[转载]Hadoop Streaming 实战： aggregate
http://blog.csdn.net/yfkiss/article/details/70190222. aggregate class summary
DoubleValueSumThis class implements a value aggregator that sums up a sequence of double values.LongValueMaxThis class implements a value aggregator that maintain the maximum of a sequence of long values.LongValueMinThis class implements a value aggregator that maintain the minimum of a sequence of long values.LongValueSumThis class implements a value aggregator that sums up a sequence of long values.StringValueMaxThis class implements a value aggregator that maintain the biggest of a sequence of strings.StringValueMinThis class implements a value aggregator that maintain the smallest of a sequence of strings.UniqValueCountThis class implements a value aggregator that dedupes a sequence of objects.UserDefinedValueAggregatorDescriptorThis class implements a wrapper for a user defined value aggregator descriptor.ValueAggregatorBaseDescriptorThis class implements the common functionalities of the subclasses of ValueAggregatorDescriptor class.ValueAggregatorCombiner<K1 extends WritableComparable,V1 extends Writable>This class implements the generic combiner of Aggregate.ValueAggregatorJobThis is the main class for creating a map/reduce job using Aggregate framework.ValueAggregatorJobBase<K1 extends WritableComparable,V1 extends Writable>This abstract class implements some common functionalities of the the generic mapper, reducer and combiner classes of Aggregate.ValueAggregatorMapper<K1 extends WritableComparable,V1 extends Writable>This class implements the generic mapper of Aggregate.ValueAggregatorReducer<K1 extends WritableComparable,V1 extends Writable>This class implements the generic reducer of Aggregate.ValueHistogramThis class implements a value aggregator that computes the histogram of a sequence of strings 3. streaming中使用aggregate
在mapper任务的输出中添加控制，如下：
function：key\tvalue
eg：
LongValueSum：key\tvalue
此外，置-reducer = aggregate。此时，Reducer使用aggregate中对应的function类对相同key的value进行操作，例如，设置function为LongValueSum则将对每个键值对应的value求和。
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