Javascript - Counting duplicates in array of object with many fields in es6

Question

I have object array like this.

const array = [ { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 12 } ]

I want to count duplicates objects and store the count as new object field.

I found this snippet and it work great but it not exactly what i need.

const names = [{  _id: 1 }, { _id: 1}, { _id: 2}, { _id: 1}]

    const result = [...names.reduce( (mp, o) => {
    if (!mp.has(o._id)) mp.set(o._id, Object.assign({ count: 0 }, o));
    mp.get(o._id).count++;
    return mp;
    }, new Map).values()];

    console.log(result);

It works with object with one field _id. In my case there are two, x and y

How should I modify that code?

In brief...I would like to receive the result:

result = [ { x: 1, y: 2, count:3 }, { x: 3, y: 4, count:2 }, { x: 3, y: 12, count:1 } ]

Answer 1

You can use Object.values() and reduce() methods to return new array of objects.

 const array = [ { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 12 } ] const result = Object.values(array.reduce((r, e) => { let k = `${ex}|${ey}`; if(!r[k]) r[k] = {...e, count: 1} else r[k].count += 1; return r; }, {})) console.log(result) 

Here is the solution with Map and spread syntax ...

 const array = [ { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 12 } ] const result = [...array.reduce((r, e) => { let k = `${ex}|${ey}`; if(!r.has(k)) r.set(k, {...e, count: 1}) else r.get(k).count++ return r; }, new Map).values()] console.log(result) 

Answer 2

One way to do it would be to create an index mapping both x and y to the result entry:

 let index = { }; let result = [ ]; const array = [ { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 4 }, { x: 1, y: 2 }, { x: 3, y: 12 } ]; array.forEach(point => { let key = '' + point.x + '||' + point.y; if (key in index) { index[key].count++; } else { let newEntry = { x: point.x, y: point.y, count: 1 }; index[key] = newEntry; result.push(newEntry); } }); console.log(result);