比较两个数组，取出重复项

Question

I built a courses page with 3 courses, i want to build it in a way that all the courses are displayed with a buy button, the course info is collected from the database via the products collection. then i want that if the user bought the course, instead of buy, watch will be displayed.

to do that i have 2 arrays: 1) all the products 2) the products that the user bought

now i want to compare them, and delete from the first array all the products that the user already bought.

i tried checking online for methods, but i didn't understand them at all.

Here is the function to get the arrays:

const productRef = await db.collection("products").get();

  const products = await productRef.docs.map(doc => {
    return {
      id: doc.id,
      name: doc.data().name,
      price: doc.data().price
    };
  });
  console.log(products);
//[ { id: 'course1', name: 'Course 1', price: 25 },
  { id: 'course2', name: 'Course 2', price: 10 },
  { id: 'course3', name: 'Course 3', price: 30 } ]


  if (user) {
    const claims = res.locals.decodedClaims;
    const uid = claims.uid;
    const email = claims.email;

    const userProductsRef = await db
      .collection("users")
      .doc(uid)
      .collection("courses")
      .get();

        if (userProductsRef.docs.length > 0) {
      const userProducts = userProductsRef.docs.map(doc => {
        return { id: doc.id, name: doc.data().name };
      });
      console.log(userProducts);//[ { id: 'course1', name: 'Course 1' } ]

     ///COMPARE HERE the two arrays
    }
  }

now i want to compare products with userProducts by the id.

so expected result at the end should be something like:

products= [ 
  { id: 'course2', name: 'Course 2', price: 10 },
  { id: 'course3', name: 'Course 3', price: 30 } ];

userProducts=  [ { id: 'course1', name: 'Course 1' } ]

Thank You!

Answer 1

You can filter the products array by checking to see if each product id is in the userProducts array:

const filteredProducts = products
  .filter(prod => !userProducts.find(userProd => userProd.id === prod.id))

console.log(filteredProducts)

// [ 
//   { id: 'course2', name: 'Course 2', price: 10 },
//   { id: 'course3', name: 'Course 3', price: 30 }
// ]

I hope this is what you were looking for.

Answer 2

You could use a combination of .filter() and .find() to achieve what you want:

 const products = [ { id: 'course1', name: 'Course 1', price: 25 }, { id: 'course2', name: 'Course 2', price: 10 }, { id: 'course3', name: 'Course 3', price: 30 }, ]; const userProducts = [ { id: 'course1', name: 'Course 1' } ]; const result = products.filter(product => { return !userProducts.find(o => o.id === product.id); }); console.log(result);