Home Backend Development C++ How to Correctly Group, Sum, and Count Products in LINQ with GroupBy?

How to Correctly Group, Sum, and Count Products in LINQ with GroupBy?

Jan 24, 2025 pm 05:01 PM

How to Correctly Group, Sum, and Count Products in LINQ with GroupBy?

Group, sum and count products using LINQ: GroupBy method

Problem Description

We have a collection of products that need to be grouped by product code. The goal is to create an object that contains the product name, product quantity, and total price for each product code.

Code snippet (error example)

The initial code uses GroupBy to group by product code and then calculate the sum and count for each group.

List<resultline> result = Lines
    .GroupBy(l => l.ProductCode)
    .SelectMany(cl => cl.Select(
        csLine => new ResultLine
        {
            ProductName = csLine.Name,
            Quantity = cl.Count().ToString(),
            Price = cl.Sum(c => c.Price).ToString(),
        })).ToList<resultline>();
Copy after login

The problem

While this code calculates the sum correctly, the count for all products always shows 1.

Example data

List<cartline> Lines = new List<cartline>();
Lines.Add(new CartLine() { ProductCode = "p1", Price = 6.5M, Name = "Product1" });
Lines.Add(new CartLine() { ProductCode = "p1", Price = 6.5M, Name = "Product1" });
Lines.Add(new CartLine() { ProductCode = "p2", Price = 12M, Name = "Product2" });
Copy after login

Expected results

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

Solution

The problem is using SelectMany to check every item in every group. The correct approach is:

List&lt;resultline&gt; result = Lines
    .GroupBy(l =&gt; l.ProductCode)
    .Select(cl =&gt; new ResultLine
    {
        ProductName = cl.First().Name,
        Quantity = cl.Count().ToString(),
        Price = cl.Sum(c =&gt; c.Price).ToString(),
    }).ToList();
Copy after login

Assuming products with the same code have the same name, we can use First() to get the product name. SelectMany flattens the result set, causing counting errors, while Select directly operates on the grouped results.

This revised answer maintains the image and provides a more accurate and concise explanation of the LINQ problem and solution. The wording is also adjusted for improved clarity and flow.

The above is the detailed content of How to Correctly Group, Sum, and Count Products in LINQ with GroupBy?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot Article Tags

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

What are the types of values ​​returned by c language functions? What determines the return value? What are the types of values ​​returned by c language functions? What determines the return value? Mar 03, 2025 pm 05:52 PM

What are the types of values ​​returned by c language functions? What determines the return value?

What are the definitions and calling rules of c language functions and what are the What are the definitions and calling rules of c language functions and what are the Mar 03, 2025 pm 05:53 PM

What are the definitions and calling rules of c language functions and what are the

Gulc: C library built from scratch Gulc: C library built from scratch Mar 03, 2025 pm 05:46 PM

Gulc: C library built from scratch

C language function format letter case conversion steps C language function format letter case conversion steps Mar 03, 2025 pm 05:53 PM

C language function format letter case conversion steps

Where is the return value of the c language function stored in memory? Where is the return value of the c language function stored in memory? Mar 03, 2025 pm 05:51 PM

Where is the return value of the c language function stored in memory?

distinct usage and phrase sharing distinct usage and phrase sharing Mar 03, 2025 pm 05:51 PM

distinct usage and phrase sharing

How do I use algorithms from the STL (sort, find, transform, etc.) efficiently? How do I use algorithms from the STL (sort, find, transform, etc.) efficiently? Mar 12, 2025 pm 04:52 PM

How do I use algorithms from the STL (sort, find, transform, etc.) efficiently?

How does the C   Standard Template Library (STL) work? How does the C Standard Template Library (STL) work? Mar 12, 2025 pm 04:50 PM

How does the C Standard Template Library (STL) work?

See all articles