org.apache.hadoop.mapred.lib.aggregate

接口 ValueAggregatorDescriptor

所有已知实现类:

AggregateWordCount.WordCountPlugInClass, AggregateWordHistogram.AggregateWordHistogramPlugin, UserDefinedValueAggregatorDescriptor, ValueAggregatorBaseDescriptor

public interface ValueAggregatorDescriptor

This interface defines the contract a value aggregator descriptor must support. Such a descriptor can be configured with a JobConf object. Its main function is to generate a list of aggregation-id/value pairs. An aggregation id encodes an aggregation type which is used to guide the way to aggregate the value in the reduce/combiner phrase of an Aggregate based job.The mapper in an Aggregate based map/reduce job may create one or more of ValueAggregatorDescriptor objects at configuration time. For each input key/value pair, the mapper will use those objects to create aggregation id/value pairs.

字段概要

字段

限定符和类型	字段和说明
static Text	ONE
static String	TYPE_SEPARATOR

方法概要

方法

限定符和类型	方法和说明
void	configure(JobConf job) Configure the object
ArrayList<Map.Entry<Text,Text>>	generateKeyValPairs(Object key, Object val) Generate a list of aggregation-id/value pairs for the given key/value pair.

字段详细资料

TYPE_SEPARATOR

static final String TYPE_SEPARATOR

另请参阅:

常量字段值

ONE

static final Text ONE

方法详细资料

generateKeyValPairs

ArrayList<Map.Entry<Text,Text>> generateKeyValPairs(Object key,
                                                  Object val)

Generate a list of aggregation-id/value pairs for the given key/value pair. This function is usually called by the mapper of an Aggregate based job.

参数:

key - input key

val - input value

返回:

a list of aggregation id/value pairs. An aggregation id encodes an aggregation type which is used to guide the way to aggregate the value in the reduce/combiner phrase of an Aggregate based job.

configure

void configure(JobConf job)

Configure the object

参数:

job - a JobConf object that may contain the information that can be used to configure the object.