find exact numbers of true postive in weka - matlab

Question

In WEKA, I can easily find the TP Rate and total True Classified Instances from Confusion Matrix but is there any way to see exact number of tp and/or tn?
And do you know any way to find these values in matlab-anfis?

Answer 1

Since you are mentioning MATLAB, I'm assuming you are using the Java API to the Weka library to programmatically build classifiers.
In that case, you can evaluate the model using the weka.classifiers.Evaluation class, which provides all sorts of statistics.
Assuming you already have weka.jar file on the java class path (see javaaddpath function), here is an example in MATLAB:
%# data
fName = 'C:\Program Files\Weka-3-7\data\iris.arff';
loader = weka.core.converters.ArffLoader();
loader.setFile( java.io.File(fName) );
data = loader.getDataSet();
data.setClassIndex( data.numAttributes()-1 );
%# classifier
classifier = weka.classifiers.trees.J48();
classifier.setOptions( weka.core.Utils.splitOptions('-C 0.25 -M 2') );
classifier.buildClassifier( data );
%# evaluation
evl = weka.classifiers.Evaluation(data);
pred = evl.evaluateModel(classifier, data, {''});
%# display
disp(classifier.toString())
disp(evl.toSummaryString())
disp(evl.toClassDetailsString())
disp(evl.toMatrixString())
%# confusion matrix and other stats
cm = evl.confusionMatrix();
%# number of TP/TN/FP/FN with respect to class=1 (Iris-versicolor)
tp = evl.numTruePositives(1);
tn = evl.numTrueNegatives(1);
fp = evl.numFalsePositives(1);
fn = evl.numFalseNegatives(1);
%# class=XX is a zero-based index which maps to the following class values
classValues = arrayfun(#(k)char(data.classAttribute.value(k-1)), ...
1:data.classAttribute.numValues, 'Uniform',false);
The output:
J48 pruned tree
------------------
petalwidth <= 0.6: Iris-setosa (50.0)
petalwidth > 0.6
| petalwidth <= 1.7
| | petallength <= 4.9: Iris-versicolor (48.0/1.0)
| | petallength > 4.9
| | | petalwidth <= 1.5: Iris-virginica (3.0)
| | | petalwidth > 1.5: Iris-versicolor (3.0/1.0)
| petalwidth > 1.7: Iris-virginica (46.0/1.0)
Number of Leaves : 5
Size of the tree : 9
Correctly Classified Instances 147 98 %
Incorrectly Classified Instances 3 2 %
Kappa statistic 0.97
Mean absolute error 0.0233
Root mean squared error 0.108
Relative absolute error 5.2482 %
Root relative squared error 22.9089 %
Coverage of cases (0.95 level) 98.6667 %
Mean rel. region size (0.95 level) 34 %
Total Number of Instances 150
=== Detailed Accuracy By Class ===
TP Rate FP Rate Precision Recall F-Measure MCC ROC Area PRC Area Class
1.000 0.000 1.000 1.000 1.000 1.000 1.000 1.000 Iris-setosa
0.980 0.020 0.961 0.961 0.961 0.955 0.990 0.969 Iris-versicolor
0.960 0.010 0.980 0.980 0.980 0.955 0.990 0.970 Iris-virginica
Weighted Avg. 0.980 0.010 0.980 0.980 0.980 0.970 0.993 0.980
=== Confusion Matrix ===
a b c <-- classified as
50 0 0 | a = Iris-setosa
0 49 1 | b = Iris-versicolor
0 2 48 | c = Iris-virginica