LINQ quick start

// Student collection
IList<Student> studentList = new List<Student>>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 13} ,
        new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
        new Student() { StudentID = 4, StudentName = "Ram" , Age = 20} ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 15 } 
    };

// LINQ Query Syntax to find out teenager students
var teenAgerStudent = from s in studentList
                      where s.Age > 12 && s.Age < 20
                      select s; // no library need built into the lang
                      
                      //method based linq
                      // string collection
IList<string> stringList = new List<string>() { 
    "C# Tutorials",
    "VB.NET Tutorials",
    "Learn C++",
    "MVC Tutorials" ,
    "Java" 
};

// LINQ Query Syntax
var result = stringList.Where(s => s.Contains("Tutorials")); //needs library system.net


all linq methods where implemented as extesion in the linq namspece in a class called enumerable, these can work on any 

use firstordefault so you don't a run time error when oan object returned is null

foundCust = custList.FirstOrDefault(c => {
Debug.WriteLine(c.name)
return c.id == custid
});//lamda expression

//skip 1 and select the second
c.Where(b => b ==2).Skip(1).First()

linq provides transversal, filter and expression

namespace ExtensionMethods
{
    public static class MyExtensions
    {
        public static int WordCount(this String str)
        {
            return str.Split(new char[] { ' ', '.', '?' }, 
                             StringSplitOptions.RemoveEmptyEntries).Length;
        }
    }   
}

using ExtensionMethods
string s = "Hello Extension Methods";  
int i = s.WordCount();


OrderBy	The operator sort values in an ascending order	orderby	Order By
OrderByDescending	The operator sort values in a descending order	orderby ... descending	Order By ... Descending
ThenBy	Executes a secondary sorting in an ascending order	orderby …, …	Order By …, …
ThenByDescending	Executes a secondary sorting in a descending order	orderby …, … descending	Order By …, … Descending
Reverse	Performs a reversal of the order of the elements in a collection	


two great testing tools
  var ran = new Random();
  
   3: // does this generate 100 random numers?  
   4: // Or repeat first random number 100 times?
    var repeatedRandom = Enumerable.Repeat(ran.Next(), 100);
 
  var numbers = Enumerable.Range(1, 10).ToList();
  
  linq set operators
  intersect - will find the items that are == in two list
  except - wil give you the items not in the second list
  concat - will merge sets
  distinct - will give just that
  union - will merge the unqiue items 
  
  join and create a new list and project new result
  var results = workOrders.Join(plans,
  wo => wo.WorkOrderNumber,
  p => p.WorkOrderNumber,
  (order,plan) => new {order.WorkOrderNumber, order.WorkDescription, plan.ScheduledDate}
); // this will return a enumerable with three properties work WorkOrderNumber WorkDescription ScheduledDate

//when we want to work with a collection within another collection we can use selectmany to flatten the object
// Select gets a list of lists of phone numbers
IEnumerable<IEnumerable<PhoneNumber>> phoneLists = people.Select(p => p.PhoneNumbers); // non flattened so you have an enumarble inside of another

// SelectMany flattens it to just a list of phone numbers. // now only one enumberable

//math with lamda
max - persons.Max(p => p.age);
min - persons.Min(p => p.age);
average - persons.Average(p => p.age);
any - persons.Any(p => p.age); // lazy check will only peek first rather than look at all items
count - persons.Count(p => p.age); // not lazy will count all


//group by and aggreagate
List<ResultLine> result = Lines
    .GroupBy(l => l.ProductCode)
    .Select(cl => new ResultLine
            {
                ProductName = cl.First().Name,
                Quantity = cl.Count().ToString(),
                Price = cl.Sum(c => c.Price).ToString(),
            }).ToList(); // when you group you only get one so you aggreate to get a true group by 
            
            

IEnumerable<PhoneNumber> phoneNumbers = people.SelectMany(p => p.PhoneNumbers);