ITK  5.3.0
Insight Toolkit
Examples/Statistics/ListSample.cxx
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* Copyright NumFOCUS
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* Licensed under the Apache License, Version 2.0 (the "License");
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// Software Guide : BeginLatex
//
// This example illustrates the common interface of the \code{Sample} class
// in Insight.
//
// \index{itk::Sample!Interfaces}
// \index{itk::Statistics::ListSample}
//
// Different subclasses of \subdoxygen{Statistics}{Sample} expect different
// sets of template arguments. In this example, we use the
// \subdoxygen{Statistics}{ListSample} class that requires the type of
// measurement vectors. The ListSample uses
// \href{http://www.sgi.com/tech/stl/}{STL} \code{vector} to store
// measurement vectors. This class conforms to the common interface of Sample.
// Most methods of the Sample class interface are for retrieving measurement
// vectors, the size of a container, and the total frequency. In this
// example, we will see those information retrieving methods in addition to
// methods specific to the ListSample class for data input.
//
// To use the ListSample class, we include the header file for the class.
//
// We need another header for measurement vectors. We are going to use
// the \doxygen{Vector} class which is a subclass of the \doxygen{FixedArray}
// class.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
#include "itkListSample.h"
#include "itkVector.h"
// Software Guide : EndCodeSnippet
int
main()
{
// Software Guide : BeginLatex
//
// The following code snippet defines the measurement vector type as a
// three component \code{float} \doxygen{Vector}. The
// \code{MeasurementVectorType} is the measurement vector type in the
// \code{SampleType}. An object is instantiated at the third line.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using MeasurementVectorType = itk::Vector<float, 3>;
SampleType::Pointer sample = SampleType::New();
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// In the above code snippet, the namespace
// specifier for ListSample is \code{itk::Statistics::} instead of the
// usual namespace specifier for other ITK classes, \code{itk::}.
//
// The newly instantiated object does not have any data in it. We
// have two different ways of storing data elements. The first method
// is using the \code{PushBack} method.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
MeasurementVectorType mv;
mv[0] = 1.0;
mv[1] = 2.0;
mv[2] = 4.0;
sample->PushBack(mv);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The previous code increases the size of the container by one and
// stores \code{mv} as the first data element in it.
//
// The other way to store data elements is calling the \code{Resize} method
// and then calling the \code{SetMeasurementVector()} method with a
// measurement vector. The following code snippet increases the size of the
// container to three and stores two measurement vectors at the second and
// the third slot. The measurement vector stored using the \code{PushBack}
// method above is still at the first slot.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
sample->Resize(3);
mv[0] = 2.0;
mv[1] = 4.0;
mv[2] = 5.0;
sample->SetMeasurementVector(1, mv);
mv[0] = 3.0;
mv[1] = 8.0;
mv[2] = 6.0;
sample->SetMeasurementVector(2, mv);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// We have seen how to create an ListSample object and store
// measurement vectors using the ListSample-specific interface. The
// following code shows the common interface of the Sample class. The
// \code{Size} method returns the number of measurement vectors in the
// sample. The primary data stored in Sample subclasses are measurement
// vectors. However, each measurement vector has its associated frequency
// of occurrence within the sample. For the
// ListSample and the adaptor classes (see Section
// \ref{sec:SampleAdaptors}), the frequency value is always one.
// \subdoxygen{Statistics}{Histogram} can have a varying frequency
// (\code{float} type) for each measurement vector. We retrieve measurement
// vectors using the \code{GetMeasurementVector(unsigned long instance
// identifier)}, and frequency using the \code{GetFrequency(unsigned long
// instance identifier)}.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
for (unsigned long i = 0; i < sample->Size(); ++i)
{
std::cout << "id = " << i
<< "\t measurement vector = " << sample->GetMeasurementVector(i)
<< "\t frequency = " << sample->GetFrequency(i) << std::endl;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The output should look like the following:\newline
// \code{id = 0 measurement vector = 1 2 4 frequency = 1}\newline
// \code{id = 1 measurement vector = 2 4 5 frequency = 1}\newline
// \code{id = 2 measurement vector = 3 8 6 frequency = 1}\newline
//
// We can get the same result with its iterator.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
SampleType::Iterator iter = sample->Begin();
while (iter != sample->End())
{
std::cout << "id = " << iter.GetInstanceIdentifier()
<< "\t measurement vector = " << iter.GetMeasurementVector()
<< "\t frequency = " << iter.GetFrequency() << std::endl;
++iter;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The last method defined in the Sample class
// is the \code{GetTotalFrequency()} method that returns the sum of
// frequency values associated with every measurement vector in a
// container. In the case of ListSample and the
// adaptor classes, the return value should be exactly the same as that of
// the \code{Size()} method, because the frequency values are always one
// for each measurement vector. However, for the
// \subdoxygen{Statistics}{Histogram}, the frequency values can vary.
// Therefore, if we want to develop a general algorithm to calculate the
// sample mean, we must use the \code{GetTotalFrequency()} method instead of
// the \code{Size()} method.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
std::cout << "Size = " << sample->Size() << std::endl;
std::cout << "Total frequency = " << sample->GetTotalFrequency()
<< std::endl;
// Software Guide : EndCodeSnippet
return EXIT_SUCCESS;
}
itk::Vector
A templated class holding a n-Dimensional vector.
Definition: itkVector.h:62
itk::Statistics::ListSample
This class is the native implementation of the a Sample with an STL container.
Definition: itkListSample.h:51
itkListSample.h
itkVector.h