Package net.sf.saxon.expr.sort

Class GroupByIterator

java.lang.Object

net.sf.saxon.expr.sort.GroupByIterator

All Implemented Interfaces:

Closeable, AutoCloseable, LastPositionFinder, GroupIterator, SequenceIterator, LookaheadIterator

public class GroupByIterator
extends Object
implements GroupIterator, LastPositionFinder, LookaheadIterator

A GroupByIterator iterates over a sequence of groups defined by xsl:for-each-group group-by="x". The groups are returned in order of first appearance. Note that an item can appear in several groups; indeed, an item may be the leading item of more than one group, which means that knowing the leading item is not enough to know the current group.

The GroupByIterator acts as a SequenceIterator, where successive calls of next() return the leading item of each group in turn. The current item of the iterator is therefore the leading item of the current group. To get access to all the members of the current group, the method iterateCurrentGroup() is used; this underpins the current-group() function in XSLT. The grouping key for the current group is available via the getCurrentGroupingKey() method.

Field Summary

Fields

Modifier and Type	Field	Description
protected boolean	composite
protected List<AtomicSequence>	groupKeys
protected List<List<Item>>	groups
protected Expression	keyExpression

Constructor Summary

Constructors

Constructor	Description
GroupByIterator()
GroupByIterator(SequenceIterator population, Expression keyExpression, XPathContext keyContext, StringCollator collator, boolean composite)	Create a GroupByIterator

Method Summary

Modifier and Type	Method	Description
GroundedValue	currentGroup()	Get a sequence containing the members of the current group, in population order.
List<Item>	getCurrentGroup()	Get the contents of the current group as a java List
AtomicSequence	getCurrentGroupingKey()	Get the value of the grouping key for the current group
int	getLength()	Get the last position (that is, the number of groups)
ManualGroupIterator	getSnapShot(XPathContext context)	Get a pseudo-iterator which represents a snapshot of this sequence at the current position
boolean	hasNext()	Determine whether there are more items to come.
Item	next()	Get the next item in the sequence.
boolean	supportsGetLength()	Ask whether this iterator supports use of the LastPositionFinder.getLength() method.
boolean	supportsHasNext()	Ask whether the hasNext() method can be called.

Methods inherited from class java.lang.Object

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

Methods inherited from interface net.sf.saxon.om.SequenceIterator

close

Field Details

keyExpression

protected Expression keyExpression

groups

protected List<List<Item>> groups

groupKeys

protected List<AtomicSequence> groupKeys

composite

protected boolean composite

Constructor Details

GroupByIterator

public GroupByIterator(SequenceIterator population,
 Expression keyExpression,
 XPathContext keyContext,
 StringCollator collator,
 boolean composite)
                throws XPathException

Create a GroupByIterator

Parameters:

population - iterator over the population to be grouped

keyExpression - the expression used to calculate the grouping key

keyContext - dynamic context for calculating the grouping key

collator - Collation to be used for comparing grouping keys

composite - true if grouping keys are to be treated as composite keys

Throws:

XPathException - if an error occurs

GroupByIterator

public GroupByIterator()

Method Details

getCurrentGroupingKey

public AtomicSequence getCurrentGroupingKey()

Get the value of the grouping key for the current group

Specified by:

getCurrentGroupingKey in interface GroupIterator

Returns:

the grouping key

currentGroup

public GroundedValue currentGroup()
                           throws XPathException

Description copied from interface: GroupIterator

Get a sequence containing the members of the current group, in population order. This may be a MemoSequence rather than a grounded value

Specified by:

currentGroup in interface GroupIterator

Returns:

a sequence containing all the members of the current group, in population order.

Throws:

XPathException - if a dynamic error occurs

getCurrentGroup

public List<Item> getCurrentGroup()

Get the contents of the current group as a java List

Returns:

the contents of the current group

supportsHasNext

public boolean supportsHasNext()

Description copied from interface: LookaheadIterator

Ask whether the hasNext() method can be called. This method must be called before calling hasNext(), because some iterators implement this interface, but only support look-ahead under particular circumstances (this is usually because they delegate to another iterator)

Specified by:

supportsHasNext in interface LookaheadIterator

Returns:

true if the LookaheadIterator.hasNext() method is available

hasNext

public boolean hasNext()

Description copied from interface: LookaheadIterator

Determine whether there are more items to come. Note that this operation is stateless and it is not necessary (or usual) to call it before calling next(). It is used only when there is an explicit need to tell if we are at the last element.

This method must not be called unless the result of LookaheadIterator.supportsHasNext() is true.

Specified by:

hasNext in interface LookaheadIterator

Returns:

true if there are more items in the sequence

next

public Item next()

Description copied from interface: SequenceIterator

Get the next item in the sequence. This method changes the state of the iterator.

Specified by:

next in interface SequenceIterator

Returns:

the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.

supportsGetLength

public boolean supportsGetLength()

Description copied from interface: LastPositionFinder

Ask whether this iterator supports use of the LastPositionFinder.getLength() method. This method should always be called before calling LastPositionFinder.getLength(), because an iterator that implements this interface may support use of LastPositionFinder.getLength() in some situations and not in others

Specified by:

supportsGetLength in interface LastPositionFinder

Returns:

true if the LastPositionFinder.getLength() method can be called to determine the length of the underlying sequence.

getLength

public int getLength()

Get the last position (that is, the number of groups)

Specified by:

getLength in interface LastPositionFinder

Returns:

the number of items in the sequence

getSnapShot

public ManualGroupIterator getSnapShot(XPathContext context)

Description copied from interface: GroupIterator

Get a pseudo-iterator which represents a snapshot of this sequence at the current position

Specified by:

getSnapShot in interface GroupIterator

Parameters:

context - the XPath context

Returns:

the snapshot sequence