How to Correctly Use LINQ GroupBy, Sum, and Count to Aggregate Product Data?

LINQ: GroupBy, Sum and Count

The goal of this code is to group a collection of products by product code and return an object containing the product name, the product quantity for each code, and the total price of each product.

The sample data contains three products:

<code>{"p1", 6.5, "Product1"}, {"p1", 6.5, "Product1"}, {"p2", 12, "Product2"}</code>

The expected results are as follows:

<code>Product1: count 2   - Price:13 (2x6.5)
Product2: count 1   - Price:12 (1x12)</code>

However, the count value generated by the code is incorrect, always showing 1 for each product.

The problem is that the SelectMany() method is used incorrectly. The code should use the Select() method, which simplifies expressions:

<code>List<ResultLine> result = Lines
    .GroupBy(l => l.ProductCode)
    .Select(cl => new ResultLine
            {
                ProductName = cl.First().Name,
                Quantity = cl.Count().ToString(),
                Price = cl.Sum(c => c.Price).ToString(),
            }).ToList();</code>

This modification corrects the problem and produces the desired count value:

<code>Product1: count 2   - Price:13 (2x6.5)
Product2: count 1   - Price:12 (1x12)</code>

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