Скачать или смотреть How to Use LINQ and Lambda Expressions to Group Data by Multiple Columns in C#

Discover how to effectively group data in C# with LINQ and lambda expressions, filtering results with `Skip` and `Take` functions.
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This video is based on the question https://stackoverflow.com/q/62862719/ asked by the user 'Steven Sann' ( https://stackoverflow.com/u/9587283/ ) and on the answer https://stackoverflow.com/a/62862755/ provided by the user 'juharr' ( https://stackoverflow.com/u/302918/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Grouping Data in C# with LINQ: A Step-by-Step Guide

When working with data in C# , especially when retrieving records from a database, you often encounter situations where you need to manipulate and group that data. One common use case is to group records by multiple columns and retrieve specific entries from these groups.

In this post, we'll discuss how to efficiently use LINQ with lambda expressions to group data by multiple columns, choose the first item within each group, and filter the results. Let's dive into the details!

The Problem

Suppose you have a dataset that resembles the following table:

[[See Video to Reveal this Text or Code Snippet]]

What We Want to Achieve

Group by C1 and C2 columns.

Get the first item from each group based on the C3 column in descending order.

Filter the results to skip the first two records and take the next four.

The expected outcome would look like this:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To achieve the desired output, we can utilize LINQ with lambda expressions. Here's a clear breakdown of the steps involved:

1. Group By Multiple Columns

To group the data by C1 and C2, use the GroupBy method. We will create an anonymous object encapsulating both C1 and C2.

2. Select the First Item

After grouping, we'll need to select the first entry of each group. The First() method will help us retrieve the first record from the grouped collections.

3. Sorting the Results

Before selecting the first item in each group, you should sort the groups based on the C3 column in descending order.

4. Skip and Take

Finally, to filter the results, we'll use the Skip and Take methods. The Skip(1) function will skip the first record, and Take(4) will retrieve the next four records.

5. The Complete Code

Here's the complete LINQ query that incorporates all the steps outlined above:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Using LINQ and lambda expressions in C# greatly simplifies the process of grouping data by multiple columns and extracting relevant information. By following the steps above, you can easily customize and adapt the methods to suit your specific data retrieval needs.

By understanding the powerful capabilities of LINQ, you can efficiently manipulate your datasets and ensure you get the exact data you need!

If you have any questions or need further clarification on the topic, feel free to leave a comment below!