how to merge more than one list into only one list? dart

Question

i have a

class shop {
int id;
String name;
List<Product> products;
}

class Product {
int id;
String productName;
}

where each shop has his own products , how to merge all shops products in one list how to create a List of all products

Solution 1

You can merge lists using + or the spread operator

Using the Addition Operator:

List<shop> shops = [shop1, shop2];
List<Product> products = shop1.products + shop2.products;

Using Spread Operator:

List<Product> products = [...shop1.products, ...shop2.products];

Edit

You would need to do it like this:

List<shop> shops = [shop1, shop2,...];
List<Product> mergedProducts = []
for(int i = 0; i < shops.length; i++){
    mergedProducts = mergedProducts + shops[i].products;
}

Solution 2

You can simply merge Lists with + operator:

List<Product> list1 = ...;
List<Product> list2 = ...;
List<Product> list3 = ...;

List<Product> mergedList = list1 + list2 + list3;

Also, Dart 2.3 and higher supports spread operator, which can be used as follows:

List<Product> mergedList2 = [...list1, ...list2, ...list3];

For dynamic number of shops you can use basic forEach:

List<Shop> shops = ...;

List<Product> mergedList = List();

shops.forEach((shop) => mergedList.addAll(shop.products));

Comments

[pskink]

what is your input data? how can you assign a product to shop? i am assuming that Product.id is "product ID" and not "ID of shop that product belongs to"

[ialyzaafan]

okay but i have a dynamic number of shops not constant is there a way to loop on List<Shop> shops and create the all products List ?

[ialyzaafan]

okay but i have a dynamic number of shops not constant is there a way to loop on List<Shop> shops and create the all products List ?

[asterisk12]

If my answer helped, please mark it correct so that other people who might have the same problem can see it!

[ialyzaafan]

The expression here has a type of 'void', and therefore can't be used. Try checking to see if you're using the correct API; there might be a function or call that returns void you didn't expect. Also check type parameters and variables which might also be void

[konstantin_doncov]

@ialyzaafan did this help you?

[asterisk12]

To help you further, I would have to see your code!