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

user_2120093 0
Viewed 54270

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.

lodash angular typescript ecmascript-6
5 Answers

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);
user_37315010

Here's a short syntax that keeps keys and values together:

const dict = new Map([["Z", 1324], ["A", 1], ["B", 2], ["C", 3], ["D", -12345]])

const filtered = [...dict.entries()].filter( it => it[1] < 10 ) 

// >  [ [ 'A', 1 ], [ 'B', 2 ], [ 'C', 3 ], [ 'D', -12345 ] ]
user_21924830

This one uses Object.entries to convert the map to an array, and Object.fromEntries to convert back to map.

let qs = {a:'A 1',b:null,c:'C 3'};
let qsfiltered = Object.fromEntries(
    Object.entries(qs).filter(([k,v]) => v !== null)
);

console.log(JSON.stringify(qsfiltered));
user_3114820 
export class MapUtils {
  static filter<TKey, TValue>(map: Map<TKey, TValue>, filterFunction: (key: TKey, value: TValue) => boolean): Map<TKey, TValue> {
    const filteredMap: Map<TKey, TValue> = new Map<TKey, TValue>();
    
    map.forEach((value, key) => {
      if (filterFunction(key, value)) {
        filteredMap.set(key, value);
      }
    });
    
    return filteredMap;
  }
}

usage:

 const filteredMap = MapUtils.filter(map, (key, value) => value > 0)
user_46955190

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);

user_33350540
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