Lesson 3
Introduction to Data Projection Techniques in C#
Introduction to Data Projection Techniques

Welcome! Today, we'll delve into Data Projection Techniques in C#! Data projection is akin to using a special light to make diamonds shine brighter amidst other gems, aiding their identification.

This lesson will illuminate the concept of data projection, its implementation using C#’s LINQ Select method, and how to integrate it with filtering. Let's forge ahead!

Implementing Data Projection in C#

Data projection involves applying a function to a data stream's elements, resulting in a reshaped view. A common instance of data projection is selecting specific fields from datasets.

Data projection in C# employs the Select method from LINQ. You can define a reusable function using Func<int, int> to calculate each number's square, or directly embed the logic within Select for a single use. Here's an illustration using Func:

C#
1using System;
2using System.Collections.Generic;
3using System.Linq;
4
5class Program
6{
7    static void Main()
8    {
9        List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };  // our data stream
10
11        Func<int, int> square = n => n * n;  // function to get a number's square
12
13        // Select applies the square function to each number in the list
14        List<int> squaredNumbers = numbers.Select(square).ToList();
15
16        Console.WriteLine(string.Join(", ", squaredNumbers));  // prints: 1, 4, 9, 16, 25
17    }
18}

Use Func for reusability in other code parts, or embed the logic directly inside Select if it’s a one-time operation.

Data Projection in C#: Advanced Topics

For complex operations on data streams, C# employs lambda expressions (anonymous functions). Let's convert a list of sentences to lowercase:

C#
1using System;
2using System.Collections.Generic;
3using System.Linq;
4
5class Program
6{
7    static void Main()
8    {
9        List<string> sentences = new List<string> { "HELLO WORLD", "C# IS FUN", "I LIKE PROGRAMMING" };  // our data stream
10
11        // Select applies the lambda function to each sentence in the list
12        List<string> lowerSentences = sentences.Select(sentence => sentence.ToLower()).ToList();
13
14        Console.WriteLine(string.Join(", ", lowerSentences));  // prints: hello world, c# is fun, i like programming
15    }
16}
Combining Projection and Filtering

C# seamlessly integrates projection and filtering. Now, let's lowercase sentences containing "C#" while dismissing others:

C#
1using System;
2using System.Collections.Generic;
3using System.Linq;
4
5class Program
6{
7    static void Main()
8    {
9        List<string> sentences = new List<string> { "HELLO WORLD", "C# IS FUN", "I LIKE PROGRAMMING" };  // our data stream
10
11        // Where selects sentences containing 'C#'
12        List<string> filteredSentences = sentences.Where(sentence => sentence.Contains("C#")).ToList();
13
14        // Select applies the lambda function to each filtered sentence, converting it to lowercase
15        List<string> lowerFilteredSentences = filteredSentences.Select(sentence => sentence.ToLower()).ToList();
16
17        Console.WriteLine(string.Join(", ", lowerFilteredSentences));  // prints: c# is fun
18    }
19}
Integration: Creating a Data Projection Class

By creating a DataProjector class, we'll encapsulate our projections for reusable, cleaner code:

C#
1using System;
2using System.Collections.Generic;
3using System.Linq;
4
5class DataProjector<T>
6{
7    private List<T> data;
8
9    public DataProjector(List<T> data)
10    {
11        this.data = data;
12    }
13
14    public List<TResult> Project<TResult>(Func<T, TResult> projectFunc)
15    {
16        return this.data.Select(projectFunc).ToList();
17    }
18
19    public List<TResult> FilterAndProject<TResult>(Func<T, bool> filterFunc, Func<T, TResult> projectFunc)
20    {
21        List<T> filteredData = this.data.Where(filterFunc).ToList();
22        return new DataProjector<T>(filteredData).Project(projectFunc);
23    }
24}
25
26class Program
27{
28    static void Main()
29    {
30        List<string> sentences = new List<string> { "HELLO WORLD", "C# IS FUN", "I LIKE PROGRAMMING" };  // our data stream
31
32        // Creating a DataProjector object with our sentences
33        DataProjector<string> projector = new DataProjector<string>(sentences);
34
35        // Applying FilterAndProject to filter sentences containing 'C#' and converting them to lowercase
36        List<string> lowerFilteredSentencesList = projector.FilterAndProject(
37            sentence => sentence.Contains("C#"),
38            sentence => sentence.ToLower()
39        );
40
41        Console.WriteLine(string.Join(", ", lowerFilteredSentencesList));  // prints: c# is fun
42    }
43}
Summary

Awesome! You've conquered Data Projection Techniques in C#! You've understood data projection, used Select, and integrated projection with filtering.

Remember our treasure box! This knowledge is your treasure box key, unlocking data manipulation aspects like raw data cleaning or web development data transformations. Now, revisit these concepts with practice exercises for mastery. Happy coding!

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