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

问题

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.

回答1:

It is

Array.from(map.values()).filter((item: Event) => item.event_id === eventId);

Or for TypeScript downlevelIteration option,

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

回答2:

Using lodash:

_.pickBy(thing, function(value, key) {
  return value.event_id == eventId;
});

回答3:

First you need to flatten the map, Then extract the contents to an Events object

let dataSet = {
     "entry1" : {  id: "85d55e6b-f4bf-47b0" },
     "entry2" : {  visitor_id: "6665b-7555bf-978b0" } 
}

 let flattenedMap = {};
    Object.entries(dataSet).forEach(
           ([key,value]) => Object.assign(flattenedMap, value)
     );
  

console.log("The flattened Map")
console.log(flattenedMap)

let events = [];
Object.entries(flattenedMap).forEach(
    ([key, value]) => events.push({"event_id" : value})
);

console.log("The events");
console.log(events);

来源：https://stackoverflow.com/questions/46605403/is-it-possible-to-filter-a-map-by-value-in-typescript

标签

angular

typescript

ecmascript-6

lodash