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java.lang.Object net.sf.saxon.expr.sort.GroupByIterator
public class GroupByIterator
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 | |
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protected AtomicComparer |
comparer
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protected List<AtomicValue> |
groupKeys
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protected List<List<Item>> |
groups
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protected Expression |
keyExpression
|
Fields inherited from interface net.sf.saxon.om.SequenceIterator |
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GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD |
Constructor Summary | |
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GroupByIterator(SequenceIterator population,
Expression keyExpression,
XPathContext keyContext,
StringCollator collator)
Create a GroupByIterator |
Method Summary | |
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void |
close()
Close the iterator. |
Item |
current()
Get the current value in the sequence (the one returned by the most recent call on next()). |
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 |
Value |
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. |
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. |
int |
position()
Get the current position. |
protected void |
processItem(HashMap<ComparisonKey,List<Item>> index,
Item item,
XPathContext c2)
Process one item in the population |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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protected Expression keyExpression
protected List<List<Item>> groups
protected List<AtomicValue> groupKeys
protected AtomicComparer comparer
Constructor Detail |
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public GroupByIterator(SequenceIterator population, Expression keyExpression, XPathContext keyContext, StringCollator collator) 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 keys
XPathException
Method Detail |
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protected void processItem(HashMap<ComparisonKey,List<Item>> index, Item item, XPathContext c2) throws XPathException
index
- the index of itemsitem
- the item from the population to be processedc2
- the XPath evaluation context
XPathException
public Value getCurrentGroupingKey()
getCurrentGroupingKey
in interface GroupIterator
public SequenceIterator iterateCurrentGroup()
iterateCurrentGroup
in interface GroupIterator
public 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 Item current()
SequenceIterator
current
in interface SequenceIterator
public int position()
SequenceIterator
This method does not change the state of the iterator.
position
in interface SequenceIterator
public 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 SequenceIterator getAnother() throws XPathException
SequenceIterator
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.
getAnother
in interface SequenceIterator
XPathException
- if any error occurspublic 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 items
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