Package net.sf.saxon.expr.sort

Class GroupByIterator

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, LastPositionFinder, GroupIterator, SequenceIterator, LookaheadIterator
    public class GroupByIterator
extends java.lang.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 Detail

      • keyExpression

        protected Expression keyExpression

      • groups

        protected java.util.List<java.util.List<Item>> groups

      • composite

        protected boolean composite

    • 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

      • 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 java.util.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.

      • 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