angulartypescriptecmascript-6lodash

Is it possible to "filter" a Map by value in Typescript?

I am looking for a way to filter a map by value instead of key. I have a data set that is modeled as follows in my Angular application:

{
  "85d55e6b-f4bf-47bb-a988-78fdb9650ef0": {
    is_deleted: false,
    public_email: "007@example.org",
    id: "85d55e6b-f4bf-47bb-a988-78fdb9650ef0",
    modified_at: "2017-09-26T15:35:06.853492Z",
    social_url: "https://facebook.com/jamesbond007",
    event_id: "213b01de-da9e-4d19-8e9c-c0dae63e019c",
    visitor_id: "c3c232ff-1381-4776-a7f2-46c177ecde1c",
  },
}

The keys on these entries are the same as the id field on the entries values.

Given several of these entries, I would like to filter and return a new Map() that contains only those entries with a given event_id. Were this an array I would just do the following:

function example(eventId: string): Event[] {
  return array.filter((item: Event) => item.event_id === eventId);
}

Essentially, I am attempting to replicate the functionality of Array.prototype.map() - just on a Map instead of an Array.

I am willing to use Lodash if it will help achieve this in a more succinct way as it is already available in my project.

Solution

  • If a key matters, and the result needs to be a new Map, it is:

    new Map(
  [...map.entries()]
  .filter(([key, item]) => item.event_id === eventId)
)

    A similar approach has been already suggested in other answers and listed for completeness.

    If a key doesn't matter, a map can be converted to an array:

    [...map.values()]
.filter((item: Event) => item.event_id === eventId);

    Array.from(map.values()) should be used instead of [...map.values()], etc for TypeScript without downlevelIteration option.