simpledb

Interface Aggregator

All Superinterfaces:

java.io.Serializable

All Known Implementing Classes:

IntegerAggregator, StringAggregator

public interface Aggregator
extends java.io.Serializable

The common interface for any class that can compute an aggregate over a list of Tuples.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	Aggregator.Op
static class	Aggregator.TupleMapIterator TupleMapIterator is class which converts HashMap < Field, Tuple > to a DbIterator.

Field Summary

Fields

Modifier and Type	Field and Description
static int	NO_GROUPING
static Field	noGroupField

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 for a distinct group value; creates a new group aggregate result if the group value has not yet been encountered.

Field Detail

NO_GROUPING

static final int NO_GROUPING

See Also:

Constant Field Values

noGroupField

static final Field noGroupField

Method Detail

mergeTupleIntoGroup

void mergeTupleIntoGroup(Tuple tup)

Merge a new tuple into the aggregate for a distinct group value; creates a new group aggregate result if the group value has not yet been encountered.

Parameters:

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

iterator

DbIterator iterator()

Create a DbIterator over group aggregate results.

See Also:

for a possible helper