如果另一个数组包含对象，如何减少对象数组？

Question

I have two arrays of objects, one contains Shops with it's id , name etc. and another with Products each product has shop_id property in it and i have a filter function which by passing Shop id returns all Products of that shop. The issue is that there could be Shops without items and i would remove that Shops from the array.

So i was going to use .reduce to do it with a .filter on Products Array but i can't get on how i can return the array with only Shops that has some items

i was trying to do something like this

 var shops = [ { id: 123, desc: 'Pippo' }, { id: 124, desc: 'Pluto' }, { id: 125, desc: 'Gianni' } ] const products = [ { id: 1, desc: 'Car', shop: 123 }, { id: 2, desc: 'Jet', shop: 123 }, { id: 3, desc: 'Pizza', shop: 124 } ] shops = shops.reduce((a,b) => { products.filter((item) => item.menu === b.id).length ? b : a }) console.log(shops) // shouldn't return shop 125 as no items in products for its id.

Answer 1

I think you could accomplish this with array.filter and array.some :

 const shops = [{ id: 'shop1' },{ id: 'shop2' },{ id: 'shop3'},] const products = [ { pid: 'product1', shop: 'shop1'}, { pid: 'product3', shop: 'shop3'}, ]; const shopsWithProducts = shops.filter(shop => products.some(p => p.shop === shop.id)); console.log(shopsWithProducts);

Answer 2

You could group the products based on their shop property, creating a lookup object in the process. This method should be faster when working with large amounts of shops and products, since you only iterate products once.

 var shops = [ { id: 123, desc: 'Pippo' }, { id: 124, desc: 'Pluto' }, { id: 125, desc: 'Gianni' } ]; const products = [ { id: 1, desc: 'Car', shop: 123 }, { id: 2, desc: 'Jet', shop: 123 }, { id: 3, desc: 'Pizza', shop: 124 } ]; const productsByShop = groupBy(products, product => product.shop); shops = shops.filter(shop => productsByShop.get(shop.id)); console.log(shops) // shouldn't return shop 125 as no items in products for its id. // helper function groupBy(iterable, fn) { const groups = new Map(); for (const item of iterable) { const key = fn(item); if (!groups.has(key)) groups.set(key, []); groups.get(key).push(item); } return groups; }