c# print qr code First steps with LINQ to Objects: Querying collections in memory in Visual C#

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First steps with LINQ to Objects: Querying collections in memory
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That s all for the required software. Let s now review the programming languages we ll use in this book. Language considerations In this book, we assume you know the syntax of the C# programming language and occasionally a bit of VB.NET. For the sake of simplicity, we ll be light on the explanations while we introduce our first few code samples. Don t worry: In chapters 2 and 3, we ll take the time to present in detail the syntax evolutions provided by C# 2.0, C# 3.0, VB.NET 9.0, and LINQ. You will then be able to fully understand LINQ queries.
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NOTE
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Most of the examples contained in this book are in C#, but they can easily be ported to VB.NET, because the syntax is similar between the two languages. Code examples are in VB.NET when we examine the features specific to this language or simply when it makes sense. All the code samples are available both in C# and VB.NET as a companion source code download, so you can find them in your language of choice.
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All right, enough preliminaries! Let s dive into a simple example that will show you how to query a collection in memory using LINQ to Objects. Follow the guide, and be receptive to the magic of all these new features you ll be using soon in your own applications.
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Hello LINQ to Objects
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You may have had little contact with these new concepts and syntactic constructs. Fear not! Our ultimate goal is for you to master these technologies, but don t force yourself to understand everything at once. We ll take the time we need to come back to every detail of LINQ and the new language extensions as we progress through the book. Listing 1.6 shows our first LINQ example in C#.
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Listing 1.6 Hello LINQ in C# (HelloLinq.csproj)
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using System; using System.Linq; static class HelloWorld { static void Main() {
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Introducing LINQ
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string[] words = { "hello", "wonderful", "linq", "beautiful", "world" }; var shortWords = from word in words where word.Length <= 5 select word;
Get only short words
foreach (var word in shortWords) Console.WriteLine(word); } }
Print each word out
Listing 1.7 shows the same example in VB.NET.
Listing 1.7 Hello LINQ in VB.NET (HelloLinq.vbproj)
Module HelloWorld Sub Main() Dim words As String() = _ { "hello", "wonderful", "linq", "beautiful", "world" } Dim shortWords = _ From word In words _ Where word.Length <= 5 _ Select word For Each word In shortWords Console.WriteLine(word) Next End Sub End Module
Get only short words
Print each word out
NOTE
Most of the code examples contained in this book can be copied and pasted without modification into a console application for testing.
If you were to compile and run these codes, here is the output you d see:
hello linq world
As is evident from the results, we have filtered a list of words to select only the ones whose length is less than or equal to five characters. We could argue that the same result could be achieved without LINQ using the code in listing 1.8.
First steps with LINQ to Objects: Querying collections in memory
Listing 1.8
Old-school version of Hello LINQ (OldSchoolHello.csproj)
using System; static class HelloWorld { static void Main() { string[] words = new string[] { "hello", "wonderful", "linq", "beautiful", "world" }; foreach (string word in words) { if (word.Length <= 5) Console.WriteLine(word); } } }
Notice how this old-fashioned code is much shorter than the LINQ version and very easy to read. Well, don t give up yet. There is much more to LINQ than what we show in this first simple program! If you read on, we will help you discover all the power of LINQ to Objects, LINQ to SQL, and LINQ to XML. To give you some motivation to pursue reading, let s try to improve our simple example with grouping and sorting. This should give you an idea of why LINQ is useful and powerful. In order to get this result
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