Easy way of finding centriod using octave

Octave code:
A=[10 11; 20 21; 30 31; 40 41; 50 51; 60 61; 70 71]
PB = [1 1 3 3 2 2 2]

C = A (PB==3,:)
D = mean(C)
SD = size(C,1)

Results:
A =

   10   11
   20   21
   30   31
   40   41
   50   51
   60   61
   70   71

PB =

   1   1   3   3   2   2   2

C =

   30   31
   40   41

D =

   35   36

SD =  2

Simplified code:

for i=1:K
    centroids(i,:) = mean( X(idx==i,:) );
endfor

Array indexing in Octave

A=[10 11; 20 21; 30 31; 40 41; 60 61; 60 61; 70 71]
PB = [1 3 5]
B = [1 2 3 4 7]
C = A (B(PB),:)
D = mean(C)

A =

   10   11
   20   21
   30   31
   40   41
   60   61
   60   61
   70   71

PB =

   1   3   5

B =

   1   2   3   4   7

C =

   10   11
   30   31
   70   71

D =

   36.667   37.667

WPF update user interface in multithreading mode

   public partial class Window1 : Window  
   {  
     public Class1 c;  
     public Window1()  
     {  
       InitializeComponent();  
       c = new Class1();  
       c.Class1Event += C_Class1Event;  
      }  
     private void C_Class1Event(object sender, Class1EventArgs e)  
     {//Triggered from a different thread  

       this.Dispatcher.Invoke((Action)(() =>  
       {//this refer to form in WPF application   
         imgShirt.Source = new BitmapImage(new Uri(System.AppDomain.CurrentDomain.BaseDirectory + @"\images2.jpg", UriKind.RelativeOrAbsolute));  
       }));  

     }  
     private void Change_Click(object sender, RoutedEventArgs e)  
     {  
       c.Start();  
     }  
     private void Change2_Click(object sender, RoutedEventArgs e)  
     {//Called from the same thread  
       Uri fileUri = new Uri(System.AppDomain.CurrentDomain.BaseDirectory + @"\images.jpg", UriKind.RelativeOrAbsolute);  
       imgShirt.Source = new BitmapImage(fileUri);  
     }  
   }  

   public class Class1  
   {  
     public event EventHandler<Class1EventArgs> Class1Event;  
     public Class1()  
     {  
     }  
     public void Start()  
     {  
       Task.Run(() => {  
         Class1EventArgs e = new Class1EventArgs();  
         Class1Event(this, e);  
       });  
     }  
   }  
   public class Class1EventArgs : EventArgs  
   {  
   }  

How to deserialize Xml with different namespaces / prefixes

Specify the namespace in the child element

 [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "4.8.3928.0")]  
 [System.SerializableAttribute()]  
 [System.Diagnostics.DebuggerStepThroughAttribute()]  
 [System.ComponentModel.DesignerCategoryAttribute("code")]  
 [System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]  
 [System.Xml.Serialization.XmlRootAttribute(Namespace= "http://search.yahoo.com/mrss/", IsNullable=false)]  
 public partial class group {  
   private groupContent[] contentField;  
   /// <remarks/>  
   [System.Xml.Serialization.XmlElementAttribute("content")]  
   public groupContent[] content {  
     get {  
       return this.contentField;  
     }  
     set {  
       this.contentField = value;  
     }  
   }  
 }  

Use the XmlElement tag and specify the namespace in the parent node

   /// <remarks/>  
   public string pubDate {  
     get {  
       return this.pubDateField;  
     }  
     set {  
       this.pubDateField = value;  
     }  
   }  
   [XmlElement("group", Namespace = "http://search.yahoo.com/mrss/")]  
   public group group  
   {  
     get  
     {  
       return this.groupField;  
     }  
     set  
     {  
       this.groupField = value;  
     }  
   }  
 }  

Note: If you want to use the Visual Studio xsd.exe to generate the C# class, you need to strip off the elements with different namespace for xsd.exe to work. You can add the separate elements manually after.

C++ Use Boost property_tree to manipulate xml files

#include "pch.h"
#include <iostream>
#include <string>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>

using namespace std;
int main()
{
 string path = "C:\\Work\\Students.xml";
 string path2 = "C:\\Work\\Students2.xml";
 try
 {
  std::cout << "Using property tree to manipulate XML files\n";
  //how to load an xml file
  boost::property_tree::ptree pt;
  read_xml(path, pt);

  boost::property_tree::ptree& Students = pt.get_child("Students");

  //how to remove a node using Id
  for (auto it = Students.begin(); it != Students.end();)
  {
   int id = it->second.get(".Id");
   if (id == 1)
   {
    it = Students.erase(it);
    
   }
   else
   {
    ++it;
   }
  }
  //how to add nodes
  for (auto data : { 3, 4, 5 })
  {
   boost::property_tree::ptree& Student = Students.add("Student", "");
   Student.add(".Id", data);
   Student.add("LastName", "McDonalds");
   Student.add("FirstName", "Robert");
  }

  //how to save
  write_xml(path2, pt, std::locale(), boost::property_tree::xml_writer_make_settings('\t', 1));

 }
 catch (exception e)
 {
  string s = e.what();
  std::cout << s;
 }
}

SWIG, pass C++ array of classes back to C# example

Step 1 Create a C++ Windows DLL Project StudentDll

Step 2 Add Student.h file

#pragma once
#include
#include
class Student
{
public:
std::string FirstName;
std::string LastName;
Student(std::string _FirstName, std::string _LastName);
Student();
};

std::vector GetStudents();

Step 3 Add Student.cpp file

#include "stdafx.h"

#include "Student.h"

Student::Student(std::string _FirstName, std::string _LastName)

{

FirstName = _FirstName;

LastName = _LastName;

}

Student::Student()

{

}

std::vector GetStudents()

{

std::vector sv;

sv.push_back(Student("John", "Smith"));

sv.push_back(Student("Mary", "Boyle"));

return sv;

}

Step 4 Add Student.i file

%module StudentDll
%include "std_string.i"

%apply const std::string& {std::string* FirstName};
%apply const std::string& {std::string* LastName};
%{
#include "student.h"
%}

%include

%include "student.h"

Step 4a

Select Student.i, Properties, General, Item Type as Custom Build Tool.

Select Apply to create the Custom Build Tool property group.

In Custom Build Tool, General, Command Line enter:
swig -csharp -c++ -outdir  Student.i

In Outputs, enter Student_wrap.cxx, and click OK to close the dialog.

Right-click Student.i and Compile. This should create four files: three in the C# Generated folder and one in the C++ project.

Create a Generated Files filter in the C++ project and add Student_wrap.cxx to it.

Step 5 Add StudentVector.i file

%module StudentVectorDll

%include std_vector.i
%include std_string.i

/* allow partial c# classes */
%typemap(csclassmodifiers) SWIGTYPE "public partial class"

/* generate template around vector */

%template(StudentVector) std::vector;


Step 5a

Select Student.i, Properties, General, Item Type as Custom Build Tool.

Select Apply to create the Custom Build Tool property group.

In Custom Build Tool, General, Command Line enter:
swig -csharp -c++ -outdir GeneratedFolderPath StudentVector.i

In Outputs, enter StudentVector_wrap.cxx, and click OK to close the dialog.

Right-click StudentVector.i and Compile. This should create four files: three in the C# Generated folder and one in the C++ project.

Create a Generated Files filter in the C++ project and add StudentVector_wrap.cxx to it.

Step 6 Create a C# .Net Framework project StudentConsumer

Fill in the default Program.cs file as follow

using System.Text;
using System.Threading.Tasks;

namespace StudentConsumer
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World");
            var s = StudentDllPINVOKE.GetStudents();
            StudentVector sv = new StudentVector(s, true);
            var sv0 = sv[0];
            var sv00 = SWIGTYPE_p_Student.getCPtr(sv0);
            var sv01 = new Student(sv00);
            Console.WriteLine(sv01.FirstName + ", " + sv01.LastName);

            Console.ReadKey();
        }
    }

}

Step 7 Add Generated folder in the C# Student Consumer project

Step 7a Add the content of GeneratedFolderPath folder from C++ StudentDll project to the Generated folder

Step 7b Add an extra Constructor in the Student.cs

public class Student : global::System.IDisposable {
  private global::System.Runtime.InteropServices.HandleRef swigCPtr;
  protected bool swigCMemOwn;

  public Student(global::System.Runtime.InteropServices.HandleRef _swigCPtr)
    {
        swigCPtr = _swigCPtr;
    }

Step 8 Set the StartUp project as StudentConsumer and Run it

swig is a good tool for converting interpolating code between C++ and other languages
http://www.swig.org/

C++ how using reserve method in vector reduces the number of times copy constructor is called

 #include "stdafx.h"  
 #include <iostream>  
 #include <vector>  
 #include <queue>  
 #include <ctime>  
 #include <chrono>  
 #include <type_traits>  
 #include <string>  
 #include <fstream>  
 using namespace std;  
 using namespace std::chrono;  
 class Point  
 {  
 public:  
      int x; int y;  
      Point(int _x, int _y)  
      {  
           x = _x;  
           y = _y;  
           cout << "constructor " << x << ", " << y << endl;  
      }  
      ~Point()  
      {  
           cout << "destructor " << x << ", " << y <<endl;  
      }  
      Point(const Point& p)  
      {  
           x = p.x;  
           y = p.y;  
           cout << "!!! copy constructor " << x << ", " << y << endl;  
      }  
      friend std::ostream& operator<< (std::ostream& stream, const Point& p) {  
           return stream << "(" << p.x << ", " << p.y << ")";  
      }  
 };  
 Point CreatePoint()  
 {  
      Point p(100, 101);  
      return p;  
 }  
 int main()  
 {  
      vector<Point> p;  
      p.push_back(Point(1, 2));  
      p.push_back(Point(3, 4));  
      p.push_back(Point(5, 6));  
      vector<Point> p2;  
      p2.reserve(3);  
      p2.push_back(Point(10, 20));  
      p2.push_back(Point(30, 40));  
      p2.push_back(Point(50, 60));  
      Point cp = CreatePoint();  
      cout << "tesing completed." << endl;  
      getchar();  
   return 0;  
 }  

Output

constructor 1, 2
!!! copy constructor 1, 2
destructor 1, 2
constructor 3, 4
!!! copy constructor 3, 4
!!! copy constructor 1, 2
destructor 1, 2
destructor 3, 4
constructor 5, 6
!!! copy constructor 5, 6
!!! copy constructor 1, 2
!!! copy constructor 3, 4
destructor 1, 2
destructor 3, 4
destructor 5, 6
constructor 10, 20
!!! copy constructor 10, 20
destructor 10, 20
constructor 30, 40
!!! copy constructor 30, 40
destructor 30, 40
constructor 50, 60
!!! copy constructor 50, 60
destructor 50, 60
constructor 100, 101
tesing completed.
destructor 100, 101
destructor 10, 20
destructor 30, 40
destructor 50, 60
destructor 1, 2
destructor 3, 4
destructor 5, 6