Return object(s) in array with highest property value per group

Question

I have an array containing several objects similar to the following:

{person: {name: "Steve", id: 1}, role: 1}
{person: {name: "Phil", id: 2}, role: 1}
{person: {name: "Steve", id: 1}, role: 3}
{person: {name: "Phil", id: 2}, role: 6}

My intention is to return an array of the same type, but I'd like to return only one object per "person" with their highest role.

I understand the following will give me a single object with the highest role.

array.reduce((prev, cur) => prev.role > cur.role ? prev : cur);

How do I return each unique person and their corresponding highest role as a new array?

Like so:

{person: {name: "Steve", id: 1}, role: 3}
{person: {name: "Phil", id: 2}, role: 6}

_.map(_.groupBy(input, 'person.id'), vs => _.maxBy(vs, 'role')) — castletheperson
– castletheperson, Commented Dec 24, 2018 at 15:37

Nina Scholz · Accepted Answer · 2018-12-24 15:30:48Z

4

You need to collect the objects and if you have already one with the same id check the role and take the greater one.

var data = [{ person: { name: "Steve", id: 1 }, role: 1 }, { person: { name: "Phil", id: 2 }, role: 1 }, { person: { name: "Steve", id: 1 }, role: 3 }, { person: { name: "Phil", id: 2 }, role: 6 }],
    grouped = data.reduce((r, o) => {
        var index = r.findIndex(({ person: { id } }) => id === o.person.id);
        if (index === -1) {
            r.push(o);
            return r;
        }
        if (r[index].role < o.role) {
            r[index] = o;
        }
        return r;    
    }, []);

console.log(grouped);

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answered Dec 24, 2018 at 15:30

Nina Scholz

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Comments

Ori Drori · Accepted Answer · 2018-12-24 15:44:19Z

1

Group the items by person.id with Array.reduce(), but for each id store only the object with the highest role. Convert back to array using Object.values():

const data = [{ person: { name: "Steve", id: 1 }, role: 1 }, { person: { name: "Phil", id: 2 }, role: 1 }, { person: { name: "Steve", id: 1 }, role: 3 }, { person: { name: "Phil", id: 2 }, role: 6 }];

const result = Object.values(data.reduce((r, o) => {
  const id = o.person.id;
  
  if(!r[id] || r[id].role < o.role) r[id] = o;
  
  return r;
}, []));

console.log(result);

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answered Dec 24, 2018 at 15:44

Ori Drori

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Comments

Tom O. · Accepted Answer · 2018-12-24 17:07:01Z

You could use Array.prototype.reduce and build out an object literal like below. Use the person.name property value as the object key and then just update the role value if you find a higher value:

var people = [{
  person: {
    name: "Steve",
    id: 1
  },
  role: 1
}, {
  person: {
    name: "Phil",
    id: 2
  },
  role: 1
}, {
  person: {
    name: "Steve",
    id: 1
  },
  role: 3
}, {
  person: {
    name: "Phil",
    id: 2
  },
  role: 6
}];

var highRoleByPerson = people.reduce((accum, el) => {
  if (accum[el.person.name]) {
    if (el.role > accum[el.person.name].role) {
      accum[el.person.name].role = el.role;
    }
  } else {
    accum[el.person.name] = {
      person: {
        name: el.person.name,
        id: el.person.id
      },
      role: 0
    };
  }
  return accum;
}, {});

console.log(highRoleByPerson);

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