org.apache.hadoop.mapred.lib.aggregate
Interface ValueAggregatorDescriptor
- All Known Implementing Classes:
- 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.
TYPE_SEPARATOR
static final String TYPE_SEPARATOR
- See Also:
- Constant Field Values
ONE
static final Text ONE
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.
- Parameters:
key
- input keyval
- input value
- Returns:
- 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
- Parameters:
job
- a JobConf object that may contain the information that can be used
to configure the object.
Copyright © 2009 The Apache Software Foundation