Package it.unimi.dsi.webgraph.labelling

Class UnionArcLabelledImmutableGraph

java.lang.Object
it.unimi.dsi.webgraph.ImmutableGraph
it.unimi.dsi.webgraph.labelling.ArcLabelledImmutableGraph
it.unimi.dsi.webgraph.labelling.UnionArcLabelledImmutableGraph
All Implemented Interfaces:
FlyweightPrototype<ImmutableGraph>
public class UnionArcLabelledImmutableGraph
extends ArcLabelledImmutableGraph
An arc-labelled immutable graph representing the union of two given such graphs. Here by “union” we mean that an arc will belong to the union iff it belongs to at least one of the two graphs (the number of nodes of the union is taken to be the maximum among the number of nodes of each graph). Labels are assumed to have the same prototype in both graphs, and are treated as follows: if an arc is present in but one graph, its label in the resulting graph is going to be the label of the arc in the graph where it comes from; if an arc is present in both graphs, the labels are combined using a provided LabelMergeStrategy.

Remarks about the implementation

Due to the lack of multiple inheritance, we could not extend both UnionImmutableGraph and ArcLabelledImmutableGraph, hence we forcedly decided to extend the latter. The possibility of using delegation on the former was also discarded because the code for reading and merging labels is so tightly coupled with the rest that it would have been essentially useless (and even dangerous) to delegate the iteration methods. As a result, some of the code of this class is actually almost a duplicate of the code of UnionImmutableGraph.

  • Constructor Details

    • UnionArcLabelledImmutableGraph

      public UnionArcLabelledImmutableGraph​(ArcLabelledImmutableGraph g0, ArcLabelledImmutableGraph g1, LabelMergeStrategy labelMergeStrategy)
      Creates the union of two given graphs.
      Parameters:
      g0 - the first graph.
      g1 - the second graph.
      labelMergeStrategy - the strategy used to merge labels when the same arc is present in both graphs.

  • Method Details

    • copy

      public UnionArcLabelledImmutableGraph copy()
      Description copied from class: ImmutableGraph
      Returns a flyweight copy of this immutable graph.
      Specified by:
      copy in interface FlyweightPrototype<ImmutableGraph>
      Specified by:
      copy in class ArcLabelledImmutableGraph
      Returns:
      a flyweight copy of this immutable graph.
      See Also:
      FlyweightPrototype

    • nodeIterator

      public ArcLabelledNodeIterator nodeIterator​(int from)
      Description copied from class: ArcLabelledImmutableGraph
      Returns a node iterator for scanning the graph sequentially, starting from the given node.
      Overrides:
      nodeIterator in class ArcLabelledImmutableGraph
      Parameters:
      from - the node from which the iterator will iterate.
      Returns:
      an ArcLabelledNodeIterator for accessing nodes, successors and their labels sequentially.
      See Also:
      ImmutableGraph.nodeIterator()

    • numNodes

      public int numNodes()
      Description copied from class: ImmutableGraph
      Returns the number of nodes of this graph.

      Albeit this method is not optional, it is allowed that this method throws an UnsupportedOperationException if this graph has never been entirely traversed using a node iterator. This apparently bizarre behaviour is necessary to support implementations as ArcListASCIIGraph, which do not know the actual number of nodes until a traversal has been completed.

      Specified by:
      numNodes in class ImmutableGraph
      Returns:
      the number of nodes.

    • randomAccess

      public boolean randomAccess()
      Description copied from class: ImmutableGraph
      Checks whether this graph provides random access to successor lists.
      Specified by:
      randomAccess in class ImmutableGraph
      Returns:
      true if this graph provides random access to successor lists.

    • hasCopiableIterators

      public boolean hasCopiableIterators()
      Description copied from class: ImmutableGraph
      Whether the node iterators returned by this graph support NodeIterator.copy(int).
      Overrides:
      hasCopiableIterators in class ImmutableGraph
      Returns:
      true if this graph provides copiable iterators.

    • successorArray

      public int[] successorArray​(int x)
      Description copied from class: ImmutableGraph
      Returns a reference to an array containing the successors of a given node.

      The returned array may contain more entries than the outdegree of x. However, only those with indices from 0 (inclusive) to the outdegree of x (exclusive) contain valid data.

      Overrides:
      successorArray in class ImmutableGraph
      Parameters:
      x - a node.
      Returns:
      an array whose first elements are the successors of the node; the array must not be modified by the caller.

    • outdegree

      public int outdegree​(int x)
      Description copied from class: ImmutableGraph
      Returns the outdegree of a node.
      Specified by:
      outdegree in class ImmutableGraph
      Parameters:
      x - a node.
      Returns:
      the outdegree of the given node.

    • labelArray

      public Label[] labelArray​(int x)
      Description copied from class: ArcLabelledImmutableGraph
      Returns a reference to an array containing the labels of the arcs going out of a given node in the same order as the order in which the corresponding successors are returned by ArcLabelledImmutableGraph.successors(int).

      The returned array may contain more entries than the outdegree of x. However, only those with indices from 0 (inclusive) to the outdegree of x (exclusive) contain valid data.

      Overrides:
      labelArray in class ArcLabelledImmutableGraph
      Returns:
      an array whose first elements are the labels of the arcs going out of x; the array must not be modified by the caller.

    • successors

      public ArcLabelledNodeIterator.LabelledArcIterator successors​(int x)
      Description copied from class: ImmutableGraph
      Returns a lazy iterator over the successors of a given node. The iteration terminates when -1 is returned.
      Specified by:
      successors in class ArcLabelledImmutableGraph
      Parameters:
      x - a node.
      Returns:
      a lazy iterator over the successors of the node.

    • prototype

      public Label prototype()
      Description copied from class: ArcLabelledImmutableGraph
      Returns a prototype of the labels used by this graph. The prototype can be used to produce new copies, but must not be modified by the caller.
      Specified by:
      prototype in class ArcLabelledImmutableGraph
      Returns:
      a prototype for the labels of this graph.