Restriction and Projection Operators in LINQ

In this article we will learn how to use LINQ operators in our application. I would also be covering the entire range of Linq functionality in this sample code.

Before we proceed to the coding for using LINQ operators I would like to first briefly describe what is LINQ.

Defination of LINQ as given in books: Language-Integrated Query (LINQ) is a set of features introduced in Visual Studio 2008 that extends powerful query capabilities to the language syntax of C# which have many operators. We will look through the restriction and Partition operators of LINQ.

Restriction Operator of LINQ

1. Where Clause

Suppose we have a list of strings and we want to filter it by the names which starts with 'A'.
string[] names = { "Asyl", "Bail", "Manu", "Agni", "Jay" };

In fluent syntax the query will be...

IEnumerable query = names.Where (name => name.StartsWith ("A"));
foreach(var item in query)
{
  Console.WriteLine(item);
}
//Output
Asyl
Agni

In normal query syntax...

IEnumerable query = from n in names
	                    where n.StartsWith ("y")
	                    select n;
foreach(var item in query)
{
  Console.WriteLine(item);
}
//Output
Asyl
Agni

Projection Operators of LINQ

1. Select Clause

Suppose we have a list of numbers and we want to select the numbers by adding 1 to it.

var numbers = { 6, 9, 4, 3, 0, 1 };
var query = from n in numbers select n+1;
foreach(var item in query)
{
  Console.WriteLine(item);
}
//OutPut
7
10
5
4
1
2

2. Select Many Clause
Suppose we have two lists of numbers and we want to select the numbers from both the list where listA is less than listB.

var listA = { 6, 9, 4, 3, 0, 1 };
var listB = { 1, 2, 5, 8, 9, 5, 4};

var query = from a in listA
            from b in listB
            where a < b
            select new {a,b};
foreach(var item in query)
{
  Console.WriteLine(item.a + " < " + item.b);
}

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