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} ]`

Matt McCutchen · Accepted Answer · 2018-08-15 03:28:53Z

12

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());
    }
}

answered Aug 15, 2018 at 3:28

Matt McCutchen

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