Difference: UsingCSharpOnPatas (1 vs. 13)

the[6] of[3] and[3] establish[2] for[2] states[2] to[2] united[2] perfect[1] promote[1] general[1] we[1]

10. Using the GroupBy LINQ operator

We have found that, even with the new release 2.4.2 of Mono, the GroupBy operator is much slower than it is on .NET. It is to be expected that you will find some differences in performance between the Microsoft and Mono implementations. In the case of GroupBy, you can always break the operation in two steps, using a temporary dictionary, for example.

Keeping this limitation in mind, here is the example I presented at the 2009 CLMA orientation talk on C#. This complete program reads an HTML file with the complete text of "Moby Dick," strips out HTML tags using a regular expression, and then prints a "graphical" Zipf distribution (word-frequency histogram) of the 35 most common words onto your console.

using System;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

class MainClass
{
	static void Main()
	{
		String text = new StreamReader("moby_dick.html").ReadToEnd();

		text = Regex.Replace(text, "<(.|\n)*?>", String.Empty);

		String[] words = text.Split(" \n\",.;-!?".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);

var tallies = words .GroupBy(w => w.ToLower()) .Select(g => new { g.Key, Tally = g.Count() }) .OrderByDescending(e => e.Tally);

int scale = tallies.First().Tally / 60; foreach (var tally in tallies.Take(35)) WriteLine ("{0,6} {1}", tally.Key, new String('*', tally.Tally / scale)); } };

11. More Information

A recording of the treehouse presentation "Using C# on Patas" can be found here: http://uweoconnect.extn.washington.edu/p30062745/. The slides from this talk are on patas at /opt/dropbox/09-10/orientation/Mono_on_Patas.pdf.

Most of the code examples on this page, along with the "Moby Dick" text, can be found on patas in the following directory: /opt/dropbox/09-10/orientation/csharp-demos

The best book on LINQ that I've found is "Pro LINQ: Language Integrated Query in C# 2008" by Joseph C. Rattz, Jr. (APress 1-59059-789-3). This book presupposes familiarity with C#.

-- Main.gslayden - 28 Oct 2009

12. Discussion

-----Original Message-----
From: patas-announce-bounces@mailman2.u.washington.edu On Behalf Of brodb@u
Sent: Thursday, October 15, 2009 3:34 PM
To: patas-announce@u.washington.edu
Subject: [patas-announce] Mono upgraded to 2.4.2.3.

I've updated our local build of Mono, in /opt/mono/bin, to 2.4.2.3.  Mono Debugger (mdb) version 2.4.2.1 is also installed there.

The old version remains available in /opt/mono-2.0.1/bin, if you need it.

 using System;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		Console.WriteLine("hello world");
 	}
 }
 

 gmcs hello.cs
 mono hello.exe
 

 mono compiled_by_msvc.exe
 

 universe	= vanilla
 getenv		= true
 executable	= /opt/mono/bin/mono
 arguments	= "myprogram.exe -myarg1 -myarg2"
 input		= mystdin.txt
 output		= mystdout.txt
 error		= mystderr.txt
 log		= /tmp/myuwid.log
 transfer_executable = false
 queue
 

 using System;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String s = "1.\tThis is a string.";
 		String[] string_arr = s.Split('\t');
 
 		Char[] trim_chars = ".:;,".ToCharArray();
 		String ns = string_arr[0].Trim(trim_chars);
 		int i = Convert.ToInt32(ns);
 
 		Console.WriteLine(i);
 
 		foreach (String s2 in string_arr[1].Split())
 			Console.WriteLine(s2.Replace('s','z'));
 	}
 }
 

 1
 Thiz
 iz
 a
 ztring.
 

 using System;
 using System.IO;
 using System.Linq;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String my_filename = "the_file.txt";
 
 		String data = "Four score and seven years ago.";
 
 		// Write some data to the file
 		int i = 0;
 		using (FileStream fs = new FileStream(my_filename, FileMode.Create, FileAccess.Write, FileShare.None))  
 		{
 			using (StreamWriter sr = new StreamWriter(fs, Encoding.GetEncoding(28591)))	// Latin-1
 			{
 				foreach (String s in data.Split())
 					sr.WriteLine((++i).ToString() + ". " + new String(s.ToCharArray().Reverse  ().ToArray()));
 			}
 		}
 
 		// Read data from the file
 		using (FileStream fs = File.Open(my_filename, FileMode.Open, FileAccess.Read, FileShare.Read))
 		{
 			using (StreamReader sr = new StreamReader(fs, Encoding.GetEncoding(28591)))
 			{
 				String s;
 				while (null != (s = sr.ReadLine()))
 					Console.WriteLine(s);
 			}
 		}
 	}
 }
 

 1. ruoF
 2. erocs
 3. dna
 4. neves
 5. sraey
 6. .oga
 

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
 public class MyObject
 {
 	public Double d_x;
 	public Double d_y;
 	public Double d_z;
 
 	// constructor
 	public MyObject(Double x_arg, Double y_arg, Double z_arg)
 	{
 		d_x = x_arg; d_y = y_arg; d_z = z_arg;
 	}
 };
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		Dictionary<String, MyObject> ht = new Dictionary<String, MyObject>();
 
 		ht.Add("object 1", new MyObject(3.0, 2.1, Math.PI));
 		ht.Add("object 2", new MyObject(Math.Sqrt(2.0), Math.Log(6.0,10.0), 3.2));
 		ht.Add("3rd object", new MyObject(2.1, 9.9, Double.NaN));
 
 		Console.WriteLine(ht["object 2"].d_x);
 	}
 }
 

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String text = "We the People of the United States, in Order to " +
 		"form a more perfect Union, establish Justice, ensure domestic " +
 		"Tranquility, provide for the common defence, promote the general " +
 		"Welfare, and secure the Blessings of Liberty to ourselves and our " +
 		"Posterity, do ordain and establish this Constitution for the United " +
 		"States of America.";
 
 		Char[] split_chars = new Char[] { '.', ',', ' ' };
 		String[] words = text.ToLower().Split(split_chars,StringSplitOptions.RemoveEmptyEntries);
 
 		// use a hash table to tally word-types:
 		Dictionary<String, int> hash_tab = new Dictionary<String, int>();
 		foreach (String w in words)
 		{
 			int v;
 			if (hash_tab.TryGetValue(w,out v))
 				hash_tab[w] = v+1;
 			else
 				hash_tab.Add(w,1);
 		}
 
 		// demonstrate using LINQ to display 12 of the most common word-types plus their counts
 		KeyValuePair<String, int>[] kvp_arr = hash_tab.OrderByDescending(e => e.Value).Take  (12).ToArray();
 		// this is similar to 'list comprehension' in Python
 		String s = kvp_arr.Aggregate(String.Empty,(av, e) => av + e.Key + "[" + e.Value + "] ");
 		Console.WriteLine(s);
 	}
 }
 

 using System;
 using System.IO;
 using System.Text;
 using System.Net;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String s;
 		using (WebClient wc = new WebClient())
 		{
 			using (Stream str = wc.OpenRead("http://www.compling.washington.edu/compling/"))
 			{
 				using (StreamReader sr = new StreamReader(str))
 					s = sr.ReadToEnd();
 			}
 		}
 		Console.WriteLine(s);
 	}
 }
 

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(string[] args)
 	{
 		String[] items = { "cat", "pear", "apple", "cat", "banana", "pear", "pear", "apple" };
 
 		KeyValuePair[] tallies = items.GroupBy(k => k, e => 1)
 				.Select(f => new KeyValuePair<String, int>(f.Key.ToUpper(), f.Sum()))
 				.OrderBy(g => g.Key)
 				.ToArray();
 
 		foreach (KeyValuePair<String, int> kvp in tallies)
 			Console.WriteLine(kvp.Key + '\t' + kvp.Value);
 	}
 }
 

 APPLE   2
 BANANA  1
 CAT     2
 PEAR    3
 

 using System;
 using System.IO;
 using System.Diagnostics;
 
 class MainClass
 {
 	public static void Main(string[] args)
 	{
 		ProcessStartInfo psi = new ProcessStartInfo();
 		psi.FileName = "python";
 		psi.Arguments = "test.py";
 		psi.RedirectStandardOutput = true;
 		psi.UseShellExecute = false;
 
 		using (Process p = new Process())
 		{
 			p.StartInfo = psi;
 			p.Start();
 
 			Console.WriteLine(p.StandardOutput.ReadToEnd());
 		}
 	}
 }
 

 using System;  using System.Text;    static class MainClass  {     static void Main(String[] args)     {        Console.WriteLine("hello world");     }  }  

 gmcs hello.cs  mono hello.exe  

 mono compiled_by_msvc.exe  

 universe   = vanilla  getenv      = true  executable   = /opt/mono/bin/mono  arguments   = "myprogram.exe -myarg1 -myarg2"  input      = mystdin.txt  output      = mystdout.txt  error      = mystderr.txt  log      = /tmp/myuwid.log  transfer_executable = false  queue  

 using System;  using System.Text;    static class MainClass  {     static void Main(String[] args)     {        String s = "1.\tThis is a string.";        String[] string_arr = s.Split('\t');          Char[] trim_chars = ".:;,".ToCharArray();        String ns = string_arr[0].Trim(trim_chars);        int i = Convert.ToInt32(ns);          Console.WriteLine(i);          foreach (String s2 in string_arr[1].Split())           Console.WriteLine(s2.Replace('s','z'));     }  }  

 1  Thiz  iz  a  ztring.  

 using System;  using System.IO;  using System.Linq;  using System.Text;    static class MainClass  {     static void Main(String[] args)     {        String my_filename = "the_file.txt";          String data = "Four score and seven years ago.";          // Write some data to the file        int i = 0;        using (FileStream fs = new FileStream(my_filename, FileMode.Create, FileAccess.Write, FileShare.None))          {           using (StreamWriter sr = new StreamWriter(fs, Encoding.GetEncoding(28591)))   // Latin-1           {              foreach (String s in data.Split())                 sr.WriteLine((++i).ToString() + ". " + new String(s.ToCharArray().Reverse  ().ToArray()));           }        }          // Read data from the file        using (FileStream fs = File.Open(my_filename, FileMode.Open, FileAccess.Read, FileShare.Read))        {           using (StreamReader sr = new StreamReader(fs, Encoding.GetEncoding(28591)))           {              String s;              while (null != (s = sr.ReadLine()))                 Console.WriteLine(s);           }        }     }  }  

 1. ruoF  2. erocs  3. dna  4. neves  5. sraey  6. .oga  

 using System;  using System.Collections.Generic;  using System.Linq;  using System.Text;    public class MyObject  {     public Double d_x;     public Double d_y;     public Double d_z;       // constructor     public MyObject(Double x_arg, Double y_arg, Double z_arg)     {        d_x = x_arg; d_y = y_arg; d_z = z_arg;     }  };    static class MainClass  {     static void Main(String[] args)     {        Dictionary<String, MyObject> ht = new Dictionary<String, MyObject>();          ht.Add("object 1", new MyObject(3.0, 2.1, Math.PI));        ht.Add("object 2", new MyObject(Math.Sqrt(2.0), Math.Log(6.0,10.0), 3.2));        ht.Add("3rd object", new MyObject(2.1, 9.9, Double.NaN));          Console.WriteLine(ht["object 2"].d_x);     }  }  

 using System;  using System.Collections.Generic;  using System.Linq;  using System.Text;    static class MainClass  {     static void Main(String[] args)     {        String text = "We the People of the United States, in Order to " +        "form a more perfect Union, establish Justice, ensure domestic " +        "Tranquility, provide for the common defence, promote the general " +        "Welfare, and secure the Blessings of Liberty to ourselves and our " +        "Posterity, do ordain and establish this Constitution for the United " +        "States of America.";          Char[] split_chars = new Char[] { '.', ',', ' ' };        String[] words = text.ToLower().Split(split_chars,StringSplitOptions.RemoveEmptyEntries);          // use a hash table to tally word-types:        Dictionary<String, int> hash_tab = new Dictionary<String, int>();        foreach (String w in words)        {           int v;           if (hash_tab.TryGetValue(w,out v))              hash_tab[w] = v+1;           else              hash_tab.Add(w,1);        }          // demonstrate using LINQ to display 12 of the most common word-types plus their counts        KeyValuePair<String, int>[] kvp_arr = hash_tab.OrderByDescending(e => e.Value).Take  (12).ToArray();        // this is similar to 'list comprehension' in Python        String s = kvp_arr.Aggregate(String.Empty,(av, e) => av + e.Key + "[" + e.Value + "] ");        Console.WriteLine(s);     }  }  

 using System;  using System.IO;  using System.Text;  using System.Net;    static class MainClass  {     static void Main(String[] args)     {        String s;        using (WebClient wc = new WebClient())        {           using (Stream str = wc.OpenRead("http://www.compling.washington.edu/compling/"))           {              using (StreamReader sr = new StreamReader(str))                 s = sr.ReadToEnd();           }        }        Console.WriteLine(s);     }  }  

 using System;  using System.Collections.Generic;  using System.Linq;  using System.Text;    static class MainClass  {     static void Main(string[] args)     {        String[] items = { "cat", "pear", "apple", "cat", "banana", "pear", "pear", "apple" };          KeyValuePair[] tallies = items.GroupBy(k => k, e => 1)              .Select(f => new KeyValuePair<String, int>(f.Key.ToUpper(), f.Sum()))              .OrderBy(g => g.Key)              .ToArray();          foreach (KeyValuePair<String, int> kvp in tallies)           Console.WriteLine(kvp.Key + '\t' + kvp.Value);     }  }  

 APPLE   2  BANANA  1  CAT     2  PEAR    3  

 using System;  using System.IO;  using System.Diagnostics;    class MainClass  {     public static void Main(string[] args)     {        ProcessStartInfo psi = new ProcessStartInfo();        psi.FileName = "python";        psi.Arguments = "test.py";        psi.RedirectStandardOutput = true;        psi.UseShellExecute = false;          using (Process p = new Process())        {           p.StartInfo = psi;           p.Start();             Console.WriteLine(p.StandardOutput.ReadToEnd());        }     }  }  

Unfortunately, support for non-RPM-based distributions is pretty slim. Mono is a Novell project, so they focus mainly on SuSE, their own Linux distribution. There is a Debian package, though, and since Ubuntu is Debian-derived, it's possible you could get that to work.

You could also experiment with some of the RPMs here, and see if any of them will install using "alien": http://download.opensuse.org/repositories/Mono/ Note that many of these are for mono 1.9.x. To get 2.x on patas I had to build it from source.

-- brodbd - 30 Dec 2008

 gmcs hello.cs
 mono hello.exe
 

 mono compiled_by_msvc.exe
 

 1
 Thiz
 iz
 a
 ztring.
 

 1. ruoF
 2. erocs
 3. dna
 4. neves
 5. sraey
 6. .oga
 

ht.Add("object 1", new MyObject (3.0, 2.1, Math.PI)); ht.Add("object 2", new MyObject (Math.Sqrt(2.0), Math.Log(6.0,10.0), 3.2)); ht.Add("3rd object", new MyObject (2.1, 9.9, NaN ));

 APPLE   2
 BANANA  1
 CAT     2
 PEAR    3
 

 gmcs hello.cs  mono hello.exe  

 mono compiled_by_msvc.exe  

{     

 1  Thiz  iz  a  ztring.  

 1. ruoF  2. erocs  3. dna  4. neves  5. sraey  6. .oga  

     static void Main(String[] args)

     {

        Dictionary<String, MyObject> ht = new Dictionary<String, MyObject>();

        ht.Add("object 1", new MyObject(3.0, 2.1, Math.PI));

        ht.Add("object 2", new MyObject(Math.Sqrt(2.0), Math.Log(6.0,10.0), 3.2));

        ht.Add("3rd object", new MyObject(2.1, 9.9, Double.NaN));

 APPLE   2  BANANA  1  CAT     2  PEAR    3  

My chances of adopting c# as my language of choice on Linux are pretty slim unless I can a good install of mono to run on my home version of Linux.

-- Main.andyf - 24 Nov 2008

 mono compiled_by_msvc.exe
 

 1
 Thiz
 iz
 a
 ztring.
 

9. Calling a Python Script as a Shell Process

 using System;
 using System.IO;
 using System.Diagnostics;
 
 class MainClass
 {
 	public static void Main(string[] args)
 	{
 		ProcessStartInfo psi = new ProcessStartInfo();
 		psi.FileName = "python";
 		psi.Arguments = "test.py";
 		psi.RedirectStandardOutput = true;
 		psi.UseShellExecute = false;
 
 		using (Process p = new Process())
 		{
 			p.StartInfo = psi;
 			p.Start();
 
 			Console.WriteLine(p.StandardOutput.ReadToEnd());
 		}
 	}
 }
 

7. Access a Web Page

 using System;
 using System.IO;
 using System.Text;
 using System.Net;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String s;
 		using (WebClient wc = new WebClient())
 		{
 			using (Stream str = wc.OpenRead("http://www.compling.washington.edu/compling/"))
 			{
 				using (StreamReader sr = new StreamReader(str))
 					s = sr.ReadToEnd();
 			}
 		}
 		Console.WriteLine(s);
 	}
 }
 

8. LINQ Operations

 universe	= vanilla
 getenv		= true
 executable	= /opt/mono/bin/mono
 arguments	= "myprogram.exe -myarg1 -myarg2"
 input		= mystdin.txt
 output		= mystdout.txt
 error		= mystderr.txt
 log		= /tmp/myuwid.log
 transfer_executable = false
 queue
 

6. Generic Collections

C# has a number of powerful strongly-typed generic collection objects. For example:

The following example shows how to use a generic Dictionary<String,int> to perform a very common Computational Linguistics operation, tallying the unique word-types in some text.

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String text = "We the People of the United States, in Order to " +
 		"form a more perfect Union, establish Justice, ensure domestic " +
 		"Tranquility, provide for the common defence, promote the general " +
 		"Welfare, and secure the Blessings of Liberty to ourselves and our " +
 		"Posterity, do ordain and establish this Constitution for the United " +
 		"States of America.";
 
 		Char[] split_chars = new Char[] { '.', ',', ' ' };
 		String[] words = text.ToLower().Split(split_chars,StringSplitOptions.RemoveEmptyEntries);
 
 		// use a hash table to tally word-types:
 		Dictionary<String, int> hash_tab = new Dictionary<String, int>();
 		foreach (String w in words)
 		{
 			int v;
 			if (hash_tab.TryGetValue(w,out v))
 				hash_tab[w] = v+1;
 			else
 				hash_tab.Add(w,1);
 		}
 
 		// demonstrate using LINQ to display 12 of the most common word-types plus their counts
 		KeyValuePair<String, int>[] kvp_arr = hash_tab.OrderByDescending(e => e.Value).Take(12).ToArray();
 		String s = kvp_arr.Aggregate(String.Empty,(av, e) => av + e.Key + "[" + e.Value + "] ");
 		Console.WriteLine(s);
 	}
 }
 

Result:

 the[6] of[3] and[3] establish[2] for[2] states[2] to[2] united[2] perfect[1] promote[1] general[1] we[1] 

7. LINQ Operations

As in many other modern languages, the C# String type is immutable. This allows for significant internal optimizations in the runtime environment but can be inefficient when doing intensive mutation and other editing operations. For this reason, the CLR also implements the StringBuilder object, which allows a large amount of text to be gathered through appending.

Strings can also be edited by converting them to an array of Char, as shown in the next example. The example also shows how a String object can be created from an array of Char.

 1. ruoF
 2. erocs
 3. dna
 4. neves
 5. sraey
 6. .oga
 

Using C# on Patas

C# is a powerful general-purpose programming language originally developed by Microsoft. After its approval as a standard by ECMA, it has been independently re-engineered as an open-source implementation which is available on many platforms, including Linux. It is installed and available for use on patas.

Because the mono implementation is extremely compatible, Console-oriented C# programs developed on Windows machines (i.e. with Visual Studio) will typically run on mono without changing the source code. (It is beyond the scope of this document to discuss the compatibility of graphical programs.)

C# programs operate in a fully sandboxed runtime environment which provides garbage-collection. As in Java, Python, and other high-level general-purpose languages, disposal of unused memory objects is tracked and managed by the system, relieving an enormous burden from the application programmer.

1. Sample Program

using System;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		Console.WriteLine("hello world");
 	}
 }
 

To compile on patas:

gmcs hello.cs
 mono hello.exe
 

The reason that this is a two-step process hints at the power of C# over interpreted languages; the first step "compiles" your source file into an intermediate byte-code called MSIL which is later processed by a runtime environment, called the Common Language Runtime, or CLR. This type of virtual instruction set is nothing new in computer science. But an innovation that Microsoft's CLR introduced was that this MSIL code is translated, on an as-needed basis, into actual native machine instructions for the target system. And it's retained in this optimal form as the program runs. This is called Just-in-time, or JIT compilation, and it means that your C# program runs with the performance of true native compilation.

2. Documentation

Microsoft's detailed commercial-quality documentation on C# is available freely on the web. Of primary interest will be the extensive CLR (".NET Framework") class libraries, which provide a wide array of system services and data structures. The mono project also offers a set of documentation.

mono - Documentation Library
MSDN - C# Language Reference
MSDN - .NET Framework Class Library

3. String Manipulation

using System;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String s = "1.\tThis is a string.";
 		String[] string_arr = s.Split('\t');
 
 		Char[] trim_chars = ".:;,".ToCharArray();
 		String ns = string_arr[0].Trim(trim_chars);
 		int i = Convert.ToInt32(ns);
 
 		Console.WriteLine(i);
 
 		foreach (String s2 in string_arr[1].Split())
 			Console.WriteLine(s2.Replace('s','z'));
 	}
 }
 

4. Reading and Writing Files

using System;
 using System.IO;
 using System.Linq;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		String my_filename = "the_file.txt";
 
 		String data = "Four score and seven years ago.";
 
 		// Write some data to the file
 		int i = 0;
 		using (FileStream fs = new FileStream(my_filename, FileMode.Create, FileAccess.Write, FileShare.None))
 		{
 			using (StreamWriter sr = new StreamWriter(fs, Encoding.GetEncoding(28591)))	// Latin-1
 			{
 				foreach (String s in data.Split())
 					sr.WriteLine((++i).ToString() + ". " + new String(s.ToCharArray().Reverse().ToArray()));
 			}
 		}
 
 		// Read data from the file
 		using (FileStream fs = File.Open(my_filename, FileMode.Open, FileAccess.Read, FileShare.Read))
 		{
 			using (StreamReader sr = new StreamReader(fs, Encoding.GetEncoding(28591)))
 			{
 				String s;
 				while (null != (s = sr.ReadLine()))
 					Console.WriteLine(s);
 			}
 		}
 	}
 }
 

5. Hash Table of User-defined Objects

using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
 public class MyObject
 {
 	public Double d_x;
 	public Double d_y;
 	public Double d_z;
 
 	// constructor
 	public MyObject(Double x_arg, Double y_arg, Double z_arg)
 	{
 		d_x = x_arg; d_y = y_arg; d_z = z_arg;
 	}
 };
 
 static class MainClass
 {
 	static void Main(String[] args)
 	{
 		Dictionary<String, MyObject> ht = new Dictionary<String, MyObject>();
 
 		ht.Add("object 1", new MyObject(3.0, 2.1, Math.PI));
 		ht.Add("object 2", new MyObject(Math.Sqrt(2.0), Math.Log(6.0,10.0), 3.2));
 		ht.Add("3rd object", new MyObject(2.1, 9.9, Double.NaN));
 
 		Console.WriteLine(ht["object 2"].d_x);
 	}
 }
 

6. LINQ Operations

One of the exciting things about mono is that it includes support for one of the latest developments in Microsoft's C# 3.5, namely Language-Integrated Query (LINQ), and its supporting technologies (extension methods and lambda expressions). LINQ allows sophisticated and concise retrieval and manipulation operations to be executed on data collections via native C# language expressions. Categories of operations include aggregation, quantification, conversion, concatenation, retrieval, set (union, intersection, etc.), generation, grouping, join, ordering, projection, partitioning, and restriction (filtering).

LINQ is an expansive topic in its own right. The following simple example gives a glimpse of what is possible.

using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
 static class MainClass
 {
 	static void Main(string[] args)
 	{
 		String[] items = { "cat", "pear", "apple", "cat", "banana", "pear", "pear", "apple" };
 
 		KeyValuePair[] tallies = items.GroupBy(k => k, e => 1)
 				.Select(f => new KeyValuePair<String, int>(f.Key.ToUpper(), f.Sum()))
 				.OrderBy(g => g.Key)
 				.ToArray();
 
 		foreach (KeyValuePair<String, int> kvp in tallies)
 			Console.WriteLine(kvp.Key + '\t' + kvp.Value);
 	}
 }
 

Result:

APPLE   2
 BANANA  1
 CAT     2
 PEAR    3
 

-- Main.gslayden - 14 Nov 2008