ITK  5.3.0
Insight Toolkit
Examples/Statistics/Subsample.cxx
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* Copyright NumFOCUS
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* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
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// Software Guide : BeginLatex
//
// \index{itk::Statistics::Subsample}
//
// The \subdoxygen{Statistics}{Subsample} is a derived sample. In other
// words, it requires another \subdoxygen{Statistics}{Sample} object for
// storing measurement vectors. The Subsample class stores a subset of
// instance identifiers from another Sample object. \emph{Any} Sample's
// subclass can be the source Sample object. You can create a Subsample
// object out of another Subsample object. The Subsample class is useful for
// storing classification results from a test Sample object or for just
// extracting some part of interest in a Sample object. Another good use of
// Subsample is sorting a Sample object. When we use an \doxygen{Image}
// object as the data source, we do not want to change the order of data
// elements in the image. However, we sometimes want to sort or
// select data elements according to their order. Statistics algorithms for
// this purpose accepts only Subsample objects as inputs. Changing the order
// in a Subsample object does not change the order of the source sample.
//
// To use a Subsample object, we include the header files for
// the class itself and a Sample class. We will use the
// \subdoxygen{Statistics}{ListSample} as the input sample.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
#include "itkListSample.h"
#include "itkSubsample.h"
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// We need another header for measurement vectors. We are going to use
// the \doxygen{Vector} class in this example.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
#include "itkVector.h"
// Software Guide : EndCodeSnippet
int
main()
{
// Software Guide : BeginLatex
//
// The following code snippet will create a ListSample object
// with three-component float measurement vectors and put three
// measurement vectors into the list.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using MeasurementVectorType = itk::Vector<float, 3>;
SampleType::Pointer sample = SampleType::New();
MeasurementVectorType mv;
mv[0] = 1.0;
mv[1] = 2.0;
mv[2] = 4.0;
sample->PushBack(mv);
mv[0] = 2.0;
mv[1] = 4.0;
mv[2] = 5.0;
sample->PushBack(mv);
mv[0] = 3.0;
mv[1] = 8.0;
mv[2] = 6.0;
sample->PushBack(mv);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// To create a Subsample instance, we define the type of the Subsample with
// the source sample type, in this case, the previously defined
// \code{SampleType}. As usual, after that, we call the \code{New()} method
// to create an instance. We must plug in the source sample, \code{sample},
// using the \code{SetSample()} method. However, with regard to data
// elements, the Subsample is empty. We specify which data elements, among
// the data elements in the Sample object, are part of the
// Subsample. There are two ways of doing that. First, if we want to
// include every data element (instance) from the sample, we simply call
// the \code{InitializeWithAllInstances()} method like the following:
//
// \small
// \begin{verbatim}
// subsample->InitializeWithAllInstances();
// \end{verbatim}
// \normalsize
//
// This method is useful when we want to create a Subsample
// object for sorting all the data elements in a Sample
// object. However, in most cases, we want to include only a subset of
// a Sample object. For this purpose, we use the
// \code{AddInstance(instance identifier)} method in this example. In
// the following code snippet, we include only the first and last
// instance in our subsample object from the three instances
// of the Sample class.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
SubsampleType::Pointer subsample = SubsampleType::New();
subsample->SetSample(sample);
subsample->AddInstance(0UL);
subsample->AddInstance(2UL);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The Subsample is ready for use. The following code snippet
// shows how to use \code{Iterator} interfaces.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
SubsampleType::Iterator iter = subsample->Begin();
while (iter != subsample->End())
{
std::cout << "instance identifier = " << iter.GetInstanceIdentifier()
<< "\t measurement vector = " << iter.GetMeasurementVector()
<< "\t frequency = " << iter.GetFrequency() << std::endl;
++iter;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// As mentioned earlier, the instances in a Subsample can be sorted without
// changing the order in the source Sample. For this purpose, the Subsample
// provides an additional instance indexing scheme. The indexing scheme is
// just like the instance identifiers for the Sample. The index is an
// integer value starting at 0, and the last value is one less than the
// number of all instances in a Subsample. The \code{Swap(0, 1)} method,
// for example, swaps two instance identifiers of the first data element
// and the second element in the Subsample. Internally, the \code{Swap()}
// method changes the instance identifiers in the first and second
// position. Using indices, we can print out the effects of the
// \code{Swap()} method. We use the
// \code{GetMeasurementVectorByIndex(index)} to get the measurement vector
// at the index position. However, if we want to use the common methods of
// Sample that accepts instance identifiers, we call them after we get
// the instance identifiers using \code{GetInstanceIdentifier(index)}
// method.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
subsample->Swap(0, 1);
for (int index = 0; index < subsample->Size(); ++index)
{
std::cout << "instance identifier = "
<< subsample->GetInstanceIdentifier(index)
<< "\t measurement vector = "
<< subsample->GetMeasurementVectorByIndex(index) << std::endl;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Since we are using a ListSample object as the source sample, the
// following code snippet will return the same value (2) for the
// \code{Size()} and the \code{GetTotalFrequency()} methods. However, if we
// used a Histogram object as the source sample, the two return
// values might be different because a Histogram allows varying
// frequency values for each instance.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
std::cout << "Size = " << subsample->Size() << std::endl;
std::cout << "Total frequency = " << subsample->GetTotalFrequency()
<< std::endl;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// If we want to remove all instances that are associated with the
// Subsample, we call the \code{Clear()} method. After this invocation, the
// \code{Size()} and the \code{GetTotalFrequency()} methods return 0.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
subsample->Clear();
std::cout << "Size = " << subsample->Size() << std::endl;
std::cout << "Total frequency = " << subsample->GetTotalFrequency()
<< std::endl;
// Software Guide : EndCodeSnippet
return EXIT_SUCCESS;
}
itkSubsample.h
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
itk::Statistics::Subsample
This class stores a subset of instance identifiers from another sample object. You can create a subsa...
Definition: itkSubsample.h:42
itkListSample.h
itkVector.h