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.

  • 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

    • currentGroup

      public GroundedValue currentGroup() throws XPathException
      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 interface GroupIterator
      Returns:
      a sequence containing all the members of the current group, in population order.
      Throws:
      XPathException - if a dynamic error occurs

    • getCurrentGroup

      public List<Item> getCurrentGroup()
      Get the contents of the current group as a java List
      Returns:
      the contents of the current group

    • 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 interface LookaheadIterator
      Returns:
      true if the LookaheadIterator.hasNext() method is available

    • 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 interface LookaheadIterator
      Returns:
      true if there are more items in the sequence

    • next

      public Item 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 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.

    • supportsGetLength

      public boolean supportsGetLength()
      Description copied from interface: LastPositionFinder
      Ask whether this iterator supports use of the LastPositionFinder.getLength() method. This method should always be called before calling LastPositionFinder.getLength(), because an iterator that implements this interface may support use of LastPositionFinder.getLength() in some situations and not in others
      Specified by:
      supportsGetLength in interface LastPositionFinder
      Returns:
      true if the LastPositionFinder.getLength() method can be called to determine the length of the underlying sequence.

    • getLength

      public int getLength()
      Get the last position (that is, the number of groups)
      Specified by:
      getLength in interface LastPositionFinder
      Returns:
      the number of items in the sequence

    • getSnapShot

      public ManualGroupIterator getSnapShot(XPathContext context)
      Description copied from interface: GroupIterator
      Get a pseudo-iterator which represents a snapshot of this sequence at the current position
      Specified by:
      getSnapShot in interface GroupIterator
      Parameters:
      context - the XPath context
      Returns:
      the snapshot sequence