Lodash create collection from duplicate object keys

Question

I have the following structure:

var output = [{
    "article": "BlahBlah",
    "title": "Another blah"
}, {
    "article": "BlahBlah",
    "title": "Return of the blah"
}, {
    "article": "BlahBlah2",
    "title": "The blah strikes back"
}, {
    "article": "BlahBlah2",
    "title": "The blahfather"
}]

From the above using an elegant lodash one-liner, I need to create the following structure.

var newOutput = [{
    "article": "BlahBlah",
    "titles": ["Another blah", "Return of the blah"]
}, {
   "article": "BlahBlah2",
   "titles": ["The blah strikes back", "The blahfather"]
}]

Help as always, is greatly appreciated.. A huge plus for an explanation for how a solution would work.

titles should be array if there is only one record?

Tushar
– Tushar

2016-07-18 13:59:45 +00:00
Commented Jul 18, 2016 at 13:59 — Tushar
– Tushar, Commented Jul 18, 2016 at 13:59
is the property really 'title:'?

Nina Scholz
– Nina Scholz

2016-07-18 15:03:47 +00:00
Commented Jul 18, 2016 at 15:03 — Nina Scholz
– Nina Scholz, Commented Jul 18, 2016 at 15:03
@NinaScholz.. well spotted

stackunderflow
– stackunderflow

2016-07-18 16:25:28 +00:00
Commented Jul 18, 2016 at 16:25 — stackunderflow
– stackunderflow, Commented Jul 18, 2016 at 16:25

castletheperson · Accepted Answer · 2016-07-19 12:40:23Z

9

Use _.groupBy and then _.map the resulting object to an array of objects.

var newOutput = _(output)
    .groupBy('article')
    .map(function(v, k){ return { article: k, titles: _.map(v, 'title') } })
    .value();

var output = [{"article":"BlahBlah","title":"Another blah"},{"article":"BlahBlah","title":"Return of the blah"},{"article":"BlahBlah2","title":"The blah strikes back"},{"article":"BlahBlah2","title":"The blahfather"}];

let newOutput = _(output)
    .groupBy('article')
    .map(function(v, k){ return { article: k, titles: _.map(v, 'title') } })
    .value();

console.log(newOutput);

<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>

With ES6 arrow-functions,

var newOutput = _(output)
    .groupBy('article')
    .map((v, k) => ({ article: k, titles: _.map(v, 'title') }))
    .value();

edited Jul 19, 2016 at 12:40

answered Jul 19, 2016 at 6:15

castletheperson

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1 Comment

amd Over a year ago

You have missing the .value() resolver to resolve the chain, otherwise you'll get a LodashWrapper instead of the needed value, +1 for the nice approach

amd · Accepted Answer · 2016-07-19 06:22:35Z

3

A better lodash version could be (using the awesome chaining approach)

_(a).groupBy('article').map( (x,k) => ({ article: k, titles:_.map(x, 'title')}) ).value();

If you want to group by article (so article would be the key, useful for quick lookup)

_(a).groupBy('article').mapValues(x => _.map(x, 'title')).value();

answered Jul 19, 2016 at 6:22

amd

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3 Comments

castletheperson Over a year ago

Isn't this the same answer? You added an arrow function to the solution, but otherwise only the second part of your answer is new.

amd Over a year ago

@4castle actually I didn't check yours, but your original answer was a little different, (I think u've used _.chain), even now your's is not correct, since you have missing the .value() resolver at the end

castletheperson Over a year ago

It's working correctly, but I was also under the impression that .value() was only needed if .chain() was used. That's why I switched to the constructor.

Nina Scholz · Accepted Answer · 2016-07-18 16:31:20Z

2

A proposal in plain Javascript

It uses a IIFE (Immediate Invoked Function Expression) for using private variables and for collecting the return values in an array.

Beside that it uses a hash table for the reference to the right array item.

var output = [{ article: "BlahBlah", title: "Another blah" }, { article: "BlahBlah", title: "Return of the blah" }, { article: "BlahBlah2", title: "The blah strikes back" }, { article: "BlahBlah2", title: "The blahfather" }],
    newOutput = function (data) {
        var r = [];
        data.forEach(function (a) {
            if (!this[a.article]) {
                this[a.article] = { article: a.article, titles: [] };
                r.push(this[a.article]);
            }
            this[a.article].titles.push(a.title);
        }, Object.create(null));
        return r;
    }(output);
        
console.log(newOutput);

edited Jul 18, 2016 at 16:31

answered Jul 18, 2016 at 15:03

Nina Scholz

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1 Comment

stackunderflow Over a year ago

Thank you, although a lodash example would be great. Just to keep it brief.

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