public static ClassifierBuildResult Create(IClassifier classifier, TextDocument[] trainingSet, string targetTag)
        {
            var errorsCount = trainingSet.Count(x => classifier.IsClassifierWrong(x, targetTag));
            var error = errorsCount * 1.0 / trainingSet.Length;

            return new ClassifierBuildResult
            {
                Classifier = classifier,
                Error = error
            };
        }