buildTree

private void buildTree(DecTreeNode parent,
                           List<Instance> instances,
                           List<Integer> remainingAttributes,
                           String attributeName,
                           DataSet train){

        this.labels=train.labels;
        this.attributes=train.attributes;
        this.attributeValues=train.attributeValues;
        if (attributes.isEmpty()){
            String majorLabel=pluralityValue(instances, train);
            int majorLabelIndex=labels.indexOf(majorLabel);
            parent.addChild( new DecTreeNode(majorLabelIndex, null, parent.attribute, true));
        }
        if (instances.isEmpty()){
            parent.addChild(new DecTreeNode(parent.label, null, parent.attribute, true));
        }
        else if(isPureNode(instances)){
            String pureLabel = pluralityValue(instances, train);
            int pureLabelIndex=labels.indexOf(pureLabel);
            parent.addChild(new DecTreeNode(pureLabelIndex, null, parent.attribute, true));
        }

        double entropy = calcEntropy(instances, labels.size());
        System.out.println("entropy is: "+entropy);
        int largestEntropyIndex = Integer.MIN_VALUE;
        double largestMutualInfomation = Double.MIN_VALUE;
        for (int i = 0; i < remainingAttributes.size(); i++) {
            double conditionalEntropy=calcConditionalEntropy(remainingAttributes.get(i), train);
            System.out.println("conditional entropy is: "+conditionalEntropy);
            double mutualInformation = entropy - conditionalEntropy;
            if (mutualInformation > largestMutualInfomation){
                largestMutualInfomation = mutualInformation;
                largestEntropyIndex = remainingAttributes.get(i);
            }
        }
        System.out.println("largest entropy index is: "+largestEntropyIndex);
        DecTreeNode currentNode;
        if(parent == null){
            String majorLabel = pluralityValue(instances, train);
            int majorLabelIndex=labels.indexOf(majorLabel);
            DTNode = new DecTreeNode(majorLabelIndex, largestEntropyIndex, -1 , isPureNode(instances) || remainingAttributes.size() == 1);
            currentNode = DTNode;
            parent=DTNode;
        } else {
            String majorLabel = pluralityValue(instances, train);
            int majorLabelIndex=labels.indexOf(majorLabel);
            currentNode = new DecTreeNode(majorLabelIndex, largestEntropyIndex, parent.attribute, isPureNode(instances) || remainingAttributes.size() == 0);
            parent.addChild(currentNode);
        }
        String largestEntropyAttr=attributes.get(largestEntropyIndex);
        int numBranches = attributeValues.get(largestEntropyAttr).size();
        ArrayList<ArrayList<Instance>> labelInstances = new ArrayList<ArrayList<Instance>>();
        for (int i = 0; i < numBranches; i++) {
            labelInstances.add(new ArrayList<Instance>());
        }
        for (Instance instance : instances) {
            labelInstances.get(instance.attributes.get(largestEntropyIndex)).add(instance);
        }
        for (int i = 0; i < numBranches; i++) {
            remainingAttributes.remove(remainingAttributes.indexOf(largestEntropyIndex));
            String largestEntropyAttrName=attributeValues.get(attributes.get(largestEntropyIndex)).get(i);
            buildTree(currentNode,labelInstances.get(i) , remainingAttributes, largestEntropyAttrName, train);
            remainingAttributes.add(largestEntropyIndex);
        }


    }