分组列表并转换为 IEnumerable

Question

I have the following List:

var products = new List<(int ProductId, int Quantity)>
{
    (10125237,2),
    (7775711,1),    
};

And I am grouping the list as follows:

var groupedCustomerList = products
    .GroupBy(u => u.ProductId)
    .Select(grp => grp.AsEnumerable());

I then pass the grouped list to the following Method:

public Builder Products(IEnumerable<(int ProductId, int Quantity)> products)
{
    this.products.AddRange(products);
    return this;
}

But when I compile, I get the following error:

cannot convert from 'System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable<(int VariantId, int Quantity)>>' to 'System.Collections.Generic.IEnumerable<(int variantId, int quantity)>'

Am I missing something since I have already converted groupedCustomerList to an IEnumerable ?

Answer 1

You probably want the total quantity by product Id:

var groupedProductList = products
    .GroupBy(u => u.ProductId)
    .Select(g => (ProductId: g.Key, Quantity: g.Sum(p => p.Quantity)));

This is achieved by creating a tuple in the Select-clause. The product Id is the key of the group (since we grouped by this Id). Instead of retrieving a enumeration of products in the group, we sum the quantities of these products.

Note that your original query yields a IEnumerable<IEnumerable<(int, int)>> , ie, nested enumerations.

This solution returns a simple enumeration: IEnumerable<(int ProductId, int Quantity)> compatible with your builder method.

Answer 2

U can directly pass the list to the function as List already inherits IEnumerable interface.