ValueAggregatorBaseDescriptor (Hadoop 1.2.1 API)
Date: 2013-07-22

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## org.apache.hadoop.mapred.lib.aggregate
Class ValueAggregatorBaseDescriptor

    java.lang.Object
      org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorBaseDescriptor

All Implemented Interfaces:
  ValueAggregatorDescriptor

Direct Known Subclasses:
  AggregateWordCount.WordCountPlugInClass, AggregateWordHistogram.AggregateWordHistogramPlugin

    public class ValueAggregatorBaseDescriptor

extends Object
implements ValueAggregatorDescriptor

This class implements the common functionalities of the subclasses of ValueAggregatorDescriptor class.

Field Summary
`static String` | `DOUBLE_VALUE_SUM`
`String` | `inputFile`
`static String` | `LONG_VALUE_MAX`
`static String` | `LONG_VALUE_MIN`
`static String` | `LONG_VALUE_SUM`
`static String` | `STRING_VALUE_MAX`
`static String` | `STRING_VALUE_MIN`
`static String` | `UNIQ_VALUE_COUNT`
`static String` | `VALUE_HISTOGRAM`

Fields inherited from interface org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorDescriptor
`ONE, TYPE_SEPARATOR`

Constructor Summary
`ValueAggregatorBaseDescriptor()`

Method Summary
`void` | `configure(JobConf job)` get the input file name.
`static Map.Entry<Text,Text>` | `generateEntry(String type, String id, Text val)`
`ArrayList<Map.Entry<Text,Text>>` | `generateKeyValPairs(Object key, Object val)` Generate 1 or 2 aggregation-id/value pairs for the given key/value pair.
`static ValueAggregator` | `generateValueAggregator(String type)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### UNIQ_VALUE_COUNT

    public static final String UNIQ_VALUE_COUNT

See Also:
  Constant Field Values

### LONG_VALUE_SUM

    public static final String LONG_VALUE_SUM

See Also:
  Constant Field Values

### DOUBLE_VALUE_SUM

    public static final String DOUBLE_VALUE_SUM

See Also:
  Constant Field Values

### VALUE_HISTOGRAM

    public static final String VALUE_HISTOGRAM

See Also:
  Constant Field Values

### LONG_VALUE_MAX

    public static final String LONG_VALUE_MAX

See Also:
  Constant Field Values

### LONG_VALUE_MIN

    public static final String LONG_VALUE_MIN

See Also:
  Constant Field Values

### STRING_VALUE_MAX

    public static final String STRING_VALUE_MAX

See Also:
  Constant Field Values

### STRING_VALUE_MIN

    public static final String STRING_VALUE_MIN

See Also:
  Constant Field Values

### inputFile

    public String inputFile

Constructor Detail

### ValueAggregatorBaseDescriptor

    public ValueAggregatorBaseDescriptor()

Method Detail

### generateEntry

    public static Map.Entry<Text,Text> generateEntry(String type,
                                                     String id,
                                                     Text val)

  Parameters:
    `type` - the aggregation type
    `id` - the aggregation id
    `val` - the val associated with the id to be aggregated
  Returns:
    an Entry whose key is the aggregation id prefixed with the aggregation type.

### generateValueAggregator

    public static ValueAggregator generateValueAggregator(String type)

  Parameters:
    `type` - the aggregation type
  Returns:
    a value aggregator of the given type.

### generateKeyValPairs

    public ArrayList<Map.Entry<Text,Text>> generateKeyValPairs(Object key,
                                                               Object val)

  Generate 1 or 2 aggregation-id/value pairs for the given key/value pair. The first id will be of type LONG_VALUE_SUM, with "record_count" as its aggregation id. If the input is a file split, the second id of the same type will be generated too, with the file name as its aggregation id. This achieves the behavior of counting the total number of records in the input data, and the number of records in each input file.

  Specified by:
    `generateKeyValPairs` in interface `ValueAggregatorDescriptor`
  Parameters:
    `key` - input key
    `val` - 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

    public void configure(JobConf job)

  get the input file name.

  Specified by:
    `configure` in interface `ValueAggregatorDescriptor`
  Parameters:
    `job` - a job configuration object

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