org.apache.hadoop.mapreduce.lib.fieldsel

クラス 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.

フィールドのサマリー

フィールド

修飾子とタイプ	フィールドと説明
static org.apache.commons.logging.Log	LOG

コンストラクタのサマリー

コンストラクタ

コンストラクタと説明
FieldSelectionReducer()

メソッドのサマリー

修飾子とタイプ	メソッドと説明
void	reduce(Text key, Iterable<Text> values, org.apache.hadoop.mapreduce.Reducer.Context context) This method is called once for each key.
void	setup(org.apache.hadoop.mapreduce.Reducer.Context context) Called once at the start of the task.

クラスから継承されたメソッド org.apache.hadoop.mapreduce.Reducer

cleanup, run

クラスから継承されたメソッド java.lang.Object

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

フィールドの詳細

LOG

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

コンストラクタの詳細

FieldSelectionReducer

public FieldSelectionReducer()

メソッドの詳細

setup

public void setup(org.apache.hadoop.mapreduce.Reducer.Context context)
           throws IOException,
                  InterruptedException

クラスからコピーされた説明: Reducer

Called once at the start of the task.

オーバーライド:

setup クラス内 Reducer<Text,Text,Text,Text>

例外:

IOException

InterruptedException

reduce

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

クラスからコピーされた説明: 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.

オーバーライド:

reduce クラス内 Reducer<Text,Text,Text,Text>

例外:

IOException

InterruptedException