button near the top of the Classify tab. A dialog window appears showing various
types of classifier. Click the trees entry to reveal its subentries, and click J48 to choose
that classifier. Classifiers, like filters, are organized in a hierarchy: J48 has the full
name weka.classifiers.trees.J48.
The classifier is shown in the text box next to the Choose button: It now reads
J48 –C 0.25 –M 2. This text gives the default parameter settings for this classifier,
which in this case rarely require changing to obtain good performance.
For illustrative purposes we evaluate the performance using the training data,
which has been loaded in the Preprocess panel—this is not generally a good idea
because it leads to unrealistically optimistic performance estimates. Choose Use
training set from the Test options part of the Classify panel. Once the test strategy
has been set, the classifier is built and evaluated by pressing the Start button.
This processes the training set using the currently selected learning algorithm,
C4.5 in this case. Then it classifies all the instances in the training data and
outputs performance statistics. These are shown in Figure 17.2(a).
button near the top of the Classify tab. A dialog window appears showing various
types of classifier. Click the trees entry to reveal its subentries, and click J48 to choose
that classifier. Classifiers, like filters, are organized in a hierarchy: J48 has the full
name weka.classifiers.trees.J48.
The classifier is shown in the text box next to the Choose button: It now reads
J48 –C 0.25 –M 2. This text gives the default parameter settings for this classifier,
which in this case rarely require changing to obtain good performance.
For illustrative purposes we evaluate the performance using the training data,
which has been loaded in the Preprocess panel—this is not generally a good idea
because it leads to unrealistically optimistic performance estimates. Choose Use
training set from the Test options part of the Classify panel. Once the test strategy
has been set, the classifier is built and evaluated by pressing the Start button.
This processes the training set using the currently selected learning algorithm,
C4.5 in this case. Then it classifies all the instances in the training data and
outputs performance statistics. These are shown in Figure 17.2(a).
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