Replace Panics with error returns to BernoulliNBClassifier Fit method…

… to satisfy base.Classifier interface

naive/bernoulli_nb.go

@@ -182,22 +182,22 @@ func NewBernoulliNBClassifier() *BernoulliNBClassifier {
 
 // Fill data matrix with Bernoulli Naive Bayes model. All values
 // necessary for calculating prior probability and p(f_i)
-func (nb *BernoulliNBClassifier) Fit(X base.FixedDataGrid) {
+func (nb *BernoulliNBClassifier) Fit(X base.FixedDataGrid) error {
 
 	// Check that all Attributes are binary
 	classAttrs := X.AllClassAttributes()
 	allAttrs := X.AllAttributes()
 	featAttrs := base.AttributeDifference(allAttrs, classAttrs)
 	for i := range featAttrs {
 		if _, ok := featAttrs[i].(*base.BinaryAttribute); !ok {
-			panic(fmt.Sprintf("%v: Should be BinaryAttribute", featAttrs[i]))
+			return fmt.Errorf("%v: Should be BinaryAttribute", featAttrs[i])
 		}
 	}
 	featAttrSpecs := base.ResolveAttributes(X, featAttrs)
 
 	// Check that only one classAttribute is defined
 	if len(classAttrs) != 1 {
-		panic("Only one class Attribute can be used")
+		return fmt.Errorf("Only one class Attribute can be used")
 	}
 
 	// Number of features and instances in this training set
@@ -258,6 +258,7 @@ func (nb *BernoulliNBClassifier) Fit(X base.FixedDataGrid) {
 	}
 
 	nb.fitOn = base.NewStructuralCopy(X)
+	return nil
 }
 
 // Use trained model to predict test vector's class. The following