[GitHub] [flink] walterddr commented on a change in pull request #9355: [FLINK-13577][ml] Add an util class to build result row and generate …

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walterddr commented on a change in pull request #9355: [FLINK-13577][ml] Add an util class to build result row and generate …
URL: https://github.com/apache/flink/pull/9355#discussion_r342379204
 
 

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 File path: flink-ml-parent/flink-ml-lib/src/main/java/org/apache/flink/ml/common/utils/OutputColsHelper.java
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+/*
+ * 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.common.utils;
+
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.table.api.TableSchema;
+import org.apache.flink.types.Row;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+
+/**
+ * Util for generating output schema when doing prediction or transformation.
+ *
+ * <p>Input:
+ * 1) Schema of input data being predicted or transformed.
+ * 2) Output column names of the prediction/transformation operator.
+ * 3) Output column types of the prediction/transformation operator.
+ * 4) Reserved column names, which is a subset of input data's column names that we want to preserve.
+ *
+ * <p>Output:
+ * 1）The result data schema. The result data is a combination of the preserved columns and the operator's
+ * output columns.
+ *
+ * <p>Several rules are followed:
+ * 1) If reserved columns are not given, then all columns of input data is reserved.
 
 Review comment:
   I think this is actually the one default that confuses me: why if reserved columns are not given then preserves all input data? 

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