How to define Typescript Map of key value pair. where key is a number and value is an array of objects

Question

In my angular2 app i want to create a map which takes a number as key and returns an array of objects. I am currently implementing in following way but no luck. How should i implement it or should i use some other data structure for this purpose? I want to use map because maybe its fast?

Declaration

 private myarray : [{productId : number , price : number , discount : number}];

priceListMap : Map<number, [{productId : number , price : number , discount : number}]> 
= new Map<number, [{productId : number , price : number , discount : number}]>();

Usage

this.myarray.push({productId : 1 , price : 100 , discount : 10});
this.myarray.push({productId : 2 , price : 200 , discount : 20});
this.myarray.push({productId : 3 , price : 300 , discount : 30});
this.priceListMap.set(1 , this.myarray);
this.myarray = null;

this.myarray.push({productId : 1 , price : 400 , discount : 10});
this.myarray.push({productId : 2 , price : 500 , discount : 20});
this.myarray.push({productId : 3 , price : 600 , discount : 30});
this.priceListMap.set(2 , this.myarray);
this.myarray = null;

this.myarray.push({productId : 1 , price : 700 , discount : 10});
this.myarray.push({productId : 2 , price : 800 , discount : 20});
this.myarray.push({productId : 3 , price : 900 , discount : 30});
this.priceListMap.set(3 , this.myarray);
this.myarray = null;

I want to get an array of 3 objects if i use this.priceList.get(1);

Nitzan Tomer · Accepted Answer · 2017-07-28T12:59:12.377

101

First thing, define a type or interface for your object, it will make things much more readable:

type Product = { productId: number; price: number; discount: number };

You used a tuple of size one instead of array, it should look like this:

let myarray: Product[];
let priceListMap : Map<number, Product[]> = new Map<number, Product[]>();

So now this works fine:

myarray.push({productId : 1 , price : 100 , discount : 10});
myarray.push({productId : 2 , price : 200 , discount : 20});
myarray.push({productId : 3 , price : 300 , discount : 30});
priceListMap.set(1 , this.myarray);
myarray = null;

(code in playground)

edited Jul 28 '17 at 12:59

answered Dec 05 '16 at 14:32

Nitzan Tomer

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In your playground link there is an error in console Uncaught TypeError: Cannot read property 'push' of undefined(…) I implemented it using an interface and i got the same error. – usmanwalana Dec 05 '16 at 15:08
1

That's because I just copied your code, and in your code you are setting `myarray` to null and then try to push to it. So either don't set it to null, or just reassign a new array later – Nitzan Tomer Dec 05 '16 at 15:14
I am getting error on type keyword, using typescript 2.1.0 – d-man Jun 12 '17 at 15:05
@Faisalkhan That shouldn't happen. Type aliases were added in [typescript 1.4](https://github.com/Microsoft/TypeScript/wiki/What's-new-in-TypeScript#type-aliases). What's the error you're getting? – Nitzan Tomer Jun 12 '17 at 15:11

score 11 · Answer 2 · edited Jun 24 '21 at 16:05

11

The most simple way is to use Record type Record<number, productDetails>

interface productDetails {
   productId : number , 
   price : number , 
   discount : number
};

const myVar : Record<number, productDetails> = {
   1: {
       productId : number , 
       price : number , 
       discount : number
   }
}

edited Jun 24 '21 at 16:05

Yves M.

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answered Jun 30 '20 at 04:56

aWebDeveloper

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score 7 · Answer 3 · edited Apr 21 '22 at 23:08

7

you can also skip creating dictionary altogether. i used below approach to same problem .

     mappedItems: {};
     items.forEach(item => {     
            if (!mappedItems[item.key]) {
              mappedItems[item.key] = [];
            }
            mappedItems[item.key].push({productId : item.productId , price : item.price , discount : item.discount}));
        });

edited Apr 21 '22 at 23:08

Ryan M

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answered Apr 20 '20 at 18:56

kumar chandraketu

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How to define Typescript Map of key value pair. where key is a number and value is an array of objects

3 Answers3

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