Package net.sf.saxon.expr.sort

Class 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.

    • Constructor Detail

      • 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 Detail

      • 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<?>>

      • 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