select_feature_set_gmmT_select_feature_set_gmmSelectFeatureSetGmmSelectFeatureSetGmm (Operator)

Name

select_feature_set_gmmT_select_feature_set_gmmSelectFeatureSetGmmSelectFeatureSetGmm — Selects an optimal combination from a set of features to classify the provided data.

Signature

Description

select_feature_set_gmmselect_feature_set_gmmSelectFeatureSetGmmSelectFeatureSetGmmSelectFeatureSetGmm selects an optimal subset from a set of features to solve a given classification problem. The classification problem has to be specified with annotated training data in ClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleclassTrainDataHandle and will be classified by a Gaussian Mixture Model. Details of the properties of this classifier can be found in create_class_gmmcreate_class_gmmCreateClassGmmCreateClassGmmCreateClassGmm.

The result of the operator is a trained classifier that is returned in GMMHandleGMMHandleGMMHandleGMMHandleGMMHandle. Additionally, the list of indices or names of the selected features is returned in SelectedFeatureIndicesSelectedFeatureIndicesSelectedFeatureIndicesSelectedFeatureIndicesselectedFeatureIndices. To use this classifier, calculate for new input data all features mentioned in SelectedFeatureIndicesSelectedFeatureIndicesSelectedFeatureIndicesSelectedFeatureIndicesselectedFeatureIndices and pass them to the classifier.

A possible application of this operator can be a comparison of different parameter sets for certain feature extraction techniques. Another application is to search for a feature that is discriminating between different classes.

To define the features that should be selected from ClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleclassTrainDataHandle, the dimensions of the feature vectors in ClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleclassTrainDataHandle can be grouped into subfeatures by calling set_feature_lengths_class_train_dataset_feature_lengths_class_train_dataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainData. A subfeature can contain several subsequent elements of a feature vector. select_feature_set_gmmselect_feature_set_gmmSelectFeatureSetGmmSelectFeatureSetGmmSelectFeatureSetGmm decides for each of these subfeatures, if it is better to use it for the classification or leave it out.

The indices of the selected subfeatures are returned in SelectedFeatureIndicesSelectedFeatureIndicesSelectedFeatureIndicesSelectedFeatureIndicesselectedFeatureIndices. If names were set in set_feature_lengths_class_train_dataset_feature_lengths_class_train_dataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainData, these names are returned instead of the indices. If set_feature_lengths_class_train_dataset_feature_lengths_class_train_dataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainData was not called for ClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleClassTrainDataHandleclassTrainDataHandle before, each element of the feature vector is considered as a subfeature.

The selection method SelectionMethodSelectionMethodSelectionMethodSelectionMethodselectionMethod is either a greedy search 'greedy'"greedy""greedy""greedy""greedy" (iteratively add the feature with highest gain) or the dynamically oscillating search 'greedy_oscillating'"greedy_oscillating""greedy_oscillating""greedy_oscillating""greedy_oscillating" (add the feature with highest gain and test then if any of the already added features can be left out without great loss). The method 'greedy'"greedy""greedy""greedy""greedy" is generally preferable, since it is faster. Only in cases when the subfeatures are low-dimensional or redundant, the method 'greedy_oscillating'"greedy_oscillating""greedy_oscillating""greedy_oscillating""greedy_oscillating" should be chosen.

The optimization criterion is the classification rate of a two-fold cross-validation of the training data. The best achieved value is returned in ScoreScoreScoreScorescore.

The following generic parameters can be set in GenParamNameGenParamNameGenParamNameGenParamNamegenParamName and GenParamValueGenParamValueGenParamValueGenParamValuegenParamValue:

'min_centers'"min_centers""min_centers""min_centers""min_centers":

Minimal number of clusters to represent a class in the training data.

Possible values: '1'"1""1""1""1", '2'"2""2""2""2"

Default value: '1'"1""1""1""1"

'max_center'"max_center""max_center""max_center""max_center":

Maximal number of clusters to represent a class in the training data.

Possible values: '1'"1""1""1""1", '5'"5""5""5""5", '10'"10""10""10""10"

Default value: '1'"1""1""1""1"

'covar_type'"covar_type""covar_type""covar_type""covar_type":

Type of the covariance to represent the size of a cluster.

Possible values: 'spherical'"spherical""spherical""spherical""spherical", 'diag'"diag""diag""diag""diag", 'full'"full""full""full""full"

Default value: 'spherical'"spherical""spherical""spherical""spherical"

'random_seed'"random_seed""random_seed""random_seed""random_seed":

Random seed.

Default value: '42'"42""42""42""42"

'threshold'"threshold""threshold""threshold""threshold":

Training threshold.

Default value: ' 0.001'" 0.001"" 0.001"" 0.001"" 0.001"

'regularize'"regularize""regularize""regularize""regularize":

Regularization value.

Default value: ' 0.0001'" 0.0001"" 0.0001"" 0.0001"" 0.0001"

'randomize'"randomize""randomize""randomize""randomize":

Randomize the input vector.

Default value: '0'"0""0""0""0"

'class_priors'"class_priors""class_priors""class_priors""class_priors":

Mode to determine the a-priori probabilities of the classes.

Possible values: 'training'"training""training""training""training", 'uniform'"uniform""uniform""uniform""uniform"

Default value: 'training'"training""training""training""training"

A more exact description of those parameters can be found in create_class_gmmcreate_class_gmmCreateClassGmmCreateClassGmmCreateClassGmm and train_class_gmmtrain_class_gmmTrainClassGmmTrainClassGmmTrainClassGmm.

Attention

This operator may take considerable time, depending on the size of the data set in the training file, and the number of features.

Please note, that this operator should not be called, if only a small set of training data is available. Due to the risk of overfitting the operator select_feature_set_gmmselect_feature_set_gmmSelectFeatureSetGmmSelectFeatureSetGmmSelectFeatureSetGmm may deliver a classifier with a very high score. However, the classifier may perfom poorly when tested.

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on internal data level.

This operator returns a handle. Note that the state of an instance of this handle type may be changed by specific operators even though the handle is used as an input parameter by those operators.

Parameters

Example (HDevelop)

* Find out which of the two features distinguishes two Classes
NameFeature1 := 'Good Feature'
NameFeature2 := 'Bad Feature'
LengthFeature1 := 3
LengthFeature2 := 2
* Create training data
create_class_train_data (LengthFeature1+LengthFeature2,\
  ClassTrainDataHandle)
* Define the features which are in the training data
set_feature_lengths_class_train_data (ClassTrainDataHandle, [LengthFeature1,\
  LengthFeature2], [NameFeature1, NameFeature2])
* Add training data
*                                                         |Feat1| |Feat2|
add_sample_class_train_data (ClassTrainDataHandle, 'row', [1,1,1,  2,1  ], 0)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [2,2,2,  2,1  ], 1)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [1,1,1,  3,4  ], 0)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [2,2,2,  3,4  ], 1)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [0,0,1,  5,6  ], 0)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [2,3,2,  5,6  ], 1)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [0,0,1,  5,6  ], 0)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [2,3,2,  5,6  ], 1)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [0,0,1,  5,6  ], 0)
add_sample_class_train_data (ClassTrainDataHandle, 'row', [2,3,2,  5,6  ], 1)
* Add more data 
* ...
* Select the better feature with a GMM
select_feature_set_gmm (ClassTrainDataHandle, 'greedy', [], [], GMMHandle,\
  SelectedFeatureGMM, Score)
* Use the classifier
* ...

Result

If the parameters are valid, the operator select_feature_set_gmmselect_feature_set_gmmSelectFeatureSetGmmSelectFeatureSetGmmSelectFeatureSetGmm returns the value 2 (H_MSG_TRUE). If necessary, an exception is raised.

Possible Predecessors

create_class_train_datacreate_class_train_dataCreateClassTrainDataCreateClassTrainDataCreateClassTrainData, add_sample_class_train_dataadd_sample_class_train_dataAddSampleClassTrainDataAddSampleClassTrainDataAddSampleClassTrainData, set_feature_lengths_class_train_dataset_feature_lengths_class_train_dataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainDataSetFeatureLengthsClassTrainData

Possible Successors

classify_class_gmmclassify_class_gmmClassifyClassGmmClassifyClassGmmClassifyClassGmm

Alternatives

select_feature_set_mlpselect_feature_set_mlpSelectFeatureSetMlpSelectFeatureSetMlpSelectFeatureSetMlp, select_feature_set_knnselect_feature_set_knnSelectFeatureSetKnnSelectFeatureSetKnnSelectFeatureSetKnn, select_feature_set_svmselect_feature_set_svmSelectFeatureSetSvmSelectFeatureSetSvmSelectFeatureSetSvm

See also

create_class_gmmcreate_class_gmmCreateClassGmmCreateClassGmmCreateClassGmm, gray_featuresgray_featuresGrayFeaturesGrayFeaturesGrayFeatures, region_featuresregion_featuresRegionFeaturesRegionFeaturesRegionFeatures

Module

Foundation