Added support for the 'StringLengthTransformer' transformation type

Author: vruusmann

README.md

@@ -444,6 +444,7 @@ Java library and command-line application for converting [Scikit-Learn](https://
     * `sklearn2pmml.preprocessing.SecondsSinceYearTransformer`
     * `sklearn2pmml.preprocessing.SelectFirstTransformer`
     * `sklearn2pmml.preprocessing.SeriesConstructor`
+    * `sklearn2pmml.preprocessing.StringLengthTransformer`
     * `sklearn2pmml.preprocessing.StringNormalizer`
     * `sklearn2pmml.preprocessing.SubstringTransformer`
     * `sklearn2pmml.preprocessing.WordCountTransformer`

pmml-sklearn/src/main/java/sklearn2pmml/preprocessing/StringLengthTransformer.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2025 Villu Ruusmann
+ *
+ * This file is part of JPMML-SkLearn
+ *
+ * JPMML-SkLearn is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * JPMML-SkLearn is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with JPMML-SkLearn.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package sklearn2pmml.preprocessing;
+
+import java.util.Collections;
+import java.util.List;
+
+import org.dmg.pmml.Apply;
+import org.dmg.pmml.DataType;
+import org.dmg.pmml.DerivedField;
+import org.dmg.pmml.OpType;
+import org.dmg.pmml.PMMLFunctions;
+import org.jpmml.converter.ContinuousFeature;
+import org.jpmml.converter.ExpressionUtil;
+import org.jpmml.converter.Feature;
+import org.jpmml.python.ClassDictUtil;
+import org.jpmml.sklearn.SkLearnEncoder;
+
+public class StringLengthTransformer extends StringTransformer {
+
+	public StringLengthTransformer(String module, String name){
+		super(module, name);
+	}
+
+	@Override
+	public List<Feature> encodeFeatures(List<Feature> features, SkLearnEncoder encoder){
+		ClassDictUtil.checkSize(1, features);
+
+		Feature feature = features.get(0);
+
+		Apply apply = ExpressionUtil.createApply(PMMLFunctions.STRINGLENGTH, feature.ref());
+
+		DerivedField derivedField = encoder.createDerivedField(createFieldName("length", feature), OpType.CONTINUOUS, DataType.INTEGER, apply);
+
+		return Collections.singletonList(new ContinuousFeature(encoder, derivedField));
+	}
+}

pmml-sklearn/src/main/resources/META-INF/sklearn2pmml.properties

@@ -219,6 +219,7 @@ sklearn2pmml.preprocessing.SecondsSinceMidnightTransformer =
 sklearn2pmml.preprocessing.SecondsSinceYearTransformer =
 sklearn2pmml.preprocessing.SelectFirstTransformer =
 sklearn2pmml.preprocessing.SeriesConstructor =
+sklearn2pmml.preprocessing.StringLengthTransformer =
 sklearn2pmml.preprocessing.StringNormalizer =
 sklearn2pmml.preprocessing.SubstringTransformer =
 sklearn2pmml.preprocessing.WordCountTransformer =