How to groupBy a typescript array with a Key of an object inside that array?

Question

I have an array products that needs to be grouped by Product._shop_id .

 export class Product { _id: string; _shop_id: string; } export class Variant { variant_id: string; } export interface ShoppingCart { Variant: Variant; Product: Product; quantity: number; totalPrice: number; } export class CartComponent implements OnInit { products: ShoppingCart[] = []; ngOnInit(){ this.products = [ {Variant: {variant_id: '1'}, Product: {_id: '1', _shop_id:'1'}, quantity: 5, totalPrice: 600}, {Variant: {variant_id: '2'}, Product: {_id: '2', _shop_id:'2'}, quantity: 4, totalPrice: 500}, {Variant: {variant_id: '5'}, Product: {_id: '3', _shop_id:'2'}, quantity: 3, totalPrice: 400} ] } someMethod(){ const productsByShop = this.utils.groupBy(this.products, key); } } 

Here is the method to achieve this. But I need the Object Key to make it work.

 export class Utils { constructor() { } groupBy(list, key) { const map = new Map(); list.forEach((item) => { const collection = map.get(key); if (!collection) { map.set(key, [item]); } else { collection.push(item); } }); return Array.from(map)[0][1]; } } 

I'm trying to get different arrays grouped by _shop_id from products array. Like this:

array1: [ {Variant: {variant_id: '1'}, Product: {_id: '1', _shop_id:'1'}, quantity: 5, totalPrice: 600} ]`

array2: [ {Variant: {variant_id: '2'}, Product: {_id: '2', _shop_id:'2'}, quantity: 4, totalPrice: 500},
          {Variant: {variant_id: '5'}, Product: {_id: '3', _shop_id:'2'}, quantity: 3, totalPrice: 400} ]`

Answer 1

Since your _shop_id belongs to a nested object, you're probably best off passing a lambda to extract it:

someMethod(){
  const productsByShop = this.utils.groupBy(this.products,
    (product) => product.Product._shop_id);
}
// ...
export class Utils {
    constructor() { }

    groupBy<T, K>(list: T[], getKey: (item: T) => K) {
        const map = new Map<K, T[]>();
        list.forEach((item) => {
            const key = getKey(item);
            const collection = map.get(key);
            if (!collection) {
                map.set(key, [item]);
            } else {
                collection.push(item);
            }
        });
        return Array.from(map.values());
    }
}