }))
  }))
  .value();
  
console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore.js"></script>

edited Jul 27, 2019 at 21:29

answered Jul 27, 2019 at 21:08

Ori Drori

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3 Comments

Khilen Maniyar Over a year ago

Thanks for the answer, but when I try in my code of Angular, I'm getting an error of "underscore__WEBPACK_IMPORTED_MODULE_2__(...).groupBy(...).map is not a function" so is anything missed.

Ori Drori Over a year ago

You might be using underscore instead of lodash, or you might have a problem with the way you bundle stuff. It's not really related to the question, nor the answer. Does the answer do what you want?

Khilen Maniyar Over a year ago

Is it possible to perform this using underscore?

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