public class FieldSelectionMapReduce<K,V> extends Object implements Mapper<K,V,Text,Text>, Reducer<Text,Text,Text,Text>
限定符和类型 | 字段和说明 |
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static org.apache.commons.logging.Log |
LOG |
构造器和说明 |
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FieldSelectionMapReduce() |
限定符和类型 | 方法和说明 |
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void |
close() |
void |
configure(JobConf job)
Initializes a new instance from a
JobConf . |
void |
map(K key,
V val,
OutputCollector<Text,Text> output,
Reporter reporter)
The identify function.
|
void |
reduce(Text key,
Iterator<Text> values,
OutputCollector<Text,Text> output,
Reporter reporter)
Reduces values for a given key.
|
public void map(K key, V val, OutputCollector<Text,Text> output, Reporter reporter) throws IOException
public void configure(JobConf job)
JobConfigurable
JobConf
.configure
在接口中 JobConfigurable
job
- the configurationpublic void close() throws IOException
close
在接口中 Closeable
close
在接口中 AutoCloseable
IOException
public void reduce(Text key, Iterator<Text> values, OutputCollector<Text,Text> output, Reporter reporter) throws IOException
Reducer
The framework calls this method for each
<key, (list of values)>
pair in the grouped inputs.
Output values must be of the same type as input values. Input keys must
not be altered. The framework will reuse the key and value objects
that are passed into the reduce, therefore the application should clone
the objects they want to keep a copy of. In many cases, all values are
combined into zero or one value.
Output pairs are collected with calls to
OutputCollector.collect(Object,Object)
.
Applications can use the Reporter
provided to report progress
or just indicate that they are alive. In scenarios where the application
takes an insignificant amount of time to process individual key/value
pairs, this is crucial since the framework might assume that the task has
timed-out and kill that task. The other way of avoiding this is to set
mapred.task.timeout to a high-enough value (or even zero for no
time-outs).
Copyright © 2009 The Apache Software Foundation