1. Mohammad Shaker
mohammadshaker.com
C# Programming Course
@ZGTRShaker
2011, 2012, 2013, 2014
C# Starter
L05 – LINQ and Lambda Expressions

2. LINQ

3. LINQ
One of the most awesome things ever done!

4. LINQ
Where’s Java?

5. LINQ
Where’s Java?
2013 with some tool (not as good as .NET)

6. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

7. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

8. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
List<string> queryResults = new List<string>();
foreach (var item in names)
{
if (n.StartsWith(“S”))
{
queryResults.Add(item);
}
}
var queryResults = from n in names
where n.StartsWith("S")
select n;

9. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
List<string> queryResults = new List<string>();
foreach (var item in names)
{
if (n.StartsWith(“S”))
{
queryResults.Add(item);
}
}
var queryResults = from n in names
where n.StartsWith("S")
select n;

10. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
List<string> queryResults = new List<string>();
foreach (var item in names)
{
if (n.StartsWith(“S”))
{
queryResults.Add(item);
}
}
var queryResults = from n in names
where n.StartsWith("S")
select n;
The SAME!

11. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
List<string> queryResults = new List<string>();
foreach (var item in names)
{
if (n.StartsWith(“S”))
{
queryResults.Add(item);
}
}
var queryResults = from n in names
where n.StartsWith("S")
select n;
The SAME!

12. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

13. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Smith
Smythe
Small
Singh
Samba
Program finished, press Enter/Return to continue:

14. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

15. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Alonso
Zheng
Smith
Jones
Smythe
Small
Ruiz
Hsieh
Jorgenson
Ilyich
Singh
Samba
Program finished, press Enter/Return to continue:

16. LINQ
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Alonso
Zheng
Smith
Jones
Smythe
Small
Ruiz
Hsieh
Jorgenson
Ilyich
Singh
Samba
Program finished, press Enter/Return to continue:

17. Lambda Expressions

18. Tons of code in a line

19. Lambda Expressions
• The operator => is called the lambda operator.
n => n < 1000
“ Lambda ” comes from the lambda calculus, the mathematical formalism underlying
functional programming languages, which are the kind of programming on which LINQ is
based. If you are interested, check out sources such as the Wikipedia article on lambda
calculus. You don ’ t need to understand the mathematics to use lambda functions, although
understanding functional programming is helpful for advanced LINQ programming.

20. Lambda Expressions
var queryResults = from n in names
where n.StartsWith("S")
select n;

21. Lambda Expressions
n => n.StartsWith(“S”)
var queryResults = from n in names
where n.StartsWith("S")
select n;

22. Lambda Expressions
n => n.StartsWith(“S”)
var queryResults = from n in names
where n.StartsWith("S")
select n;

23. Lambda Expressions
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = names.Where(n => n.StartsWith("S"));
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

24. Lambda Expressions
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = names.Where(n => n.StartsWith("S"));
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

25. Lambda Expressions
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = names.Where(n => n.StartsWith("S"));
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Smith
Smythe
Small
Singh
Samba
Program finished, press Enter/Return to continue:

26. Query Techniques

27. Ordering Query Results
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
orderby n
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

28. Ordering Query Results
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = from n in names
where n.StartsWith("S")
orderby n
select n;
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Samba
Singh
Small
Smith
Smythe
Program finished, press Enter/Return to continue:

29. Ordering Query Results
• Descending order
• This orders the example results as follows:
orderby n descending
Smythe
Smith
Small
Singh
Samba

30. Ordering Query Results
• Ordering Using Method Syntax
var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith(“S”));
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith("S"));
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}

31. Ordering Query Results
• Ordering Using Method Syntax
var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith(“S”));
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith("S"));
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Samba
Singh
Small
Smith
Smythe
Program finished, press Enter/Return to continue:

32. Ordering Query Results
• Ordering Using Method Syntax
var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith(“S”));
static void Main(string[] args)
{
string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe",
"Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"};
var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith("S"));
Console.WriteLine("Names beginning with S:");
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.Write("Program finished, press Enter/Return to continue:");
Console.ReadLine();
}
Names beginning with S:
Samba
Singh
Small
Smith
Smythe
Program finished, press Enter/Return to continue:
IOrderedEnumerable < string > and IEnumerable < string >

33. Ordering Query Results
• Descending order
var queryResults = names.OrderByDescending(n => n).Where(n => n.StartsWith(“S”));

34. Ordering Query Results
• What does this do?
var queryResults =
names.OrderBy(n => n.Substring(n.Length-1)).Where(n => n.StartsWith(“S”));

35. Ordering Query Results
• What does this do?
var queryResults =
names.OrderBy(n => n.Substring(n.Length-1)).Where(n => n.StartsWith(“S”));

36. Ordering Query Results
• What does this do?
var queryResults =
names.OrderBy(n => n.Substring(n.Length-1)).Where(n => n.StartsWith(“S”));

37. Querying Complex Objects

38. Querying Complex Objects
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
}

39. Querying Complex Objects
static void Main(string[] args)
{
List < Customer > customers = new List < Customer >
{
new Customer { ID=”A”, City=”New York”, Country=”USA”,Region=”North America”, Sales=9999},
new Customer { ID=”B”, City=”Mumbai”, Country=”India”,Region=”Asia”, Sales=8888 },
new Customer { ID=”C”, City=”Karachi”, Country=”Pakistan”,Region=”Asia”, Sales=7777 },
new Customer { ID=”D”, City=”Delhi”, Country=”India”,Region=”Asia”, Sales=6666 },
new Customer { ID=”E”, City=”S ã o Paulo”, Country=”Brazil”,Region=”South America”, Sales=5555 },
new Customer { ID=”F”, City=”Moscow”, Country=”Russia”,Region=”Europe”, Sales=4444 },
…
};
var queryResults =
from c in customers
where c.Region == “Asia”
select c;
Console.WriteLine(“Customers in Asia:”);
foreach (Customer c in queryResults)
{
Console.WriteLine(c);
}
Console.Write(“Program finished, press Enter/Return to continue:”);
Console.ReadLine();
}

40. Querying Complex Objects
• The output:
• Why?!
– Because ToString() is called for each Customer object. ToString() Is inherited directly
from the object class.
• Solution: Override the ToString() method.
Customers in Asia:
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
CSharpCourse2011.Customer
Program finished, press Enter/Return to continue:

41. Querying Complex Objects
• From this:
• To this:
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return “ID: “ + ID + “ City: “ + City + “ Country: “ + Country +
“ Region: “ + Region + “ Sales: “ + Sales;
}
}
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
}

42. Querying Complex Objects
• The output now is:
Customers in Asia:
ID: B City: Mumbai Country: India Region: Asia Sales: 8888
ID: C City: Karachi Country: Pakistan Region: Asia Sales: 7777
ID: D City: Delhi Country: India Region: Asia Sales: 6666
ID: G City: Seoul Country: Korea Region: Asia Sales: 3333
ID: H City: Istanbul Country: Turkey Region: Asia Sales: 2222
ID: I City: Shanghai Country: China Region: Asia Sales: 1111
ID: L City: Jakarta Country: Indonesia Region: Asia Sales: 3000
ID: M City: Tokyo Country: Japan Region: Asia Sales: 4000
ID: P City: Tehran Country: Iran Region: Asia Sales: 7000
ID: R City: Beijing Country: China Region: Asia Sales: 9000
Program finished, press Enter/Return to continue:

43. Querying Complex Objects
var queryResults =
from c in customers
where c.Region == “Asia”
select c.City;
Mumbai
Karachi
Delhi
Seoul
Istanbul
Shanghai
Jakarta
Tokyo
Tehran
Beijing

44. Selecting Multiple Properties

45. Querying Complex Objects
• Let’s see this:
select c.City, c.Country, c.Sales

46. Querying Complex Objects
• Let’s see this:
• It’s an error. Unlike in SQL, LINQ does not allow multiple fields in a select clause!
– So, what’s the solution?
• Just creating a new object on-the-fly in the select clause to hold the results you want for your query!
select c.City, c.Country, c.Sales

47. Querying Complex Objects
• Let’s see this:
• It’s an error. Unlike in SQL, LINQ does not allow multiple fields in a select clause!
– So, what’s the solution?
• Just creating a new object on-the-fly in the select clause to hold the results you want for your query!
select c.City, c.Country, c.Sales
var queryResults =
from c in customers
where c.Region == “North America”
select new { c.City, c.Country, c.Sales };
foreach (var item in queryResults)
{
Console.WriteLine(item);
}

48. Querying Complex Objects
• Let’s see this:
• It’s an error. Unlike in SQL, LINQ does not allow multiple fields in a select clause!
– So, what’s the solution?
• Just creating a new object on-the-fly in the select clause to hold the results you want for your query!
select c.City, c.Country, c.Sales
var queryResults =
from c in customers
where c.Region == “North America”
select new { c.City, c.Country, c.Sales };
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
{ City = New York, Country = USA, Sales = 9999 }
{ City = Mexico City, Country = Mexico, Sales = 2000 }
{ City = Los Angeles, Country = USA, Sales = 5000 }
Program finished, press Enter/Return to continue:

49. Querying Complex Objects
• Now, instead of all this:
• Let’s try this:
var queryResults = customers.Where(c => c.Region == “North America”)
.Select(c => new { c.City, c.Country, c.Sales });
var queryResults =
from c in customers
where c.Region == “North America”
select new { c.City, c.Country, c.Sales };
foreach (var item in queryResults)
{
Console.WriteLine(item);
}

50. Querying Complex Objects
• Now, instead of all this:
• Let’s try this:
var queryResults = customers.Where(c => c.Region == “North America”)
.Select(c => new { c.City, c.Country, c.Sales });
{ City = New York, Country = USA, Sales = 9999 }
{ City = Mexico City, Country = Mexico, Sales = 2000 }
{ City = Los Angeles, Country = USA, Sales = 5000 }
Program finished, press Enter/Return to continue:
var queryResults =
from c in customers
where c.Region == “North America”
select new { c.City, c.Country, c.Sales };
foreach (var item in queryResults)
{
Console.WriteLine(item);
}

51. Querying Complex Objects
• Now, instead of this:
• Let’s try this:
var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales })
.Where(c => c.Region == “North America”);
var queryResults = customers.Where(c => c.Region == “North America”)
.Select(c => new { c.City, c.Country, c.Sales });

52. Querying Complex Objects
• Now, instead of this:
• Let’s try this:
• It’s a Compiler Error! Because: The Region property is not included in the
anonymous type.
{c.City, c.Country, c.Sales } created by the Select() projection. The
compiler doesn’t know it yet!
var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales })
.Where(c => c.Region == “North America”);
var queryResults = customers.Where(c => c.Region == “North America”)
.Select(c => new { c.City, c.Country, c.Sales });

53. Querying Complex Objects
• OK, now, instead of this:
• Let’s try this:
var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales })
.Where(c => c.City == “New York”);
var queryResults = customers.Where(c => c.Region == “North America”)
.Select(c => new { c.City, c.Country, c.Sales });

54. Querying Complex Objects
• OK, now, instead of this:
• Let’s try this:
• Works beautifully!
var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales })
.Where(c => c.City == “New York”);
var queryResults = customers.Where(c => c.Region == “North America”)
.Select(c => new { c.City, c.Country, c.Sales });

55. Querying Complex Objects
• Distinct
var queryResults = customers.Select(c => c.Region).Distinct();
var queryResults = (from c in customers select c.Region).Distinct();

56. Ordering By Multiple Levels

57. Ordering By Multiple Levels
var queryResults =
from c in customers
orderby c.Region, c.Country, c.City
select new { c.ID, c.Region, c.Country, c.City };

58. Ordering By Multiple Levels
var queryResults =
from c in customers
orderby c.Region, c.Country, c.City
select new { c.ID, c.Region, c.Country, c.City };
{ ID = O, Region = Africa, Country = Egypt, City = Cairo }
{ ID = J, Region = Africa, Country = Nigeria, City = Lagos }
{ ID = R, Region = Asia, Country = China, City = Beijing }
{ ID = I, Region = Asia, Country = China, City = Shanghai }
{ ID = D, Region = Asia, Country = India, City = Delhi }
{ ID = B, Region = Asia, Country = India, City = Mumbai }
{ ID = L, Region = Asia, Country = Indonesia, City = Jakarta }
{ ID = P, Region = Asia, Country = Iran, City = Tehran }
{ ID = M, Region = Asia, Country = Japan, City = Tokyo }
{ ID = G, Region = Asia, Country = Korea, City = Seoul }
….

59. Drilling further
• Many other techniques
• Grouping
• Joining
• Take
• Skip
• ….