How to transform array of objects into nested array groups

Question

Example data:

var people = [
  { name: 'John', age: 30, gender: 'male' },
  { name: 'Kelly', age: 31, gender: 'female' },
  { name: 'Stephanie', age: 30, gender: 'female' },
  { name: 'Dan',  age: 28, gender: 'male' },
  { name: 'Crystal', age: 29, gender: 'female' }
];

I'm trying to group together an array of objects based on a property of the objects. I attempted using _.groupBy, but that returns an object and not an array. Is there a similar function that can transform into the below result?

Desired result

var newPeople = [
  [
    { name: 'John', age: 30, gender: 'male' },
    { name: 'Dan',  age: 28, gender: 'male' }
  ],
  [
    { name: 'Kelly', age: 31, gender: 'female' },
    { name: 'Stephanie', age: 30, gender: 'female' },
    { name: 'Crystal', age: 29, gender: 'female' }
  ]
];

Nenad Vracar · Accepted Answer · 2017-10-21 17:41:24Z

3

You can use groupBy and then values and get array of arrays.

var people = [
  { name: 'John', age: 30, gender: 'male' },
  { name: 'Kelly', age: 31, gender: 'female' },
  { name: 'Stephanie', age: 30, gender: 'female' },
  { name: 'Dan',  age: 28, gender: 'male' },
  { name: 'Crystal', age: 29, gender: 'female' }
];

var result = _.values(_.groupBy(people, 'gender'))
console.log(result)

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

edited Oct 21, 2017 at 17:41

answered Oct 21, 2017 at 17:30

Nenad Vracar

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1 Comment

Deepak Acharya Over a year ago

If we have multiple array of keys in groupBy then how will we achieve this?

Gruff Bunny · Accepted Answer · 2017-10-21 21:26:06Z

2

Instead of groupBy you could use lodash's partition:

let result = _.partition(people, {gender: 'male'})

or to have them in seperate variables, add a dash of destructuring:

let [males, females] = _.partition(people, {gender: 'male'})

answered Oct 21, 2017 at 21:26

Gruff Bunny

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Comments

Nina Scholz · Accepted Answer · 2017-10-21 17:45:44Z

1

You could use an object for the groups and iterate the array while using the group for pushing.

var people = [{ name: 'John', age: 30, gender: 'male' }, { name: 'Kelly', age: 31, gender: 'female' }, { name: 'Stephanie', age: 30, gender: 'female' }, { name: 'Dan',  age: 28, gender: 'male' }, { name: 'Crystal', age: 29, gender: 'female' }],
    groups = Object.create(null),
    newPeople = [];
    
people.forEach(function (o) {
    if (!groups[o.gender]) {
        groups[o.gender] = [];
        newPeople.push(groups[o.gender]);
    }
    groups[o.gender].push(o);
});

console.log(newPeople);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Oct 21, 2017 at 17:45

Nina Scholz

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Comments

guest271314 · Accepted Answer · 2017-10-21 17:51:05Z

1

You can use Set to get unique "gender" properties, .Array.from() and .filter() to create an array of arrays of results of filtered matches

var people = [
  { name: 'John', age: 30, gender: 'male' },
  { name: 'Kelly', age: 31, gender: 'female' },
  { name: 'Stephanie', age: 30, gender: 'female' },
  { name: 'Dan',  age: 28, gender: 'male' },
  { name: 'Crystal', age: 29, gender: 'female' }
];


let res = Array.from(new Set(people.map(({gender}) => gender))
          , g => people.filter(({gender}) => gender === g));

console.log(res);

edited Oct 21, 2017 at 17:51

answered Oct 21, 2017 at 17:43

guest271314

1

Comments

score 1 · Accepted Answer · 2017-10-21 19:26:14Z

1

Why not use a good old for loop ?

var groups = {};
var newPeople = [];
var people = [
  { name: 'John', age: 30, gender: 'male' },
  { name: 'Kelly', age: 31, gender: 'female' },
  { name: 'Stephanie', age: 30, gender: 'female' },
  { name: 'Dan',  age: 28, gender: 'male' },
  { name: 'Crystal', age: 29, gender: 'female' }
];
for (let i = 0; i < people.length; i++) {
  let gender = people[i]["gender"];
  if (!groups[gender]) groups[gender] = [];
  groups[gender].push(people[i]);
}
for (let gender in groups) {
  newPeople.push(groups[gender]);
}
console.log(newPeople);

edited Oct 21, 2017 at 19:26

answered Oct 21, 2017 at 19:04

user1636522

1 Comment

myLogicIsWrong Over a year ago

nice! I agree, it could be, and maybe should be, a for loop. However, my project already included lodash and I figured, why not leverage?

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