simpledb

Class StringAggregator

java.lang.Object

simpledb.StringAggregator

All Implemented Interfaces:

java.io.Serializable, Aggregator

public class StringAggregator
extends java.lang.Object
implements Aggregator

Knows how to compute some aggregate over a set of StringFields.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface simpledb.Aggregator

Aggregator.Op, Aggregator.TupleMapIterator

Field Summary

Fields

Modifier and Type	Field and Description
private int	aField
private java.util.HashMap<Field,Tuple>	fieldTupleMap
private int	gbField
private Type	gbFieldType
private Aggregator.Op	op
private static long	serialVersionUID
private TupleDesc	tupleDesc

Fields inherited from interface simpledb.Aggregator

NO_GROUPING, noGroupField

Constructor Summary

Constructors

Constructor and Description
StringAggregator(int gbfield, Type gbfieldtype, int afield, Aggregator.Op what) Aggregate constructor

Method Summary

Modifier and Type	Method and Description
DbIterator	iterator() Create a DbIterator over group aggregate results.
void	mergeTupleIntoGroup(Tuple tup) Merge a new tuple into the aggregate, grouping as indicated in the constructor

Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

gbField

private int gbField

aField

private int aField

op

private Aggregator.Op op

gbFieldType

private Type gbFieldType

tupleDesc

private TupleDesc tupleDesc

fieldTupleMap

private java.util.HashMap<Field,Tuple> fieldTupleMap

Constructor Detail

StringAggregator

public StringAggregator(int gbfield,
                        Type gbfieldtype,
                        int afield,
                        Aggregator.Op what)

Aggregate constructor

Parameters:

gbfield - the 0-based index of the group-by field in the tuple, or NO_GROUPING if there is no grouping

gbfieldtype - the type of the group by field (e.g., Type.INT_TYPE), or null if there is no grouping

afield - the 0-based index of the aggregate field in the tuple

what - aggregation operator to use -- only supports COUNT

Throws:

java.lang.IllegalArgumentException - if what != COUNT

Method Detail

mergeTupleIntoGroup

public void mergeTupleIntoGroup(Tuple tup)

Merge a new tuple into the aggregate, grouping as indicated in the constructor

Specified by:

mergeTupleIntoGroup in interface Aggregator

Parameters:

tup - the Tuple containing an aggregate field and a group-by field

iterator

public DbIterator iterator()

Create a DbIterator over group aggregate results.

Specified by:

iterator in interface Aggregator

Returns:

a DbIterator whose tuples are the pair (groupVal, aggregateVal) if using group, or a single (aggregateVal) if no grouping. The aggregateVal is determined by the type of aggregate specified in the constructor.

See Also:

for a possible helper