How to use Projection Operatiors in LINQ?

we have many projection operators in linq like: Select(),where()....are Extension methods takes delegates as

input parameters

    var numbers = new[] { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 };

var values= numbers.Where((n, index) => (index % 2) != 0).ToList();

foreach(int item in values)

{

      Console.WriteLine(item.Tostring())

}

Here: numbers.Where(Fun<int,bool>,predicate)

based on source(numbers).so delegate points to integers.

another example is

  var names = new[] { "app", "balu", "charan", "dhanush" };

IEnumerable<string> stringvalues = names.Where(s => s.Contains("charan")).ToList();

            foreach (string item in stringvalues)

            {

                Console.WriteLine(item.ToString());

            }

Here: names.Where(Fun<string,bool>,predicate);

As well in case of custom types like Students

List<Students> val = new List<Students>();

val.Add(new Students { Name = "aanand", Age = 22,City="Hyd" });

val.Add(new Students { Name = "balu", Age = 24,City="Pune" });

val.Add(new Students { Name = "charan", Age = 19,City="Bangalore" });

val.Add(new Students { Name = "dinesh", Age = 19, City="Hyd"});

or

// List<Students> val = new List<Students>(IEnumerable ier)

IEnumerable<Students> t = val.Where((Students, s1) => (Students.City == "Hyd"));----2nd predicate

--àt.Where(Fun<Student,int,bool>);

IEnumerable<Students> t = val.Where(Students => (Students.City == "Hyd"));

       --- 1st predicate

--àt.Where(Fun<Student,bool>,predicate);

And

1st predicate

(Students.City == "Hyd")-àreturn True/False.

Early loading/eagar loading:

index % 2 != 0

true

index % 2 != 0

false

index % 2 != 0

true

index % 2 != 0

false

index % 2 != 0

true

if students belongs to Hyd returns true other wise false.

2nd predicate

Val.Where((students,s1)=>(Students.City==”Hyd”));

if students belongs to Hyd returns true other wise false.

   foreach (Students item in t)

   {

       Console.WriteLine(item.Name+" "  +item.Age+"   "+item.City);

   }

Output:

1,3,8,21,55---intarray

Charan-----stringarray

Anand 22 Hyd

Dinesh 19 Hyd

s.Contains("charan")

false

s.Contains("charan")

false

s.Contains("charan")

true

s.Contains("charan")

false

s.Contains("charan")

The name 's' does not exist in the current context

above 2 are eagar/early loading.

Select Predicate:

List<Students> val = new List<Students>();

            val.Add(new Students { Name = "aanand", Age = 22, City = "Hyd" });

            val.Add(new Students { Name = "balu", Age = 24, City = "Pune" });

            val.Add(new Students { Name = "charan", Age = 19, City = "Bangalore" });

            val.Add(new Students { Name = "dinesh", Age = 19, City = "Hyd" });

   

 IEnumerable<Students> stuvalues = val.Select(r => r);

            foreach (Students item in stuvalues)

            {

                Console.WriteLine(item.City);

            }

2^nd predicate:

IEnumerable<string> stuvalues = val.Select(r => r.City);

or

IEnumerable<string> stuvalues = val.Select<Students, string>(r => r.City);

    foreach (string item in stuvalues)

   {

                Console.WriteLine(item.City);

   }

but

Lazy loading/deffered loading

Students.City=="Hyd"

false

Students.City=="Hyd"

True

Both perdicates: where and select

IEnumerable<Students> stuvalues = val.Where((Students, s1) => (Students.City == "Hyd")).Select(r => r);

or

IEnumerable<Students> stuvalues = val.Where((Students, s1) => (Students.City == "Hyd"));//.Select(r => r);

            foreach (Students item in stuvalues)

            {

                Console.WriteLine(item.City);

            }

IEnumerable<string> stuvalues = val.Where((Students, s1) => (Students.City == "Hyd")).Select(r => r.City);

            foreach (string item in stuvalues)

            {

                Console.WriteLine(item);

            }
Note: projection operator can be where/select.but the return type is should math
both the sites

we can know the return type of Linq query while showing

like

before writing select projection in linq query

after writing select projection in linq query