CODEWITHSUNDEEP
jsonangularrxjs
Jérémy Halin
Jérémy Halin

Reputation: 563

How to do a groupBy with RxJS and get results in specific array?

I have an object with these properties :

{
    title: 'Test',
    places: [
      {
        id: 1,
        longitude: 48.8469511,
        latitute: 2.3077989,
        address: 'Pont de Bir-Hakeim',
        city: {name: 'Paris', id: 1}
      },
      {
        id: 2,
        longitude: 48.855225,
        latitute: 2.288048,
        address: 'Palais-Musée Galliera, 10 avenue Pierre-1er-de-Serbie',
        city: {name: 'Paris', id: 1}
      },
      {
        id: 3,
        longitude: 50.8283315,
        latitute: -115.2608429,
        address: 'Fortress Moutain',
        city: {name: 'Calgary', id: 2}
      }
    ]
}

Here is the result I want :

[
  {
    id: 1,
    name: 'Paris'
  },
  {
    id: 2,
    name: 'Calgary'
  },
]

How can I achieve that by using groupBy map reduce ? Here is what I tried :

   return from(movie.places).pipe(
      groupBy(place => place.city.name),
      mergeMap(place => place.pipe(map(obj => obj.city.name))),
      toArray()
   );

Which produce :

['Paris', 'Paris', 'Calgary']

It's not very clear in my head on how to use groupBy, map, mergeMap, toArray together... Thanks for the help!

Upvotes: 1

Views: 995

Answers (2)

SeleM
SeleM

Reputation: 9638

In one line, I think, and just using toArray, map, distinct operators you can do: 

return from(movie.places).pipe(map(place => place.city), distinct(entry => entry.id),toArray());

Demo

Upvotes: 0

Yanis-git
Yanis-git

Reputation: 7875

you can do something like this :

source$.pipe(
  map(state => state.places), // transform your source object to list of places.
  // Transform your list of place by list of city, then reduce it for unduplicate it.
  map(state => state.map(e => e.city).reduce( ( acc, cur ) => [
    ...acc.filter( ( obj ) => obj.id !== cur.id ), cur
  ], [] ))
).subscribe(console.log);

i have split in two different map to keep clear my code, you can easily merge it to single map if you prefer.

this code is also not safe for very large collection of data, prefer normalizr approch if you want to efficiently deal with larg data.

live code

source for uniq array of object base from id

Upvotes: 1

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