How to get users id after filter and map

Question

I am trying to create an Object with the name and user id for each service, I want the object to look like this:

const object = {
    name: Netflix, user: (user id who pays max price for this provider)
    name: Comcast, user: (same)
    name: Verizon, user: (same)
}

I have tried changing the object property in the map return but it's not working, also I already have the object half done I mean with the names of the providers now I need the other key,value pair

const services = [
     { userid: 1, providerId: 1, amount: 250000 },
     { userid: 4, providerId: 3, amount: 280900 },
     { userid: 6, providerId: 3, amount: 31000 },
     { userid: 2, providerId: 2, amount: 58600 },
     { userid: 3, providerId: 1, amount: 13000 },
     { userid: 5, providerId: 2, amount: 5000 },
     { userid: 3, providerId: 3, amount: 59900 },
     { userid: 6, providerId: 3, amount: 9500 }
]

const providers = [
    { id: 1, name: Netflix },
    { id: 2, name: Comcast },
    { id: 3, name: Verizon }
]

This is my function

function getUserId(providerId) {
    return services.filter(function(obj) {
        if (obj.providerId == providerId)
            return obj.providerId;
    }).map(function(obj) { return obj.amount });
}

function getMaxUserId(providerId) {
    return Math.max(...getUserId(providerId));
}

providers.forEach(prov => {
    object[prov.name] = getUserId(prov.id);
})

as you can see first I filter the entire array looking for the providers with certain providerId then I create a new array with map function filled with all the 'amounts' for that particular provider and last I search for the max amount of that array, this all works fine it return the right max amount for each provider BUT I also want to get the user id who's paying the most for each provider

actually I'm getting my object like this:

[
   {name: Netflix, user: 250000},
   {name: Comcast, user: 58600},
   {name: Verizon, user: 280900}
]

and I need this:

[
   {name: Netflix, user: 1},
   {name: Comcast, user: 2},
   {name: Verizon, user: 4}
]

Answer 1

You could also sort your services on the amount. Then you can group them by the providerId and finally map over the providers to get the output you want:

const services = [ { id: 1, providerId: 1, amount: 250000 }, { id: 4, providerId: 3, amount: 280900 }, { id: 6, providerId: 3, amount: 31000 }, { id: 2, providerId: 2, amount: 58600 }, { id: 3, providerId: 1, amount: 13000 }, { id: 5, providerId: 2, amount: 5000 }, { id: 3, providerId: 3, amount: 59900 }, { id: 6, providerId: 3, amount: 9500 } ]
const providers = [ { id: 1, name: 'Netflix' }, { id: 2, name: 'Comcast' }, { id: 3, name: 'Verizon' } ] 

let grouped = services
  .sort((a,b) => b.amount - a.amount)  // sort `desc`
  .reduce((r,c) => ((r[c.providerId] = r[c.providerId] || []).push(c), r), {})
	
let result = providers.map(p => ({name: p.name, user: grouped[p.id][0].id}))

console.log(result)

You could also skip the sort above and check the amount and based on that either push or unshift:

const services = [ { id: 1, providerId: 1, amount: 250000 }, { id: 4, providerId: 3, amount: 280900 }, { id: 6, providerId: 3, amount: 31000 }, { id: 2, providerId: 2, amount: 58600 }, { id: 3, providerId: 1, amount: 13000 }, { id: 5, providerId: 2, amount: 5000 }, { id: 3, providerId: 3, amount: 59900 }, { id: 6, providerId: 3, amount: 9500 } ]
const providers = [ { id: 1, name: 'Netflix' }, { id: 2, name: 'Comcast' }, { id: 3, name: 'Verizon' } ] 

let groupedById = services.reduce((acc, cur) => { 
  let k = cur.providerId
  acc[k] = acc[k] || []
  if(acc[k][0] && acc[k][0].amount > cur.amount) acc[k].push(cur)
  else acc[k].unshift(cur)
  return acc
}, {})

let result = providers.map(({name, id}) => ({name, user: groupedById[id][0].id}))

console.log(result)

This way you only have one Array.reduce and one Array.map which will be more performant than your original version which has forEach, filter and map.

Answer 2

And, as a third possible solution to your problem (following up on my comment), you can use something like this (you can modify the object however you deem more to your liking, but I would suggest getting rid of name and user keys altogether):

const object = {};

function getUserId(providerId) {
    return services.filter(function(obj) {
        if (obj.providerId == providerId)
            return obj.providerId;
    }).map(function(obj) { return obj });
}

function getMaxUserId(output) {
    let amm = output.map( (o) => { return o.amount; } );
    let idx = amm.indexOf(Math.max(...amm));
    return output[idx].userid;
}

providers.forEach(prov => {
    object[prov.name] = getMaxUserId(getUserId(prov.id));
})

console.log(object)

The output in your case using this solution will look like this:

Object { Netflix: 1, Comcast: 2, Verizon: 4 }

Ofc, with a small tweak you will be able to return an Array with objects as originally intended (don't forget to assign object to [] instead):

providers.forEach(prov => {
  object.push( {name:prov.name,user:getMaxUserId(getUserId(prov.id))} )
})

In the latter case the output will look like this:

Array [Object { name: "Netflix", user: 1 }, Object { name: "Comcast", user: 2 }, Object { name: "Verizon", user: 4 }]

Answer 3

Ideally we'd have argmax in JS. But for now, normal iteration looks nicer. Note the rarely-seen == because JS turns the dictionary keys into strings:

var maxes = {};
services.forEach(item => {
    if(!maxes[item.providerId] || maxes[item.providerId] < item.amount[0]) {
        maxes[item.providerId] = [item.amount, item.id];
    }
});
function providerById(id) {
    return providers.filter(p => p.id == key)[0].name;
}
console.log(Object.keys(maxes).map(key => {
    return { name: providerById(key), user: maxes[key][1] };
}));