org.apache.hadoop.mapreduce.lib.fieldsel

类 FieldSelectionReducer<K,V>

java.lang.Object

org.apache.hadoop.mapreduce.Reducer<Text,Text,Text,Text>

org.apache.hadoop.mapreduce.lib.fieldsel.FieldSelectionReducer<K,V>

@InterfaceAudience.Public
@InterfaceStability.Stable
public class FieldSelectionReducer<K,V>
extends Reducer<Text,Text,Text,Text>

This class implements a reducer class that can be used to perform field selections in a manner similar to unix cut. The input data is treated as fields separated by a user specified separator (the default value is "\t"). The user can specify a list of fields that form the reduce output keys, and a list of fields that form the reduce output values. The fields are the union of those from the key and those from the value. The field separator is under attribute "mapreduce.fieldsel.data.field.separator" The reduce output field list spec is under attribute "mapreduce.fieldsel.reduce.output.key.value.fields.spec". The value is expected to be like "keyFieldsSpec:valueFieldsSpec" key/valueFieldsSpec are comma (,) separated field spec: fieldSpec,fieldSpec,fieldSpec ... Each field spec can be a simple number (e.g. 5) specifying a specific field, or a range (like 2-5) to specify a range of fields, or an open range (like 3-) specifying all the fields starting from field 3. The open range field spec applies value fields only. They have no effect on the key fields. Here is an example: "4,3,0,1:6,5,1-3,7-". It specifies to use fields 4,3,0 and 1 for keys, and use fields 6,5,1,2,3,7 and above for values.

嵌套类概要

从类继承的嵌套类/接口 org.apache.hadoop.mapreduce.Reducer

Reducer.Context

字段概要

字段

限定符和类型	字段和说明
static org.apache.commons.logging.Log	LOG

构造器概要

构造器

构造器和说明
FieldSelectionReducer()

方法概要

方法

限定符和类型	方法和说明
void	reduce(Text key, Iterable<Text> values, Reducer.Context context) This method is called once for each key.
void	setup(Reducer.Context context) Called once at the start of the task.

从类继承的方法 org.apache.hadoop.mapreduce.Reducer

cleanup, run

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

字段详细资料

LOG

public static final org.apache.commons.logging.Log LOG

构造器详细资料

FieldSelectionReducer

public FieldSelectionReducer()

方法详细资料

setup

public void setup(Reducer.Context context)
           throws IOException,
                  InterruptedException

从类复制的说明: Reducer

Called once at the start of the task.

覆盖:

setup 在类中 Reducer<Text,Text,Text,Text>

抛出:

IOException

InterruptedException

reduce

public void reduce(Text key,
          Iterable<Text> values,
          Reducer.Context context)
            throws IOException,
                   InterruptedException

从类复制的说明: Reducer

This method is called once for each key. Most applications will define their reduce class by overriding this method. The default implementation is an identity function.

覆盖:

reduce 在类中 Reducer<Text,Text,Text,Text>

抛出:

IOException

InterruptedException