org.apache.hadoop.mapreduce.lib.fieldsel

クラス FieldSelectionMapper<K,V>

java.lang.Object

org.apache.hadoop.mapreduce.Mapper<K,V,Text,Text>

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

@InterfaceAudience.Public
 @InterfaceStability.Stable
public class FieldSelectionMapper<K,V>
extends Mapper<K,V,Text,Text>

This class implements a mapper 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 map output keys, and a list of fields that form the map output values. If the inputformat is TextInputFormat, the mapper will ignore the key to the map function. and the fields are from the value only. Otherwise, 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 map output field list spec is under attribute "mapreduce.fieldsel.map.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
FieldSelectionMapper()

メソッドのサマリー

修飾子とタイプ	メソッドと説明
void	map(K key, V val, org.apache.hadoop.mapreduce.Mapper.Context context) The identify function.
void	setup(org.apache.hadoop.mapreduce.Mapper.Context context) Called once at the beginning of the task.

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

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

FieldSelectionMapper

public FieldSelectionMapper()

メソッドの詳細

setup

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

クラスからコピーされた説明: Mapper

Called once at the beginning of the task.

オーバーライド:

setup クラス内 Mapper<K,V,Text,Text>

例外:

IOException

InterruptedException

map

public void map(K key,
                V val,
                org.apache.hadoop.mapreduce.Mapper.Context context)
         throws IOException,
                InterruptedException

The identify function. Input key/value pair is written directly to output.

オーバーライド:

map クラス内 Mapper<K,V,Text,Text>

例外:

IOException

InterruptedException