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<Item<?>>, LookaheadIterator<Item<?>>
public class GroupByIterator extends Object implements GroupIterator, LastPositionFinder, LookaheadIterator<Item<?>>
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 Details

  • 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

    • iterateCurrentGroup

      public SequenceIterator<?> iterateCurrentGroup()
      Get an iterator over the items in the current group
      Specified by:
      iterateCurrentGroup in interface GroupIterator
      Returns:
      the iterator

    • 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<Item<?>>
      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.
      Specified by:
      next in interface SequenceIterator<Item<?>>
      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.

      For example, the iterator returned by the unparsed-text-lines() function has a close() method that causes the underlying input stream to be closed, whether or not the file has been read to completion.

      Closing an iterator is important 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 AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in interface SequenceIterator<Item<?>>

    • getProperties

      public int getProperties()
      Get properties of this iterator, as a bit-significant integer.
      Specified by:
      getProperties in interface SequenceIterator<Item<?>>
      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