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.
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected boolean
protected List
<AtomicSequence> protected Expression
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Constructor Summary
ConstructorsConstructorDescriptionGroupByIterator
(SequenceIterator population, Expression keyExpression, XPathContext keyContext, StringCollator collator, boolean composite) Create a GroupByIterator -
Method Summary
Modifier and TypeMethodDescriptionGet a sequence containing the members of the current group, in population order.Get the contents of the current group as a java ListGet the value of the grouping key for the current groupint
Get the last position (that is, the number of groups)getSnapShot
(XPathContext context) Get a pseudo-iterator which represents a snapshot of this sequence at the current positionboolean
hasNext()
Determine whether there are more items to come.next()
Get the next item in the sequence.boolean
Ask whether this iterator supports use of theLastPositionFinder.getLength()
method.boolean
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
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Field Details
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keyExpression
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groups
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groupKeys
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composite
protected boolean composite
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Constructor Details
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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 groupedkeyExpression
- the expression used to calculate the grouping keykeyContext
- dynamic context for calculating the grouping keycollator
- Collation to be used for comparing grouping keyscomposite
- true if grouping keys are to be treated as composite keys- Throws:
XPathException
- if an error occurs
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GroupByIterator
public GroupByIterator()
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Method Details
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getCurrentGroupingKey
Get the value of the grouping key for the current group- Specified by:
getCurrentGroupingKey
in interfaceGroupIterator
- Returns:
- the grouping key
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currentGroup
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 interfaceGroupIterator
- Returns:
- a sequence containing all the members of the current group, in population order.
- Throws:
XPathException
- if a dynamic error occurs
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getCurrentGroup
Get the contents of the current group as a java List- Returns:
- the contents of the current group
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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 interfaceLookaheadIterator
- Returns:
- true if the
LookaheadIterator.hasNext()
method is available
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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 interfaceLookaheadIterator
- Returns:
- true if there are more items in the sequence
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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 interfaceSequenceIterator
- 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.
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supportsGetLength
public boolean supportsGetLength()Description copied from interface:LastPositionFinder
Ask whether this iterator supports use of theLastPositionFinder.getLength()
method. This method should always be called before callingLastPositionFinder.getLength()
, because an iterator that implements this interface may support use ofLastPositionFinder.getLength()
in some situations and not in others- Specified by:
supportsGetLength
in interfaceLastPositionFinder
- Returns:
- true if the
LastPositionFinder.getLength()
method can be called to determine the length of the underlying sequence.
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getLength
public int getLength()Get the last position (that is, the number of groups)- Specified by:
getLength
in interfaceLastPositionFinder
- Returns:
- the number of items in the sequence
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getSnapShot
Description copied from interface:GroupIterator
Get a pseudo-iterator which represents a snapshot of this sequence at the current position- Specified by:
getSnapShot
in interfaceGroupIterator
- Parameters:
context
- the XPath context- Returns:
- the snapshot sequence
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