The document discusses the evolution of LINQ (Language Integrated Query) in .NET from version 1.0 through 3.5, including the introduction of lambda expressions and extension methods. It provides examples of LINQ queries on collections, joining data from multiple sources, and creating custom extension methods.

1. Chuck Durfee, 3 October 2012

4. BIG
DATA

8. Enumerable.Select(
Enumerable.OrderBy(
Enumerable.Where(names, s => s.Length == 5),
s => s
),
s => s.ToUpper()
);
versus
names.Where(s => s.Length == 5)
.OrderBy(s => s)
.Select(s => s.ToUpper())

10. , my dear Watson

12. 1.0
delegate bool FilterMethod(string s);
private bool IsFiveLetterName(string s) {
return s.Length == 5;
}
public DotNet10Land()
{
FilterMethod filter = IsFiveLetterName;
}

13. 2.0
delegate bool FilterMethod(string s);
public DotNet20Land()
{
FilterMethod filter =
delegate(string s) {
return s.Length == 5;
};
}

14. C# 3 = .NET 3.5
delegate bool FilterMethod(string s);
public DotNet35Land()
{
string chuck = "chuck";
FilterMethod filter =
delegate(string s) {
return s != chuck && s.Length == 5;
};
}

16. Func
// delegate bool FilterMethod(string s);
public DotNet35Land()
{
Func<string, bool> filter =
delegate(string s) {
return s.Length == 5;
};
}

17. Func<string, bool>
Func<string, int, DateTime>
Func<List<string>, int, bool>
but not
Func<string, System.Void>

18. and… Action
// delegate void ActionMethod(string s);
public DotNet35Land()
{
Action<string> action = delegate(string s) {
if (s.Length != 5)
throw new ArgumentException("Length != 5");
};
}

19. LAMBDA EXPRESSIONS
Func<string, bool> filter =
delegate(string s) {return s.Length == 5;};
var filter = (string s) => {return s.Length == 5;};
var filter = (string s) => s.Length == 5;
var filter = (s) => s.Length == 5;
var filter = s => s.Length == 5;

20. by Alonzo Church, 1930’s

32. string[] names = { "Tom", "Dick",
"Harry" };
names.Select((s, i) =>
(i + 1) + "=" + s);
1=Tom
2=Dick
3=Harry

34. int[] numbers = { 3, 5, 7 };
string[] words = { "three", "five",
"seven", "ignored" };
IEnumerable<string> zip = 3=three
numbers.Zip(words, 5=five
(n, w) => n + "=" + w); 7=seven

36. IEnumerable<Order> spanishOrders =
customers
.Where(c => c.Country == "Spain")
.SelectMany(c => c.Orders);

38. var slowQuery =
from c in customers
from p in purchases where c.ID == p.CustomerID
select c.Name + " bought a " + p.Description;
var fastQuery =
from c in customers
join p in purchases on c.ID equals p.CustomerID
select c.Name + " bought a " + p.Description;

40. var easyToRead =
from c in customers
join p in purchases on c.ID equals p.CustomerID
select c.Name + " bought a " + p.Description;
var harderToRead = customers.Join (
purchases,
c => (int?)(c.ID),
p => p.CustomerID,
(c, p) => ((c.Name + " bought a ") +
p.Description)
);

43. public static class EnumerableExtensions
{
public static string ToCsv<T>(
this IEnumerable<T> sequence)
{
const string delimiter = ", ";
return sequence.Aggregate(
new StringBuilder(),
(sb, s) => sb.Append(s + delimiter),
sb => sb.ToString()
.TrimEnd(delimiter.ToArray()));
}
}
new[] { 1, 2, 3, 5, 8, 13, 20 } => 1, 2, 3, 5, 8, 13, 20

45. Chuck Durfee
http://neontapir.com