[GitHub] flink pull request: [FLINK-1398] Introduce extractSingleField() in...

[fhueske <gi...@git.apache.org>]

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/308#discussion_r28776433
  
    --- Diff: flink-java/src/main/java/org/apache/flink/api/java/lib/DataSetUtil.java ---
    @@ -0,0 +1,85 @@
    +/*
    + * 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.api.java.lib;
    +
    +
    +import org.apache.flink.api.common.functions.MapFunction;
    +import org.apache.flink.api.java.DataSet;
    +import org.apache.flink.api.java.operators.MapOperator;
    +import org.apache.flink.api.java.operators.SingleInputUdfOperator;
    +import org.apache.flink.api.java.tuple.Tuple;
    +import org.apache.flink.api.java.typeutils.TupleTypeInfo;
    +import org.apache.flink.api.java.typeutils.TypeExtractor;
    +
    +
    +public class DataSetUtil {
    +
    +	
    +	// --------------------------------------------------------------------------------------------
    +	//  Extraction of a single field
    +	// --------------------------------------------------------------------------------------------
    +
    +	/**
    +	 * Applies a single field extraction on a {@link Tuple} {@link DataSet}.<br/>
    +	 * <b>Note: Can be only applied on Tuple DataSets using the corresponding field index.</b></br>
    +	 * The transformation extracts of each Tuple of the DataSet a given field.</br>
    +	 *
    +	 *
    +	 * @param ds The input DataSet.
    +	 * @param fieldIndex The field index of the input tuple which is extracted.
    +	 * @param outputType Class of the extracted field.   
    +	 * @return A SingleInputUdfOperator that represents the extracted field.
    +	 *
    +	 * @see Tuple
    +	 * @see DataSet
    +	 * @see org.apache.flink.api.java.operators.SingleInputUdfOperator
    +	 */
    +	public static <IN extends Tuple, OUT> SingleInputUdfOperator<IN, OUT, MapOperator<IN, OUT>> extractSingleField(DataSet<IN> ds, int fieldIndex, Class<OUT> outputType) {
    +
    +		if(!ds.getType().isTupleType()) {
    +			throw new IllegalArgumentException("The DataSet has to contain a Tuple, not " + ds.getType().getTypeClass().getName());
    +		}
    +		
    +		TupleTypeInfo<IN> tupleInfo = (TupleTypeInfo) ds.getType();
    +		if(fieldIndex >= tupleInfo.getArity() || fieldIndex < 0) {
    +			throw new IndexOutOfBoundsException("The field index has to be between 0 and " + (tupleInfo.getArity()-1));
    +		}
    +		
    +		if(!tupleInfo.getTypeAt(fieldIndex).equals(TypeExtractor.createTypeInfo(outputType))) {
    +			throw new IllegalArgumentException("The output class type has to be: " + tupleInfo.getTypeAt(fieldIndex).toString());
    +		}
    +		
    +		return ds.map(new ExtractElement(fieldIndex)).returns(tupleInfo.getTypeAt(fieldIndex));
    --- End diff --
    
    Add `.name("Extract Field "+fieldIndex)` to specify the name of the Map operator.


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