Lo-Dash array grouping

Question

I spent hours on the Lo-Dash documentation site now, and can't find a solution for my problem. I don't know how it's called, so it is a bit hard to search for. I basically want to group an array into an object so that duplicate entries are a field while different entries are an array.

For example, I have this array:

var characters = [
  { 'name': 'barney', 'age': 42,  'pet': 'dog' },
  { 'name': 'fred',   'age': 35,  'pet': 'dog' },
  { 'name': 'barney', 'age': 42,  'pet': 'cat' },
  { 'name': 'fred',   'age': 35,  'pet': 'goldfish' }
];

And I want to get this:

[
  { name: 'barney',
    age: 42,
    pet: [ 'dog', 'cat' ] },
  { name: 'fred',
    age: 35,
    pet: [ 'dog', 'goldfish' ] }
]

Is there a Lo-Dash method for doing this, or do I have to chain several ones? What is the best way to achieve this?

Answer 1

Although answered, still a try. JSFIDDLE

var characters = [
      { 'name': 'barney', 'age': 42,  'pet': 'dog' },
      { 'name': 'fred',   'age': 35,  'pet': 'dog' },
      { 'name': 'barney', 'age': 42,  'pet': 'cat' },
      { 'name': 'fred',   'age': 35,  'pet': 'goldfish' }
    ];

var result=_.chain(characters).groupBy("name").map(function(v, i) {
      return {
        name: i,
        age: _.get(_.find(v, 'age'), 'age'),
        pet: _.map(v, 'pet')
      }
    }).value();

document.body.innerHTML = '<pre>' + JSON.stringify(result, null, '  ') + '</pre>';

Answer 2

Here a more lo-dash, underscore way of doing it:

var result = _.reduce(characters, function (prev, current) {
    var char = _.find(prev, function (character) {
        return character['name'] === current['name'];
    });

    // Character does not yet exists in the array, push it
    if (char === undefined) {
        prev.push(current);
    } else {
        // If char['pet'] is not an array, create one
        if (!_.isArray(char['pet'])) {
            char['pet'] = [char['pet']];
        }

        // Push the current pets to the founded character
        char['pet'].push(current['pet']);
    }

    return prev;
}, []); // Initialize an empty array for the prev object

console.log(result);

Let me know if there is a more awesomeness feature in underscore/lodash :-)!

Fiddle

Answer 3

Here's a more elegant and much shorter solution, with chaining:

var characters = [{
    'name': 'barney',
    'age': 42,
    'pet': 'dog'
}, {
    'name': 'fred',
    'age': 35,
    'pet': 'dog'
}, {
    'name': 'barney',
    'age': 42,
    'pet': 'cat'
}, {
    'name': 'fred',
    'age': 35,
    'pet': 'fish'
}];

var result = _(characters).groupBy('name').transform(function(result, current) {
    result.push({
        name: current[0].name,
        age: current[0].age,
        pets: _.map(current, 'pet')
    });
}, []).value();

document.write('<pre>' + JSON.stringify(result, null, '\t') + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.js"></script>