presto-ml/src/main/java/io/prestosql/plugin/ml/MLFunctions.java/MLFunctions/varcharClassify
class MLFunctions:    @ScalarFunction("classify")
    @SqlType(StandardTypes.VARCHAR)
    public static Slice varcharClassify(@SqlType(MAP_BIGINT_DOUBLE) Block featuresMap, @SqlType("Classifier(varchar)") Slice modelSlice)
    {
        FeatureVector features = ModelUtils.toFeatures(featuresMap);
        Model model = getOrLoadModel(modelSlice);
        checkArgument(model.getType().equals(VARCHAR_CLASSIFIER), "model is not a Classifier(varchar)");
        Classifier<String> varcharClassifier = (Classifier<String>) model;
        return Slices.utf8Slice(varcharClassifier.classify(features));
    }