How to filter an array with another array in React Native?

Question

So I am basically trying to say "give me all added items that were not actually added to the cart" with my filter function below. If any of the addedItems product ids cannot be found in the cartItems ids then it should return those items. But instead unaddedCartItems is an empty array when I know there are addedItems ids that are not the same as any of the cartItems ids. Do anyone know how to achieve this?

const unaddedCartItems = addedItems.filter((addedItem) => {
    cartItems.forEach((cartItem) => {
        return cartItem.id !== addedItem.productId;
    });
});

Chase DeAnda · Accepted Answer · 2018-03-27 17:52:17Z

3

It's because your return is nested under forEach and you aren't returning that value in your filter. Instead, use find:

const unaddedCartItems = addedItems.filter( addedItem => {
    return !cartItems.find( cartItem => cartItem.id === addedItem.productId );
});

find loops through an array until it finds a matching item. This means that if it finds the id in cartItems, it will immediately stop the loop and return the item.

edited Mar 27, 2018 at 17:52

answered Mar 27, 2018 at 17:41

Chase DeAnda

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2 Comments

Ele Over a year ago

Function find to accomplish that requirement? What about the function some?

Ele Over a year ago

Although will work, the best approach is using the function some.

emjrose · Accepted Answer · 2018-03-27 17:43:07Z

2

Would using some work here?

const unaddedCartItems = addedItems.filter((addedItem) => 
    !cartItems.some(cartItem => cartItem.id === addedItem.productId);

edited Mar 27, 2018 at 17:43

answered Mar 27, 2018 at 17:41

emjrose

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6 Comments

Chase DeAnda Over a year ago

You still need to return the result from .some

Chase DeAnda Over a year ago

This is also less performant than find when you have a lot of items in your cart. If the item doesn't exist in the cart, this code will loop through every cartItem instead of stopping once it finds a match.

Ruan Mendes Over a year ago

@ChaseDeAnda That's incorrect, Array#some tells you whether a single element matches it, so it will also stop after it finds it, and is the better one to use because in find, you are wasting its return value since we only need a boolean.

Chase DeAnda Over a year ago

Right, they both work the same, but how they are using it here is missing out on the performance of using .some or .find.

Ele Over a year ago

@ChaseDeAnda the way was implemented that arrow function doesn't need a return statement.

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Ashraf Samir · Accepted Answer · 2018-03-27 17:47:21Z

0

because your return is nested under forEach and you aren't returning that value in your filter

answered Mar 27, 2018 at 17:47

Ashraf Samir

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1 Comment

Chase DeAnda Over a year ago

So how should OP fix it? They want to know a solution to their problem, not just why it's not working.

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