net.sf.saxon.expr.sort

Class GroupByIterator

java.lang.Object

net.sf.saxon.expr.sort.GroupByIterator

All Implemented Interfaces:

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	GroupByIterator.ManualGroupByIterator

Field Summary

Fields

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

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

ATOMIZING, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

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

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close the iterator.
SequenceIterator	getAnother() Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
List	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)
int	getProperties() Get properties of this iterator, as a bit-significant integer.
ManualGroupIterator	getSnapShot(XPathContext context) Get a sequence which is a snapshot of this sequence at the current position
boolean	hasCurrentGroup() Ask whether this iterator has a current group
boolean	hasCurrentGroupingKey() Ask whether this iterator has a current grouping key
boolean	hasNext() Determine whether there are more items to come.
SequenceIterator	iterateCurrentGroup() Get an iterator over the items in the current group
Item	next() Get the next item in the sequence.

Methods inherited from class java.lang.Object

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

Field Detail

keyExpression

protected Expression keyExpression

groups

protected List<List<Item>> groups

groupKeys

protected List<AtomicSequence> groupKeys

groupSlot

protected int groupSlot

keySlot

protected int keySlot

composite

protected boolean composite

Constructor Detail

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 Detail

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

iterateCurrentGroup

public SequenceIterator iterateCurrentGroup()

Get an iterator over the items in the current group

Specified by:

iterateCurrentGroup in interface GroupIterator

Returns:

the iterator

hasCurrentGroup

public boolean hasCurrentGroup()

Description copied from interface: GroupIterator

Ask whether this iterator has a current group

Specified by:

hasCurrentGroup in interface GroupIterator

Returns:

false if the controlling xsl:for-each-group element binds a group variable, true if it delivers results using the current-group() function

hasCurrentGroupingKey

public boolean hasCurrentGroupingKey()

Description copied from interface: GroupIterator

Ask whether this iterator has a current grouping key

Specified by:

hasCurrentGroupingKey in interface GroupIterator

Returns:

false if the controlling xsl:for-each-group element binds a grouping-key variable, true if it delivers results using the current-grouping-key() function

getCurrentGroup

public List getCurrentGroup()

Get the contents of the current group as a java List

Returns:

the contents of the current group

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 getProperties() on the iterator includes the bit setting SequenceIterator.LOOKAHEAD

Specified by:

hasNext in interface LookaheadIterator

Returns:

true if there are more items in the sequence

next

public Item next()
          throws XPathException

Description copied from interface: SequenceIterator

Get the next item in the sequence. This method changes the state of the iterator, in particular it affects the result of subsequent calls of position() and current().

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.

Throws:

XPathException - if an error occurs retrieving the next item

close

public void close()

Description copied from interface: SequenceIterator

Close the iterator. This indicates to the supplier of the data that the client does not require any more items to be delivered by the iterator. This may enable the supplier to release resources. After calling close(), no further calls on the iterator should be made; if further calls are made, the effect of such calls is undefined.

(Currently, closing an iterator is important only when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.)

Specified by:

close in interface SequenceIterator

getAnother

public SequenceIterator getAnother()
                            throws XPathException

Description copied from interface: SequenceIterator

Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.

This method allows access to all the items in the sequence without disturbing the current position of the iterator. Internally, its main use is in evaluating the last() function.

This method does not change the state of the iterator.

Some implementations of this method may regenerate the input sequence, creating new nodes with different identity from the original. This is not recommended, but is hard to prevent. This causes no problem for the primary usage of this method to support the last() function, but it has been known to cause trouble in other situations.

Specified by:

getAnother in interface SequenceIterator

Returns:

a SequenceIterator that iterates over the same items, positioned before the first item

Throws:

XPathException - if any error occurs

getProperties

public int getProperties()

Get properties of this iterator, as a bit-significant integer.

Specified by:

getProperties in interface SequenceIterator

Returns:

the properties of this iterator. This will be some combination of properties such as SequenceIterator.GROUNDED, SequenceIterator.LAST_POSITION_FINDER, and SequenceIterator.LOOKAHEAD. It is always acceptable to return the value zero, indicating that there are no known special properties. It is acceptable for the properties of the iterator to change depending on its state.

getLength

public int getLength()
              throws XPathException

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

Specified by:

getLength in interface LastPositionFinder

Returns:

the number of items in the sequence

Throws:

XPathException - if an error occurs evaluating the sequence in order to determine the number of items

getSnapShot

public ManualGroupIterator getSnapShot(XPathContext context)
                                throws XPathException

Description copied from interface: GroupIterator

Get a sequence which is a snapshot of this sequence at the current position

Specified by:

getSnapShot in interface GroupIterator

Throws:

XPathException