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C# Lambda Expression Examples
using System;
using System.Collections.Generic;
using System.Linq;
namespace ygunayer
{
public class Lambdas
{
static void Main(string[] args)
{
var p = new Lambdas();
p.SomeMethod();
p.SomeOtherMethod();
p.SomeLambdaMethodCaller();
p.SomeLambdaGeneratorCaller();
p.MapExample();
p.FlatMapExample();
p.FilterExample();
p.SkipExample();
p.LimitExample();
p.DistinctExample();
p.SortExample();
p.ReduceExample();
Console.ReadKey();
}
public void SomeMethod()
{
Action<string, string, string> foo = (a, b, c) =>
{
Console.WriteLine(a + ", " + b + " and " + c);
};
// outputs "One, Two and Three"
foo("One", "Two", "Three");
// outputs "Six, Nine and Ten"
foo("Six", "Nine", "Ten");
}
public void SomeOtherMethod() {
Func<int, int, string> foo = (a, b) => {
return "The product of " + a + " and " + b + " is " + (a * b);
};
string foo1 = foo(5, 10);
string foo2 = foo(3, 5);
// outputs "The product of 5 and 10 is 50"
Console.WriteLine(foo1);
// outputs "The product of 3 and -5 is -15"
Console.WriteLine(foo2);
}
public void SomeLambdaMethodExecutor(Func<int, int, int> fn)
{
Console.WriteLine("Result of fn(1, 2) is " + fn(1, 2));
}
public void SomeLambdaMethodCaller()
{
Func<int, int, int> add = (a, b) => { return a + b; };
// this is also valid
Func<int, int, int> multiply = (a, b) => a * b;
// outputs "Result of fn(1, 2) is 3"
SomeLambdaMethodExecutor(add);
// outputs "Result of fn(1, 2) is 2"
SomeLambdaMethodExecutor(multiply);
}
public Func<int, int, int> SomeLambdaGenerator(string which)
{
if (which == "add")
return (a, b) => { return a + b; };
else
return (a, b) => { return a * b; };
}
public void SomeLambdaGeneratorCaller()
{
Func<int, int, int> add = SomeLambdaGenerator("add");
Func<int, int, int> multiply = SomeLambdaGenerator("multiply");
// outputs "1 + 2 = 3"
Console.WriteLine("1 + 2 = " + add(1, 2));
// outputs "1 * 2 = 2"
Console.WriteLine("1 * 2 = " + multiply(1, 2));
}
public void MapExample()
{
var numbers = new List<int>() { 1, 2, 3, 4, 5 };
var mapped = numbers.Select(number => number * 5).ToList();
// outputs "5, 10, 15, 20, 25"
Console.WriteLine(string.Join(", ", mapped));
}
public void FlatMapExample()
{
var john = new Person()
{
Name = "John",
Addresses = new List<string>() { "John's Home", "John's Office" },
Age = 26
};
var mary = new Person()
{
Name = "Mary",
Addresses = new List<string>() { "Mary's Home" },
Age = 25
};
var people = new List<Person>() { john, mary };
// the type of this object is List<List<string>> which is obviously incorrect
var incorrect = people.Select(person => person.Addresses).ToList();
var allAddresses = people.SelectMany(person => person.Addresses).ToList();
// outputs two lists which is incorrect, we want a list of all addresses
Console.WriteLine(string.Join(", ", incorrect));
// outputs "John's Home, John's Office, Mary's Home"
Console.WriteLine(string.Join(", ", allAddresses));
}
public void FilterExample()
{
var numbers = new List<int>() { 1, 2, 3, 4, 5 };
var odds = numbers.Where(number => number % 2 == 1).ToList();
// outputs "1, 3, 5"
Console.WriteLine(string.Join(", ", odds));
}
public void SkipExample()
{
var numbers = new List<int>() { 1, 2, 3, 4, 5 };
var remainder = numbers.Skip(3).ToList();
// outputs "4, 5"
Console.WriteLine(string.Join(", ", remainder));
}
public void LimitExample()
{
var numbers = new List<int>() { 1, 2, 3, 4, 5 };
var taken = numbers.Take(3).ToList();
// outputs "1, 2, 3"
Console.WriteLine(string.Join(", ", taken));
}
public void DistinctExample()
{
var numbers = new List<int>() { 1, 1, 2, 3, 5 };
var distinct = numbers.Distinct().ToList();
// outputs "1, 2, 3, 5"
Console.WriteLine(string.Join(", ", distinct));
}
public void SortExample()
{
var john = new Person()
{
Name = "John",
Addresses = new List<string>() { "John's Home", "John's Office" },
Age = 26
};
var mary = new Person()
{
Name = "Mary",
Addresses = new List<string>() { "Mary's Home" },
Age = 25
};
var sean = new Person()
{
Name = "Sean",
Addresses = new List<string>() { "Sean's Home" },
Age = 33
};
var people = new List<Person>() { john, mary, sean };
// sorts people to their ages in a descending order
var sorted = people.OrderByDescending(x => x.Age).ToList();
// outputs "Sean (33), John (26), Mary (25)"
Console.WriteLine(string.Join(", ", sorted));
}
public void ReduceExample()
{
var numbers = new List<int>() { 1, 2, 3, 4, 5 };
var sum = numbers.Aggregate(50, (a, b) => a + b);
// we can emulate IEnumerable.ToList() using the reduce operation!
var asList = numbers.Aggregate(new List<int>(), (list, number) =>
{
list.Add(number);
return list;
});
// outputs "65"
Console.WriteLine(sum);
// outputs "1, 2, 3, 4, 5"
Console.WriteLine(string.Join(", ", asList));
}
}
public class Person
{
public string Name { get; set; }
public List<string> Addresses { get; set; }
public int Age { get; set; }
public override string ToString()
{
return Name + " (" + Age + ")";
}
}
}
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