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	id ADDE4E1854; Tue, 10 Mar 2015 13:27:51 +0000 (UTC)
From: mxm <git@git.apache.org>
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References: <git-pr-466-flink@git.apache.org>
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Subject: [GitHub] flink pull request: [FLINK-1622][java-api][scala-api] add a
 partia...
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Message-Id: <20150310132751.ADDE4E1854@git1-us-west.apache.org>
Date: Tue, 10 Mar 2015 13:27:51 +0000 (UTC)
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Github user mxm commented on a diff in the pull request:

    https://github.com/apache/flink/pull/466#discussion_r26120661
  
    --- Diff: flink-java/src/main/java/org/apache/flink/api/java/operators/SortedGrouping.java ---
    @@ -156,6 +156,23 @@ public SortedGrouping(DataSet<T> set, Keys<T> keys, String field, Order order) {
     		return new GroupReduceOperator<T, R>(this, resultType, dataSet.clean(reducer), Utils.getCallLocationName() );
     	}
     
    +	/**
    +	 * Applies a partial GroupReduce transformation on a grouped and sorted {@link DataSet}.
    +	 *
    +	 * In contrast to the reduceGroup transformation, the GroupReduce function is only called on each partition. Thus,
    +	 * partial solutions are likely to occur.
    +	 * @param reducer The ReduceFunction that is applied on the DataSet.
    +	 * @return A GroupReducePartial operator which represents the partially reduced DataSet.
    +	 */
    +	public <R> GroupReducePartialOperator<T, R> reduceGroupPartially(GroupReduceFunction<T, R> reducer) {
    +		if (reducer == null) {
    +			throw new NullPointerException("GroupReduce function must not be null.");
    +		}
    +		TypeInformation<R> resultType = TypeExtractor.getGroupReduceReturnTypes(reducer, this.getDataSet().getType());
    +
    +		return new GroupReducePartialOperator<T, R>(this, resultType, dataSet.clean(reducer), Utils.getCallLocationName());
    +	}
    +
    --- End diff --
    
    We need a grouping to combine the correct values, don't we? Otherwise, we would perform an AllReduce.


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