yunfengzhou-hub commented on code in PR #172:
URL: https://github.com/apache/flink-ml/pull/172#discussion_r1017456006


##########
flink-ml-lib/src/main/java/org/apache/flink/ml/common/param/HasRelativeError.java:
##########
@@ -36,7 +36,7 @@ default double getRelativeError() {
         return get(RELATIVE_ERROR);
     }
 
-    default T setFeaturesCol(double value) {
+    default T setRelativeError(double value) {

Review Comment:
   Let's add tests for `setRelativeError` and `getRelativeError` in 
`ImputerTest.testParams`.



##########
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/robustscaler/RobustScaler.java:
##########
@@ -0,0 +1,183 @@
+/*
+ * 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.robustscaler;
+
+import org.apache.flink.api.common.functions.AggregateFunction;
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.common.util.QuantileSummary;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vector;
+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.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.Preconditions;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Scale features using statistics that are robust to outliers.

Review Comment:
   Let's make the JavaDoc begin with a noun or definition. For example,
   - An algorithm that scales xxx
   - RobustScaler is an algorithm that scales xxx



##########
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/robustscaler/RobustScaler.java:
##########
@@ -0,0 +1,183 @@
+/*
+ * 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.robustscaler;
+
+import org.apache.flink.api.common.functions.AggregateFunction;
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.common.util.QuantileSummary;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vector;
+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.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.Preconditions;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Scale features using statistics that are robust to outliers.
+ *
+ * <p>This Scaler removes the median and scales the data according to the 
quantile range (defaults
+ * to IQR: Interquartile Range). The IQR is the range between the 1st quartile 
(25th quantile) and
+ * the 3rd quartile (75th quantile) but can be configured.
+ *
+ * <p>Centering and scaling happen independently on each feature by computing 
the relevant
+ * statistics on the samples in the training set. Median and quantile range 
are then stored to be
+ * used on later data using the transform method.
+ *
+ * <p>Standardization of a dataset is a common requirement for many machine 
learning estimators.
+ * Typically this is done by removing the mean and scaling to unit variance. 
However, outliers can
+ * often influence the sample mean / variance in a negative way. In such 
cases, the median and the
+ * interquartile range often give better results.
+ */
+public class RobustScaler
+        implements Estimator<RobustScaler, RobustScalerModel>, 
RobustScalerParams<RobustScaler> {
+    private final Map<Param<?>, Object> paramMap = new HashMap<>();
+
+    public RobustScaler() {
+        ParamUtils.initializeMapWithDefaultValues(paramMap, this);
+    }
+
+    @Override
+    public RobustScalerModel fit(Table... inputs) {
+        Preconditions.checkArgument(inputs.length == 1);
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
inputs[0]).getTableEnvironment();
+        DataStream<DenseVector> inputData =
+                tEnv.toDataStream(inputs[0])
+                        .map(
+                                (MapFunction<Row, DenseVector>)
+                                        value ->
+                                                ((Vector) 
value.getField(getInputCol())).toDense());
+        DataStream<RobustScalerModelData> modelData =
+                DataStreamUtils.aggregate(
+                        inputData,
+                        new QuantileAggregator(getRelativeError(), getLower(), 
getUpper()));
+        RobustScalerModel model =
+                new 
RobustScalerModel().setModelData(tEnv.fromDataStream(modelData));
+        ReadWriteUtils.updateExistingParams(model, getParamMap());
+        return model;
+    }
+
+    /**
+     * A stream operator to compute the medians and quantile ranges from 
feature column of the input

Review Comment:
   It might be better to change "stream operator" to "function" or "aggregate 
function".



##########
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/robustscaler/RobustScalerModel.java:
##########
@@ -0,0 +1,179 @@
+/*
+ * 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.robustscaler;
+
+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.BLAS;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vector;
+import org.apache.flink.ml.linalg.typeinfo.VectorTypeInfo;
+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.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.Preconditions;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/** A Model which transforms data using the model data computed by {@link 
RobustScaler}. */
+public class RobustScalerModel
+        implements Model<RobustScalerModel>, 
RobustScalerModelParams<RobustScalerModel> {
+
+    private final Map<Param<?>, Object> paramMap = new HashMap<>();
+    private Table modelDataTable;
+
+    public RobustScalerModel() {
+        ParamUtils.initializeMapWithDefaultValues(paramMap, this);
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public Table[] transform(Table... inputs) {
+        Preconditions.checkArgument(inputs.length == 1);
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
inputs[0]).getTableEnvironment();
+        DataStream<Row> inputStream = tEnv.toDataStream(inputs[0]);
+
+        RowTypeInfo inputTypeInfo = 
TableUtils.getRowTypeInfo(inputs[0].getResolvedSchema());
+        RowTypeInfo outputTypeInfo =
+                new RowTypeInfo(
+                        ArrayUtils.addAll(inputTypeInfo.getFieldTypes(), 
VectorTypeInfo.INSTANCE),
+                        ArrayUtils.addAll(inputTypeInfo.getFieldNames(), 
getOutputCol()));
+        final String broadcastModelKey = "broadcastModelKey";
+        DataStream<RobustScalerModelData> modelDataStream =
+                RobustScalerModelData.getModelDataStream(modelDataTable);
+
+        DataStream<Row> output =
+                BroadcastUtils.withBroadcastStream(
+                        Collections.singletonList(inputStream),
+                        Collections.singletonMap(broadcastModelKey, 
modelDataStream),
+                        inputList -> {
+                            DataStream inputData = inputList.get(0);
+                            return inputData.map(
+                                    new PredictOutputFunction(
+                                            broadcastModelKey,
+                                            getInputCol(),
+                                            getWithCentering(),
+                                            getWithScaling()),
+                                    outputTypeInfo);
+                        });
+
+        return new Table[] {tEnv.fromDataStream(output)};
+    }
+
+    /** This operator loads model data and predicts result. */
+    private static class PredictOutputFunction extends RichMapFunction<Row, 
Row> {
+        private final String broadcastModelKey;
+        private final String inputCol;
+        private final boolean withCentering;
+        private final boolean withScaling;
+
+        private DenseVector medians;
+        private DenseVector scales;
+
+        public PredictOutputFunction(
+                String broadcastModelKey,
+                String inputCol,
+                boolean withCentering,
+                boolean withScaling) {
+            this.broadcastModelKey = broadcastModelKey;
+            this.inputCol = inputCol;
+            this.withCentering = withCentering;
+            this.withScaling = withScaling;
+        }
+
+        @Override
+        public Row map(Row row) throws Exception {
+            if (medians == null) {
+                RobustScalerModelData modelData =
+                        (RobustScalerModelData)
+                                
getRuntimeContext().getBroadcastVariable(broadcastModelKey).get(0);
+                medians = modelData.medians;
+                scales =
+                        new DenseVector(
+                                Arrays.stream(modelData.ranges.values)
+                                        .map(range -> range == 0 ? 1 : 1 / 
range)

Review Comment:
   Could you please explain why this PR chooses to make scale  = 1 when range 
== 0? Spark seems to make scale = 0 in this case.



##########
flink-ml-lib/src/test/java/org/apache/flink/ml/feature/RobustScalerTest.java:
##########
@@ -0,0 +1,295 @@
+/*
+ * 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.robustscaler.RobustScaler;
+import org.apache.flink.ml.feature.robustscaler.RobustScalerModel;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.SparseVector;
+import org.apache.flink.ml.linalg.Vectors;
+import org.apache.flink.ml.util.TestUtils;
+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.Expressions;
+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.test.util.AbstractTestBase;
+import org.apache.flink.types.Row;
+
+import org.apache.commons.collections.IteratorUtils;
+import org.apache.commons.lang3.exception.ExceptionUtils;
+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.List;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+/** Tests {@link RobustScaler} and {@link RobustScalerModel}. */
+public class RobustScalerTest extends AbstractTestBase {
+    @Rule public final TemporaryFolder tempFolder = new TemporaryFolder();
+    private StreamExecutionEnvironment env;
+    private StreamTableEnvironment tEnv;
+    private Table trainDataTable;
+    private Table predictDataTable;
+
+    private static final List<Row> TRAIN_DATA =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Row.of(0, Vectors.dense(0.0, 0.0)),
+                            Row.of(1, Vectors.dense(1.0, -1.0)),
+                            Row.of(2, Vectors.dense(2.0, -2.0)),
+                            Row.of(3, Vectors.dense(3.0, -3.0)),
+                            Row.of(4, Vectors.dense(4.0, -4.0)),
+                            Row.of(5, Vectors.dense(5.0, -5.0)),
+                            Row.of(6, Vectors.dense(6.0, -6.0)),
+                            Row.of(7, Vectors.dense(7.0, -7.0)),
+                            Row.of(8, Vectors.dense(8.0, -8.0))));
+    private static final List<Row> PREDICT_DATA =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Row.of(Vectors.dense(3.0, -3.0)),
+                            Row.of(Vectors.dense(6.0, -6.0)),
+                            Row.of(Vectors.dense(99.0, -99.0))));
+    private static final double EPS = 1.0e-5;
+
+    private static final List<DenseVector> EXPECTED_OUTPUT =
+            new ArrayList<>(
+                    Arrays.asList(
+                            Vectors.dense(0.75, -0.75),
+                            Vectors.dense(1.5, -1.5),
+                            Vectors.dense(24.75, -24.75)));
+
+    @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);
+        trainDataTable = 
tEnv.fromDataStream(env.fromCollection(TRAIN_DATA)).as("id", "input");
+        predictDataTable = 
tEnv.fromDataStream(env.fromCollection(PREDICT_DATA)).as("input");
+    }
+
+    private static void verifyPredictionResult(
+            Table output, String outputCol, List<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());
+        compareResultCollections(expected, result, TestUtils::compare);
+    }
+
+    @Test
+    public void testParam() {
+        RobustScaler robustScaler = new RobustScaler();
+        assertEquals("input", robustScaler.getInputCol());
+        assertEquals("output", robustScaler.getOutputCol());
+        assertEquals(0.25, robustScaler.getLower(), EPS);
+        assertEquals(0.75, robustScaler.getUpper(), EPS);
+        assertEquals(0.001, robustScaler.getRelativeError(), EPS);
+        assertFalse(robustScaler.getWithCentering());
+        assertTrue(robustScaler.getWithScaling());
+
+        robustScaler
+                .setInputCol("test_input")
+                .setOutputCol("test_output")
+                .setLower(0.1)
+                .setUpper(0.9)
+                .setRelativeError(0.01)
+                .setWithCentering(false)

Review Comment:
   It might be better to set it to a non-default value.



##########
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/robustscaler/RobustScaler.java:
##########
@@ -0,0 +1,183 @@
+/*
+ * 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.robustscaler;
+
+import org.apache.flink.api.common.functions.AggregateFunction;
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.common.util.QuantileSummary;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vector;
+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.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.Preconditions;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Scale features using statistics that are robust to outliers.
+ *
+ * <p>This Scaler removes the median and scales the data according to the 
quantile range (defaults
+ * to IQR: Interquartile Range). The IQR is the range between the 1st quartile 
(25th quantile) and
+ * the 3rd quartile (75th quantile) but can be configured.
+ *
+ * <p>Centering and scaling happen independently on each feature by computing 
the relevant
+ * statistics on the samples in the training set. Median and quantile range 
are then stored to be
+ * used on later data using the transform method.
+ *
+ * <p>Standardization of a dataset is a common requirement for many machine 
learning estimators.
+ * Typically this is done by removing the mean and scaling to unit variance. 
However, outliers can
+ * often influence the sample mean / variance in a negative way. In such 
cases, the median and the
+ * interquartile range often give better results.

Review Comment:
   I guess "range" should be "ranges". Let's also check if there are other 
grammar errors.



##########
flink-ml-lib/src/main/java/org/apache/flink/ml/feature/robustscaler/RobustScaler.java:
##########
@@ -0,0 +1,183 @@
+/*
+ * 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.robustscaler;
+
+import org.apache.flink.api.common.functions.AggregateFunction;
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.ml.api.Estimator;
+import org.apache.flink.ml.common.datastream.DataStreamUtils;
+import org.apache.flink.ml.common.util.QuantileSummary;
+import org.apache.flink.ml.linalg.DenseVector;
+import org.apache.flink.ml.linalg.Vector;
+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.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.Preconditions;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Scale features using statistics that are robust to outliers.
+ *
+ * <p>This Scaler removes the median and scales the data according to the 
quantile range (defaults
+ * to IQR: Interquartile Range). The IQR is the range between the 1st quartile 
(25th quantile) and
+ * the 3rd quartile (75th quantile) but can be configured.
+ *
+ * <p>Centering and scaling happen independently on each feature by computing 
the relevant
+ * statistics on the samples in the training set. Median and quantile range 
are then stored to be
+ * used on later data using the transform method.
+ *
+ * <p>Standardization of a dataset is a common requirement for many machine 
learning estimators.
+ * Typically this is done by removing the mean and scaling to unit variance. 
However, outliers can
+ * often influence the sample mean / variance in a negative way. In such 
cases, the median and the
+ * interquartile range often give better results.
+ */
+public class RobustScaler
+        implements Estimator<RobustScaler, RobustScalerModel>, 
RobustScalerParams<RobustScaler> {
+    private final Map<Param<?>, Object> paramMap = new HashMap<>();
+
+    public RobustScaler() {
+        ParamUtils.initializeMapWithDefaultValues(paramMap, this);
+    }
+
+    @Override
+    public RobustScalerModel fit(Table... inputs) {
+        Preconditions.checkArgument(inputs.length == 1);
+        StreamTableEnvironment tEnv =
+                (StreamTableEnvironment) ((TableImpl) 
inputs[0]).getTableEnvironment();
+        DataStream<DenseVector> inputData =
+                tEnv.toDataStream(inputs[0])
+                        .map(
+                                (MapFunction<Row, DenseVector>)
+                                        value ->
+                                                ((Vector) 
value.getField(getInputCol())).toDense());

Review Comment:
   It might be better to create a final variable of `getInputCol()`'s value and 
read the value in this map function.



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