lindong28 commented on a change in pull request #54:
URL: https://github.com/apache/flink-ml/pull/54#discussion_r829628875



##########
File path: 
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/minmaxscaler/MinMaxScaler.java
##########
@@ -0,0 +1,201 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature.minmaxscaler;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.functions.RichMapPartitionFunction;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.ListStateDescriptor;
+import org.apache.flink.iteration.operator.OperatorStateUtils;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.param.Param;
+import org.apache.flink.ml.util.ParamUtils;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.runtime.state.StateInitializationContext;
+import org.apache.flink.runtime.state.StateSnapshotContext;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
+import org.apache.flink.streaming.api.operators.BoundedOneInput;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.Preconditions;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+/**
+ * An Estimator which implements the MinMaxScaler algorithm.
+ *
+ * <p>See 
https://en.wikipedia.org/wiki/Feature_scaling#Rescaling_(min-max_normalization).
+ */
+public class MinMaxScaler
+        implements Estimator<MinMaxScaler, MinMaxScalerModel>, 
MinMaxScalerParams<MinMaxScaler> {
+    private final Map<Param<?>, Object> paramMap = new HashMap<>();
+
+    public MinMaxScaler() {
+        ParamUtils.initializeMapWithDefaultValues(paramMap, this);
+    }
+
+    @Override
+    public MinMaxScalerModel fit(Table... inputs) {
+        Preconditions.checkArgument(inputs.length == 1);
+        final String featureCol = getFeaturesCol();
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
inputs[0]).getTableEnvironment();
+        DataStream<DenseVector> features =
+                tEnv.toDataStream(inputs[0])
+                        .map(
+                                (MapFunction<Row, DenseVector>)
+                                        value -> (DenseVector) 
value.getField(featureCol));
+        DataStream<DenseVector> minMaxValues =
+                features.transform(
+                                "reduceInEachPartition",
+                                features.getType(),
+                                new MinMaxReduceFunctionOperator())
+                        .transform(
+                                "reduceInFinalPartition",
+                                features.getType(),
+                                new MinMaxReduceFunctionOperator())
+                        .setParallelism(1);
+        DataStream<MinMaxScalerModelData> modelData =
+                DataStreamUtils.mapPartition(
+                        minMaxValues,
+                        new RichMapPartitionFunction<DenseVector, 
MinMaxScalerModelData>() {
+                            @Override
+                            public void mapPartition(
+                                    Iterable<DenseVector> values,
+                                    Collector<MinMaxScalerModelData> out) {
+                                Iterator<DenseVector> iter = values.iterator();
+                                DenseVector minVector = iter.next();
+                                DenseVector maxVector = iter.next();
+                                out.collect(new 
MinMaxScalerModelData(minVector, maxVector));
+                            }
+                        });
+
+        MinMaxScalerModel model =
+                new 
MinMaxScalerModel().setModelData(tEnv.fromDataStream(modelData));
+        ReadWriteUtils.updateExistingParams(model, getParamMap());
+        return model;
+    }
+
+    /**
+     * A stream operator to compute the min and max values in each partition 
of the input bounded
+     * data stream.
+     */
+    private static class MinMaxReduceFunctionOperator extends 
AbstractStreamOperator<DenseVector>
+            implements OneInputStreamOperator<DenseVector, DenseVector>, 
BoundedOneInput {
+        private ListState<DenseVector> minState;
+        private ListState<DenseVector> maxState;
+
+        private DenseVector minVector;
+        private DenseVector maxVector;
+
+        @Override
+        public void endInput() {
+            if (minVector != null) {
+                output.collect(new StreamRecord<>(minVector));
+            }
+            if (maxVector != null) {
+                output.collect(new StreamRecord<>(maxVector));
+            }
+        }
+
+        @Override
+        public void processElement(StreamRecord<DenseVector> streamRecord) {
+            DenseVector currentValue = streamRecord.getValue();
+            if (minVector == null) {
+                int vecSize = currentValue.size();
+                minVector = new DenseVector(vecSize);
+                maxVector = new DenseVector(vecSize);
+                System.arraycopy(currentValue.values, 0, minVector.values, 0, 
vecSize);
+                System.arraycopy(currentValue.values, 0, maxVector.values, 0, 
vecSize);
+
+            } else {
+                for (int i = 0; i < currentValue.size(); ++i) {

Review comment:
       Would it be useful to check that `currentValue.size() = 
maxVector.size()` here? 
   
   Maybe follow NaiveBayes.java line 256 for example.

##########
File path: 
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/minmaxscaler/MinMaxScaler.java
##########
@@ -0,0 +1,201 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature.minmaxscaler;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.functions.RichMapPartitionFunction;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.ListStateDescriptor;
+import org.apache.flink.iteration.operator.OperatorStateUtils;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.param.Param;
+import org.apache.flink.ml.util.ParamUtils;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.runtime.state.StateInitializationContext;
+import org.apache.flink.runtime.state.StateSnapshotContext;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
+import org.apache.flink.streaming.api.operators.BoundedOneInput;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.Preconditions;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+/**
+ * An Estimator which implements the MinMaxScaler algorithm.
+ *
+ * <p>See 
https://en.wikipedia.org/wiki/Feature_scaling#Rescaling_(min-max_normalization).
+ */
+public class MinMaxScaler
+        implements Estimator<MinMaxScaler, MinMaxScalerModel>, 
MinMaxScalerParams<MinMaxScaler> {
+    private final Map<Param<?>, Object> paramMap = new HashMap<>();
+
+    public MinMaxScaler() {
+        ParamUtils.initializeMapWithDefaultValues(paramMap, this);
+    }
+
+    @Override
+    public MinMaxScalerModel fit(Table... inputs) {
+        Preconditions.checkArgument(inputs.length == 1);
+        final String featureCol = getFeaturesCol();
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
inputs[0]).getTableEnvironment();
+        DataStream<DenseVector> features =
+                tEnv.toDataStream(inputs[0])
+                        .map(
+                                (MapFunction<Row, DenseVector>)
+                                        value -> (DenseVector) 
value.getField(featureCol));
+        DataStream<DenseVector> minMaxValues =
+                features.transform(
+                                "reduceInEachPartition",
+                                features.getType(),
+                                new MinMaxReduceFunctionOperator())
+                        .transform(
+                                "reduceInFinalPartition",
+                                features.getType(),
+                                new MinMaxReduceFunctionOperator())
+                        .setParallelism(1);
+        DataStream<MinMaxScalerModelData> modelData =
+                DataStreamUtils.mapPartition(
+                        minMaxValues,
+                        new RichMapPartitionFunction<DenseVector, 
MinMaxScalerModelData>() {
+                            @Override
+                            public void mapPartition(
+                                    Iterable<DenseVector> values,
+                                    Collector<MinMaxScalerModelData> out) {
+                                Iterator<DenseVector> iter = values.iterator();
+                                DenseVector minVector = iter.next();
+                                DenseVector maxVector = iter.next();
+                                out.collect(new 
MinMaxScalerModelData(minVector, maxVector));
+                            }
+                        });
+
+        MinMaxScalerModel model =
+                new 
MinMaxScalerModel().setModelData(tEnv.fromDataStream(modelData));
+        ReadWriteUtils.updateExistingParams(model, getParamMap());
+        return model;
+    }
+
+    /**
+     * A stream operator to compute the min and max values in each partition 
of the input bounded
+     * data stream.
+     */
+    private static class MinMaxReduceFunctionOperator extends 
AbstractStreamOperator<DenseVector>
+            implements OneInputStreamOperator<DenseVector, DenseVector>, 
BoundedOneInput {
+        private ListState<DenseVector> minState;
+        private ListState<DenseVector> maxState;
+
+        private DenseVector minVector;
+        private DenseVector maxVector;
+
+        @Override
+        public void endInput() {
+            if (minVector != null) {

Review comment:
       Would it be simpler to just do the following:
   ```
               if (minVector != null) {
                   output.collect(new StreamRecord<>(minVector));
                   output.collect(new StreamRecord<>(maxVector));
               }
   ```

##########
File path: 
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/minmaxscaler/MinMaxScaler.java
##########
@@ -0,0 +1,201 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature.minmaxscaler;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.functions.RichMapPartitionFunction;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.ListStateDescriptor;
+import org.apache.flink.iteration.operator.OperatorStateUtils;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.param.Param;
+import org.apache.flink.ml.util.ParamUtils;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.runtime.state.StateInitializationContext;
+import org.apache.flink.runtime.state.StateSnapshotContext;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
+import org.apache.flink.streaming.api.operators.BoundedOneInput;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.Preconditions;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+/**
+ * An Estimator which implements the MinMaxScaler algorithm.
+ *
+ * <p>See 
https://en.wikipedia.org/wiki/Feature_scaling#Rescaling_(min-max_normalization).

Review comment:
       Since the link provided here does not explain the use of min/max 
parameter, it does not exactly describe what this class does.
   
   Should we provide more detailed algorithm explanation here similar to 
Spark's MinMaxScaler Javadoc?

##########
File path: 
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/minmaxscaler/MinMaxScalerModel.java
##########
@@ -0,0 +1,181 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature.minmaxscaler;
+
+import org.apache.flink.api.common.functions.RichMapFunction;
+import org.apache.flink.api.java.typeutils.RowTypeInfo;
+import org.apache.flink.ml.api.Model;
+import org.apache.flink.ml.common.broadcast.BroadcastUtils;
+import org.apache.flink.ml.common.datastream.TableUtils;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.param.Param;
+import org.apache.flink.ml.util.ParamUtils;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.table.runtime.typeutils.ExternalTypeInfo;
+import org.apache.flink.types.Row;
+import org.apache.flink.util.Preconditions;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A Model which do a minMax scaler operation using the model data computed by 
{@link MinMaxScaler}.
+ */
+public class MinMaxScalerModel
+        implements Model<MinMaxScalerModel>, 
MinMaxScalerParams<MinMaxScalerModel> {
+    private final Map<Param<?>, Object> paramMap = new HashMap<>();
+    private Table modelDataTable;
+
+    public MinMaxScalerModel() {
+        ParamUtils.initializeMapWithDefaultValues(paramMap, this);
+    }
+
+    @Override
+    public MinMaxScalerModel setModelData(Table... inputs) {
+        modelDataTable = inputs[0];
+        return this;
+    }
+
+    @Override
+    public Table[] getModelData() {
+        return new Table[] {modelDataTable};
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public Table[] transform(Table... inputs) {
+        Preconditions.checkArgument(inputs.length == 1);
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
inputs[0]).getTableEnvironment();
+        DataStream<Row> data = tEnv.toDataStream(inputs[0]);
+        DataStream<MinMaxScalerModelData> minMaxScalerModel =
+                MinMaxScalerModelData.getModelDataStream(modelDataTable);
+        final String broadcastModelKey = "broadcastModelKey";
+        RowTypeInfo inputTypeInfo = 
TableUtils.getRowTypeInfo(inputs[0].getResolvedSchema());
+        RowTypeInfo outputTypeInfo =
+                new RowTypeInfo(
+                        ArrayUtils.addAll(
+                                inputTypeInfo.getFieldTypes(),
+                                ExternalTypeInfo.of(DenseVector.class)),
+                        ArrayUtils.addAll(inputTypeInfo.getFieldNames(), 
getPredictionCol()));
+        DataStream<Row> output =
+                BroadcastUtils.withBroadcastStream(
+                        Collections.singletonList(data),
+                        Collections.singletonMap(broadcastModelKey, 
minMaxScalerModel),
+                        inputList -> {
+                            DataStream input = inputList.get(0);
+                            return input.map(
+                                    new PredictOutputFunction(
+                                            broadcastModelKey,
+                                            getMax(),
+                                            getMin(),
+                                            getFeaturesCol()),
+                                    outputTypeInfo);
+                        });
+        return new Table[] {tEnv.fromDataStream(output)};
+    }
+
+    @Override
+    public Map<Param<?>, Object> getParamMap() {
+        return paramMap;
+    }
+
+    @Override
+    public void save(String path) throws IOException {
+        ReadWriteUtils.saveMetadata(this, path);
+        ReadWriteUtils.saveModelData(
+                MinMaxScalerModelData.getModelDataStream(modelDataTable),
+                path,
+                new MinMaxScalerModelData.ModelDataEncoder());
+    }
+
+    /**
+     * Loads model data from path.
+     *
+     * @param env Stream execution environment.
+     * @param path Model path.
+     * @return MinMaxScalerModel model.
+     */
+    public static MinMaxScalerModel load(StreamExecutionEnvironment env, 
String path)
+            throws IOException {
+        StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);
+        MinMaxScalerModel model = ReadWriteUtils.loadStageParam(path);
+        DataStream<MinMaxScalerModelData> modelData =
+                ReadWriteUtils.loadModelData(
+                        env, path, new 
MinMaxScalerModelData.ModelDataDecoder());
+        return model.setModelData(tEnv.fromDataStream(modelData));
+    }
+
+    /** This operator loads model data and predicts result. */
+    private static class PredictOutputFunction extends RichMapFunction<Row, 
Row> {
+        private final String featureCol;
+        private MinMaxScalerModelData minMaxScalerModelData;
+        private final double upperBound;
+        private final double lowerBound;
+        private final String broadcastKey;
+        private DenseVector maxVector;
+        private DenseVector minVector;
+
+        public PredictOutputFunction(
+                String broadcastKey, double upperBound, double lowerBound, 
String featureCol) {
+            this.upperBound = upperBound;
+            this.lowerBound = lowerBound;
+            this.broadcastKey = broadcastKey;
+            this.featureCol = featureCol;
+        }
+
+        @Override
+        public Row map(Row row) {
+            if (minMaxScalerModelData == null) {
+                minMaxScalerModelData =
+                        (MinMaxScalerModelData)
+                                
getRuntimeContext().getBroadcastVariable(broadcastKey).get(0);
+                maxVector = minMaxScalerModelData.maxVector;
+                minVector = minMaxScalerModelData.minVector;
+            }
+            DenseVector feature = (DenseVector) row.getField(featureCol);
+            DenseVector outputVector = new DenseVector(maxVector.size());

Review comment:
       nits: would it be simpler to rename `outputVector` as `output` for 
simplicity and consistency with `feature`?

##########
File path: 
flink-ml-lib/src/test/java/org/apache/flink/ml/feature/MinMaxScalerTest.java
##########
@@ -0,0 +1,208 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.restartstrategy.RestartStrategies;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScaler;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModel;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModelData;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vectors;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.ml.util.StageTestUtils;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import 
org.apache.flink.streaming.api.environment.ExecutionCheckpointingOptions;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.table.api.DataTypes;
+import org.apache.flink.table.api.Schema;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+
+import org.apache.commons.collections.IteratorUtils;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+/** Tests {@link MinMaxScaler} and {@link MinMaxScalerModel}. */
+public class MinMaxScalerTest {
+    @Rule public final TemporaryFolder tempFolder = new TemporaryFolder();
+    private StreamExecutionEnvironment env;
+    private StreamTableEnvironment tEnv;
+    private Table trainDataTable;
+    private Table predictDataTable;
+    private static final List<Row> trainData =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Row.of(Vectors.dense(0.0, 3.0)),
+                            Row.of(Vectors.dense(2.1, 0.0)),
+                            Row.of(Vectors.dense(4.1, 5.1)),
+                            Row.of(Vectors.dense(6.1, 8.1)),
+                            Row.of(Vectors.dense(200, 300))));
+    private static final List<Row> predictRows =
+            new 
ArrayList<>(Collections.singletonList(Row.of(Vectors.dense(150.0, 90.0))));
+
+    @Before
+    public void before() {
+        Configuration config = new Configuration();
+        
config.set(ExecutionCheckpointingOptions.ENABLE_CHECKPOINTS_AFTER_TASKS_FINISH, 
true);
+        env = StreamExecutionEnvironment.getExecutionEnvironment(config);
+        env.setParallelism(4);
+        env.enableCheckpointing(100);
+        env.setRestartStrategy(RestartStrategies.noRestart());
+        tEnv = StreamTableEnvironment.create(env);
+        Schema schema = Schema.newBuilder().column("f0", 
DataTypes.of(DenseVector.class)).build();
+        DataStream<Row> dataStream = env.fromCollection(trainData);
+        trainDataTable = tEnv.fromDataStream(dataStream, 
schema).as("features");
+        DataStream<Row> predDataStream = env.fromCollection(predictRows);
+        predictDataTable = tEnv.fromDataStream(predDataStream, 
schema).as("features");
+    }
+
+    private static void verifyPredictionResult(Table output, String outputCol, 
DenseVector expected)
+            throws Exception {
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
output).getTableEnvironment();
+        DataStream<DenseVector> stream =
+                tEnv.toDataStream(output)
+                        .map(
+                                (MapFunction<Row, DenseVector>)
+                                        row -> (DenseVector) 
row.getField(outputCol));
+        List<DenseVector> result = 
IteratorUtils.toList(stream.executeAndCollect());
+        assertEquals(1, result.size());
+        assertEquals(expected, result.get(0));
+    }
+
+    @Test
+    public void testParam() {
+        MinMaxScaler minMaxScaler = new MinMaxScaler();
+        assertEquals("features", minMaxScaler.getFeaturesCol());
+        assertEquals(1.0, minMaxScaler.getMax(), 0.0001);
+        assertEquals(0.0, minMaxScaler.getMin(), 0.0001);
+        assertEquals("prediction", minMaxScaler.getPredictionCol());
+        minMaxScaler
+                .setFeaturesCol("test_features")
+                .setMax(4.0)
+                .setMin(1.0)
+                .setPredictionCol("test_output");
+        assertEquals("test_features", minMaxScaler.getFeaturesCol());
+        assertEquals(1.0, minMaxScaler.getMin(), 0.0001);
+        assertEquals(4.0, minMaxScaler.getMax(), 0.0001);
+        assertEquals("test_output", minMaxScaler.getPredictionCol());
+    }
+
+    @Test
+    public void testFeaturePredictionParam() {
+        MinMaxScaler minMaxScaler =
+                new MinMaxScaler()
+                        .setMin(1.0)
+                        .setMax(4.0)
+                        .setFeaturesCol("test_features")
+                        .setPredictionCol("test_output");
+        MinMaxScalerModel model = 
minMaxScaler.fit(trainDataTable.as("test_features"));
+        Table output = 
model.transform(predictDataTable.as("test_features"))[0];
+        assertEquals(
+                Arrays.asList("test_features", "test_output"),
+                output.getResolvedSchema().getColumnNames());
+    }
+
+    @Test
+    public void testFewerDistinctPointsThanCluster() throws Exception {
+        MinMaxScaler minMaxScaler = new MinMaxScaler();
+        MinMaxScalerModel model = minMaxScaler.fit(predictDataTable);
+        Table result = model.transform(predictDataTable)[0];
+        verifyPredictionResult(result, minMaxScaler.getPredictionCol(), 
Vectors.dense(0.5, 0.5));
+    }
+
+    @Test
+    public void testFitAndPredict() throws Exception {
+        MinMaxScaler minMaxScaler = new MinMaxScaler();
+        MinMaxScalerModel minMaxScalerModel = minMaxScaler.fit(trainDataTable);
+        Table output = minMaxScalerModel.transform(predictDataTable)[0];
+        verifyPredictionResult(output, minMaxScaler.getPredictionCol(), 
Vectors.dense(0.75, 0.3));
+    }
+
+    @Test
+    public void testSaveLoadAndPredict() throws Exception {
+        MinMaxScaler minMaxScaler = new MinMaxScaler();
+        MinMaxScaler loadedMinMaxScaler =
+                StageTestUtils.saveAndReload(
+                        env, minMaxScaler, 
tempFolder.newFolder().getAbsolutePath());
+        MinMaxScalerModel minMaxScalerModel = 
loadedMinMaxScaler.fit(trainDataTable);
+        minMaxScalerModel =
+                StageTestUtils.saveAndReload(
+                        env, minMaxScalerModel, 
tempFolder.newFolder().getAbsolutePath());
+        assertEquals(
+                Arrays.asList("minVector", "maxVector"),
+                
minMaxScalerModel.getModelData()[0].getResolvedSchema().getColumnNames());
+        Table output = minMaxScalerModel.transform(predictDataTable)[0];
+        verifyPredictionResult(output, minMaxScaler.getPredictionCol(), 
Vectors.dense(0.75, 0.3));
+    }
+
+    @Test
+    public void testModelSaveLoadAndPredict() throws Exception {

Review comment:
       It seems that all functionalities covered in this test is already 
covered by `testSaveLoadAndPredict`. Could we remove this test for simplicity?

##########
File path: 
flink-ml-lib/src/test/java/org/apache/flink/ml/feature/MinMaxScalerTest.java
##########
@@ -0,0 +1,208 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.restartstrategy.RestartStrategies;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScaler;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModel;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModelData;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vectors;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.ml.util.StageTestUtils;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import 
org.apache.flink.streaming.api.environment.ExecutionCheckpointingOptions;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.table.api.DataTypes;
+import org.apache.flink.table.api.Schema;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+
+import org.apache.commons.collections.IteratorUtils;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+/** Tests {@link MinMaxScaler} and {@link MinMaxScalerModel}. */
+public class MinMaxScalerTest {
+    @Rule public final TemporaryFolder tempFolder = new TemporaryFolder();
+    private StreamExecutionEnvironment env;
+    private StreamTableEnvironment tEnv;
+    private Table trainDataTable;
+    private Table predictDataTable;
+    private static final List<Row> trainData =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Row.of(Vectors.dense(0.0, 3.0)),
+                            Row.of(Vectors.dense(2.1, 0.0)),
+                            Row.of(Vectors.dense(4.1, 5.1)),
+                            Row.of(Vectors.dense(6.1, 8.1)),
+                            Row.of(Vectors.dense(200, 300))));
+    private static final List<Row> predictRows =
+            new 
ArrayList<>(Collections.singletonList(Row.of(Vectors.dense(150.0, 90.0))));
+
+    @Before
+    public void before() {
+        Configuration config = new Configuration();
+        
config.set(ExecutionCheckpointingOptions.ENABLE_CHECKPOINTS_AFTER_TASKS_FINISH, 
true);
+        env = StreamExecutionEnvironment.getExecutionEnvironment(config);
+        env.setParallelism(4);
+        env.enableCheckpointing(100);
+        env.setRestartStrategy(RestartStrategies.noRestart());
+        tEnv = StreamTableEnvironment.create(env);
+        Schema schema = Schema.newBuilder().column("f0", 
DataTypes.of(DenseVector.class)).build();
+        DataStream<Row> dataStream = env.fromCollection(trainData);
+        trainDataTable = tEnv.fromDataStream(dataStream, 
schema).as("features");
+        DataStream<Row> predDataStream = env.fromCollection(predictRows);
+        predictDataTable = tEnv.fromDataStream(predDataStream, 
schema).as("features");
+    }
+
+    private static void verifyPredictionResult(Table output, String outputCol, 
DenseVector expected)
+            throws Exception {
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
output).getTableEnvironment();
+        DataStream<DenseVector> stream =
+                tEnv.toDataStream(output)
+                        .map(
+                                (MapFunction<Row, DenseVector>)
+                                        row -> (DenseVector) 
row.getField(outputCol));
+        List<DenseVector> result = 
IteratorUtils.toList(stream.executeAndCollect());
+        assertEquals(1, result.size());
+        assertEquals(expected, result.get(0));
+    }
+
+    @Test
+    public void testParam() {
+        MinMaxScaler minMaxScaler = new MinMaxScaler();
+        assertEquals("features", minMaxScaler.getFeaturesCol());
+        assertEquals(1.0, minMaxScaler.getMax(), 0.0001);
+        assertEquals(0.0, minMaxScaler.getMin(), 0.0001);
+        assertEquals("prediction", minMaxScaler.getPredictionCol());

Review comment:
       nits: could we move `prediction` to be right after "features" for a bit 
more consistency, i.e. column name features are close to each other?
   
   Same for other `assertEquals` usages and `testFeaturePredictionParam()`.

##########
File path: 
flink-ml-lib/src/test/java/org/apache/flink/ml/feature/MinMaxScalerTest.java
##########
@@ -0,0 +1,208 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.restartstrategy.RestartStrategies;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScaler;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModel;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModelData;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vectors;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.ml.util.StageTestUtils;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import 
org.apache.flink.streaming.api.environment.ExecutionCheckpointingOptions;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.table.api.DataTypes;
+import org.apache.flink.table.api.Schema;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+
+import org.apache.commons.collections.IteratorUtils;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+/** Tests {@link MinMaxScaler} and {@link MinMaxScalerModel}. */
+public class MinMaxScalerTest {
+    @Rule public final TemporaryFolder tempFolder = new TemporaryFolder();
+    private StreamExecutionEnvironment env;
+    private StreamTableEnvironment tEnv;
+    private Table trainDataTable;
+    private Table predictDataTable;
+    private static final List<Row> trainData =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Row.of(Vectors.dense(0.0, 3.0)),
+                            Row.of(Vectors.dense(2.1, 0.0)),
+                            Row.of(Vectors.dense(4.1, 5.1)),
+                            Row.of(Vectors.dense(6.1, 8.1)),
+                            Row.of(Vectors.dense(200, 300))));
+    private static final List<Row> predictRows =
+            new 
ArrayList<>(Collections.singletonList(Row.of(Vectors.dense(150.0, 90.0))));
+
+    @Before
+    public void before() {
+        Configuration config = new Configuration();
+        
config.set(ExecutionCheckpointingOptions.ENABLE_CHECKPOINTS_AFTER_TASKS_FINISH, 
true);
+        env = StreamExecutionEnvironment.getExecutionEnvironment(config);
+        env.setParallelism(4);
+        env.enableCheckpointing(100);
+        env.setRestartStrategy(RestartStrategies.noRestart());
+        tEnv = StreamTableEnvironment.create(env);
+        Schema schema = Schema.newBuilder().column("f0", 
DataTypes.of(DenseVector.class)).build();
+        DataStream<Row> dataStream = env.fromCollection(trainData);
+        trainDataTable = tEnv.fromDataStream(dataStream, 
schema).as("features");
+        DataStream<Row> predDataStream = env.fromCollection(predictRows);

Review comment:
       It appears that we don't need to explicitly create the schema. Would it 
be simpler to use the code below?
   
   ```
           trainDataTable = 
tEnv.fromDataStream(env.fromCollection(trainData)).as("features");
           predictDataTable = 
tEnv.fromDataStream(env.fromCollection(predictRows)).as("features");
   ```

##########
File path: 
flink-ml-lib/src/test/java/org/apache/flink/ml/feature/MinMaxScalerTest.java
##########
@@ -0,0 +1,208 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.feature;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.restartstrategy.RestartStrategies;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScaler;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModel;
+import org.apache.flink.ml.feature.minmaxscaler.MinMaxScalerModelData;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vectors;
+import org.apache.flink.ml.util.ReadWriteUtils;
+import org.apache.flink.ml.util.StageTestUtils;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import 
org.apache.flink.streaming.api.environment.ExecutionCheckpointingOptions;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.table.api.DataTypes;
+import org.apache.flink.table.api.Schema;
+import org.apache.flink.table.api.Table;
+import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
+import org.apache.flink.table.api.internal.TableImpl;
+import org.apache.flink.types.Row;
+
+import org.apache.commons.collections.IteratorUtils;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+/** Tests {@link MinMaxScaler} and {@link MinMaxScalerModel}. */
+public class MinMaxScalerTest {
+    @Rule public final TemporaryFolder tempFolder = new TemporaryFolder();
+    private StreamExecutionEnvironment env;
+    private StreamTableEnvironment tEnv;
+    private Table trainDataTable;
+    private Table predictDataTable;
+    private static final List<Row> trainData =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Row.of(Vectors.dense(0.0, 3.0)),
+                            Row.of(Vectors.dense(2.1, 0.0)),
+                            Row.of(Vectors.dense(4.1, 5.1)),
+                            Row.of(Vectors.dense(6.1, 8.1)),
+                            Row.of(Vectors.dense(200, 300))));
+    private static final List<Row> predictRows =

Review comment:
       Could we have multiple elements instead of just one element in the 
prediction stream? In general this could help provide more test coverage.
   
   And could we rename `predictRows` as `predictData` for consistency with 
`trainData`?




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