public class GroupByIterator extends java.lang.Object implements GroupIterator, LastPositionFinder, LookaheadIterator
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.
Modifier and Type | Class and Description |
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class |
GroupByIterator.ManualGroupByIterator |
Modifier and Type | Field and Description |
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protected boolean |
composite |
protected java.util.List<AtomicSequence> |
groupKeys |
protected java.util.List<java.util.List<Item>> |
groups |
protected Expression |
keyExpression |
ATOMIZING, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD
Constructor and Description |
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GroupByIterator() |
GroupByIterator(SequenceIterator population,
Expression keyExpression,
XPathContext keyContext,
StringCollator collator,
boolean composite)
Create a GroupByIterator
|
Modifier and Type | Method and Description |
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void |
close()
Close the iterator.
|
java.util.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 |
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.
|
protected Expression keyExpression
protected java.util.List<java.util.List<Item>> groups
protected java.util.List<AtomicSequence> groupKeys
protected boolean composite
public GroupByIterator(SequenceIterator population, Expression keyExpression, XPathContext keyContext, StringCollator collator, boolean composite) throws XPathException
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 keysXPathException
- if an error occurspublic GroupByIterator()
public AtomicSequence getCurrentGroupingKey()
getCurrentGroupingKey
in interface GroupIterator
public SequenceIterator iterateCurrentGroup()
iterateCurrentGroup
in interface GroupIterator
public java.util.List getCurrentGroup()
public boolean hasNext()
LookaheadIterator
SequenceIterator.LOOKAHEAD
hasNext
in interface LookaheadIterator
public Item next() throws XPathException
SequenceIterator
next
in interface SequenceIterator
XPathException
- if an error occurs retrieving the next itempublic void close()
SequenceIterator
(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.)
close
in interface SequenceIterator
public int getProperties()
getProperties
in interface SequenceIterator
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.public int getLength() throws XPathException
getLength
in interface LastPositionFinder
XPathException
- if an error occurs evaluating the sequence in order to determine
the number of itemspublic ManualGroupIterator getSnapShot(XPathContext context) throws XPathException
GroupIterator
getSnapShot
in interface GroupIterator
XPathException
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