Steve K Steve K - 4 months ago 6x
Javascript Question

Using Lodash, how can I transform this data to the desired format?

I'm fairly new to lodash and suspect that it can help me transform my data in the way I want. I've been reading the lodash docs but to be honest it's not sinking in, I'm not seeing the correct combination of operations I need.

Here is what I want to do:

var configs = [ {
configId: 1,
options: [ {categoryId: 1, id: 100},
{categoryId: 2, id: 200},
{categoryId: 3, id: 300} ] },
configId: 2,
options: [ {categoryId: 1, id: 105},
{categoryId: 2, id: 210} ] },
configId: 3,
options: [ {categoryId: 2, id: 200},
{categoryId: 1, id: 165},
{categoryId: 3, id: 300} ] }

// I want the above to look like this:
[ {categoryId: 1, ids: [100, 105, 165]},
{categoryId: 2, ids: [200, 210]},
{categoryId: 3, ids: [300]} ]

And here is a fiddle if you want to experiment.

When I look at the problem I think I want to:

  1. Combine all the
    objects so I have one big array of

  2. Group by

  3. And then I really lose my way... I suspect I could use reduce() here, but then I also think I need a map() to actually produce the transformed object.

Anyway, I'm looping on this and not making progress, I'm hoping someone can point me the right direction.


With ES2015 Syntax:
  _.groupBy(_.flatMap(configs, config => config.options), 'categoryId'), 
  (val, key) => ({categoryId: key, ids: _.uniq(, v => })

ES5 compatible (generated by Babel):
    _.flatMap(configs, function (config) {
    return config.options;
  function (val, key) {
    return {
        categoryId: key,
        ids: _.uniq(, function (v) {


_.flatMap(configs, config => config.options)

Takes options array from each configs object, flattens them into a single array of [{categoryId: xx, id: yy}, ...]

_.groupBy(..., 'categoryId')

Groups above array by their categoryId, as [{xx: [categoryId: xx, id: yy}, ...], (val, key) => ({categoryId: key, ids: _.uniq(, v => }))

Receives val = [{xx: [categoryId: xx, id: yy}, ...], key: xx and maps them to object where categoryId is set to received key, and ids to array of unique ids from grouped objects. Result is the array you wanted.