JavaScript array of objects grouping based on key and value

Question

let data =  [
{news: id1, users: [{user1}, {user2}, {user3}]},
{news: id2, users: [{user2}, {user4}, {user6}]},
{news: id3, users: [{user1}, {user2}, {user4}]}
]

So from the above data, I need to be able to group news items to form a template(let's consider a template consists strictly two news items). Then for every template, I need to match the corresponding user. Finally, when I'm done with creating all the templates I need to map remaining users to their respective news items.

I've added a sample output below

[id1,id2] : [user2]
[id2, id3] : [user2, user4]
[id3, id1] : [user1, user2]
[id2] : [user6]
[id1] : [user3]

How do I achieve this?

Question is not clear. Are you trying to create all the combinations ? — Viswanath Lekshmanan
– Viswanath Lekshmanan, Commented Dec 10, 2019 at 14:39
Please provide a minimal reproducible example not pseudo-data — Jamiec
– Jamiec, Commented Dec 10, 2019 at 14:40
why doesn't [id3] : [] exist and have a value in your result example? Is it because it does not have a distinct value? — Ivan86
– Ivan86, Commented Dec 10, 2019 at 14:42
@ViswanathLekshmanan, yes, it's actually a 3C2 combination on news, but that doesn't include all the users, so I need to pick up the remaining users and map them to their respective news items. — shashwat_k
– shashwat_k, Commented Dec 10, 2019 at 14:45
@Ivan86, that's because I'm grouping news as templates and every template contains exactly 2 news items. But for the remaining users, I need to map them to their respective news items — shashwat_k
– shashwat_k, Commented Dec 10, 2019 at 14:47

Nina Scholz · Accepted Answer · 2019-12-11 09:39:26Z

3

You could take a hash table and build the wanted structure by checking the length of the values and if greater than 2 take the combination of the values for adding the new grouups to the result set, instead of the given group.

var data = [{ news: 'id1', users: ['user1', 'user2', 'user3'] }, { news: 'id2', users: ['user2', 'user4', 'user6'] }, { news: 'id3', users: ['user1', 'user2', 'user4'] }],
    cool = data.reduce((r, { news, users }) => users.reduce((o, user) => ((o[user] = o[user] || []).push(news), o), r), {}),
    result = Object.entries(cool).reduce((r, [user, news]) => {
        function add(k, v) {
            var temp = r.find(([a]) => a.join('|') === v.join('|'));
            if (!temp) r.push(temp = [v, []]);
            temp[1].push(k);
        }

        if (news.length > 2) {
            news.reduce((r, v, i, a) => r.concat(a.slice(i + 1).map(w => [v, w])), [])
                .forEach(news => add(user, news));
        } else {
            add(user, news);
        }
        return r;
    }, []);

console.log(result);

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

edited Dec 11, 2019 at 9:39

answered Dec 10, 2019 at 16:00

Nina Scholz

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2 Comments

Ivan86 Over a year ago

Very nice. +2 if I could.

shashwat_k Over a year ago

Wow, this is precisely what I wanted, I need to clearly look into the solution. Because although I said that a template would contain 2 elements, it's actually 10 and the remaining users will end up with < 10 news items. Could be ranging anywhere between 0 and 9. Thank you very much!!

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