Reduce array of results in to array of objects with sums and user id

Question

I am attempting to take an array of results and reduce them into a single array.

The data is:

const data = [
    { profileid: '1', points: 25, winner: true },
    { profileid: '2', points: 15, winner: false },
    { profileid: '3', points: 18, winner: false },
    { profileid: '1', points: 15, winner: true },
    { profileid: '2', points: 18, winner: false },
    { profileid: '3', points: 25, winner: false },
]

I am attempting to sum up all points by userid (I have achieved this) and also sum up the amount of times winner === true in each object

Expected Results

[
    { profileid: '1', points: 40, wins: 1 },
    { profileid: '2', points: 33, wins: 0 },
    { profileid: '3', points: 43, wins: 1 },
]

Currently I am unable to talley the sum of "true" results in each object. Additionally I am returning an object instead of an array.

Snippet

const data = [
    { profileid: '1', points: 25, winner: true },
    { profileid: '2', points: 15, winner: false },
    { profileid: '3', points: 18, winner: false },
    { profileid: '1', points: 15, winner: false },
    { profileid: '2', points: 18, winner: false },
    { profileid: '3', points: 25, winner: true },
]

const result = data.reduce((acc, cur) => ({
            ...acc,
            [cur.profileid]: {
                profileid: cur.profileid,
                points: cur.points + (acc[cur.profileid] ? acc[cur.profileid].points : 0),
                wins: cur.winner
                    ? acc[cur.profile]
                        ? acc[cur.profile].wins + 1
                        : 0
                    : acc[cur.profile]
                    ? acc[cur.profile].wins
                    : 0,
            },
        }),
        []
    )
    
console.log(result)

Does this answer your question? Javascript group by array field and reduce — derpirscher
– derpirscher, Commented Aug 27, 2021 at 16:07

0stone0 · Accepted Answer · 2021-08-27 16:29:09Z

Applying the same logic for the points can give something like:

wins: cur.winner ? ((acc[cur.profileid]?.wins || 0) + 1) : (acc[cur.profileid]?.wins || 0),

Were we start by checking if the current winner is true

If so, add 1 (|| 0) for the first time where wins doesn't exist
If not, just use acc[cur.profileid]?.wins (also a fallback if the first time is false)

const data = [
    { profileid: '1', points: 25, winner: true },
    { profileid: '2', points: 15, winner: false },
    { profileid: '3', points: 18, winner: false },
    { profileid: '1', points: 15, winner: false },
    { profileid: '2', points: 18, winner: false },
    { profileid: '3', points: 25, winner: true },
]

const result = data.reduce((acc, cur) => ({
        ...acc,
        [cur.profileid]: {
            wins: cur.winner ? ((acc[cur.profileid]?.wins || 0) + 1) : (acc[cur.profileid]?.wins || 0),
            profileid: cur.profileid,
            points: cur.points + (acc[cur.profileid] ? acc[cur.profileid].points : 0),
        },
    }),
    []
)
    
console.log(result)

That said, I'd personally prefer a simple for and a single if to get a more readable code:

Please consider this example:

Create empty result obj
Loop over each obj in the data array
Create empty obj in data if needed
Bump the points and wins values

const data = [
    { profileid: '1', points: 25, winner: true },
    { profileid: '2', points: 15, winner: false },
    { profileid: '3', points: 18, winner: false },
    { profileid: '1', points: 15, winner: false },
    { profileid: '2', points: 18, winner: false },
    { profileid: '3', points: 25, winner: true },
];
const result = {};

for (let i in data) {
  
    // Create current profileId object
    if (!result[data[i].profileid]) {
        result[data[i].profileid] = {
            wins: 0,
            points: 0,
            profileid: +data[i].profileid
        };
    }

    // Bump points/wins values
    result[data[i].profileid].points += data[i].points;
    result[data[i].profileid].wins += +data[i].winner;
}

console.log(result);

zb22 · Accepted Answer · 2021-08-28 10:24:25Z

You can sum the wins the same way as you sum the points:

const data = [
    { profileid: '1', points: 25, winner: true },
    { profileid: '2', points: 15, winner: false },
    { profileid: '3', points: 18, winner: false },
    { profileid: '1', points: 15, winner: true },
    { profileid: '2', points: 18, winner: false },
    { profileid: '3', points: 25, winner: true },
]

const result = data.reduce((acc, cur) => ({
            ...acc,
            [cur.profileid]: {
                profileid: cur.profileid,
                points: cur.points + (acc[cur.profileid] ? acc[cur.profileid].points : 0),
                wins: cur.winner + (acc[cur.profileid] ? acc[cur.profileid].wins : 0)
            },
        }),
        []
    )
    
console.log(result)

You can also simplify wins like this:
wins: !!(acc[cur.profileid]?.wins) + cur.winner

In case acc[cur.profileid]?.wins returns undefined,
you can convert it to a Boolean by !! or Boolean() to avoid getting NaN

Boolean
Optional chaining (?.)

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