Class ImmutableDirectedGraphAdapter

  • All Implemented Interfaces:
    it.unimi.dsi.lang.FlyweightPrototype<ImmutableDirectedGraphAdapter>, Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>

    public class ImmutableDirectedGraphAdapter
    extends AbstractImmutableGraphAdapter<it.unimi.dsi.fastutil.ints.IntIntPair>
    implements it.unimi.dsi.lang.FlyweightPrototype<ImmutableDirectedGraphAdapter>
    An adapter class for directed graphs using WebGraph's ImmutableGraph.

    Nodes are instances of Integer corresponding to the index of a node in WebGraph. Edges are represented by an IntIntPair. The left and right element are the source and the target of the edge. Since the underlying graph is immutable, the resulting graph is unmodifiable. Edges are immutable and can be tested for equality (e.g., stored in a dictionary).

    WebGraph provides methods for successors only, so to adapt a directed graph you must provide both a graph and its transpose (methods to compute the transpose are available in Transform). You need to load an ImmutableGraph and its transpose using one of the available load methods, and then build an adapter:

     immutableGraph = ImmutableGraph.loadMapped("mygraph");
     immutableTranspose = ImmutableGraph.loadMapped("mygraph-t");
     adapter = new ImmutableDirectedGraphAdapter(immutableGraph, immutableTranspose);
     

    The first graph will be used to implement outgoingEdgesOf(Integer), and the second graph to implement incomingEdgesOf(Integer). It is your responsibility that the two provided graphs are one the transpose of the other (for each arc x → y in a graph there must be an arc y → x in the other, and vice versa). No check will be performed. Note that computing the number of edges of a graph requires a full scan of the edge set if ImmutableGraph.numArcs() is not supported (the first time—then it will be cached).

    If you use a load method that does not provide random access, most methods will throw an UnsupportedOperationException.

    If you know that you will never used methods based on incoming edges (incomingEdgesOf(Integer), inDegreeOf(Integer), edgesOf(Integer), degreeOf(Integer)), you can also use the constructor using just a graph, but all such methods will throw a NullPointerException:

     immutableGraph = ImmutableGraph.loadMapped("mygraph");
     adapter = new ImmutableDirectedGraphAdapter(immutableGraph);
     

    If necessary, you can adapt a big WebGraph graph with at most Integer.MAX_VALUE vertices using the suitable wrapper.

    Thread safety

    This class is not thread safe: following the FlyweightPrototype pattern, users can access concurrently the graph by getting lightweight copies.

    Fast adjacency check

    As it happens for the sparse representation of JGraphT, usually a WebGraph compressed representation requires scanning the adjacency list of a node to test whether a specific arc exists. However, if you adapt a WebGraph class (such as EFGraph) which provides skippable iterators with fast skipping, adjacency can be tested more quickly (e.g., essentially in constant time in the case of EFGraph).

    Author:
    Sebastiano Vigna
    See Also:
    AbstractImmutableBigGraphAdapter
    • Constructor Detail

      • ImmutableDirectedGraphAdapter

        public ImmutableDirectedGraphAdapter​(it.unimi.dsi.webgraph.ImmutableGraph immutableGraph,
                                             it.unimi.dsi.webgraph.ImmutableGraph immutableTranspose)
        Creates an adapter for a directed immutable graph.

        It is responsibility of the caller that the two provided graphs are one the transpose of the other (for each arc x → y in a graph there must be an arc y → x in the other). If this property is not true, results will be unpredictable.

        Parameters:
        immutableGraph - an immutable graph.
        immutableTranspose - its transpose.
      • ImmutableDirectedGraphAdapter

        public ImmutableDirectedGraphAdapter​(it.unimi.dsi.webgraph.ImmutableGraph immutableGraph)
        Creates an adapter for a directed immutable graph implementing only methods based on outgoing edges.
        Parameters:
        immutableGraph - an immutable graph.
    • Method Detail

      • makeEdge

        protected it.unimi.dsi.fastutil.ints.IntIntPair makeEdge​(int x,
                                                                 int y)
        Specified by:
        makeEdge in class AbstractImmutableGraphAdapter<it.unimi.dsi.fastutil.ints.IntIntPair>
      • containsEdge

        public boolean containsEdge​(it.unimi.dsi.fastutil.ints.IntIntPair e)
        Description copied from interface: Graph
        Returns true if this graph contains the specified edge. More formally, returns true if and only if this graph contains an edge e2 such that e.equals(e2). If the specified edge is null returns false.
        Specified by:
        containsEdge in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        e - edge whose presence in this graph is to be tested.
        Returns:
        true if this graph contains the specified edge.
      • edgeSet

        public java.util.Set<it.unimi.dsi.fastutil.ints.IntIntPair> edgeSet()
        Description copied from interface: Graph
        Returns a set of the edges contained in this graph. The set is backed by the graph, so changes to the graph are reflected in the set. If the graph is modified while an iteration over the set is in progress, the results of the iteration are undefined.

        The graph implementation may maintain a particular set ordering (e.g. via LinkedHashSet) for deterministic iteration, but this is not required. It is the responsibility of callers who rely on this behavior to only use graph implementations which support it.

        Specified by:
        edgeSet in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Returns:
        a set of the edges contained in this graph.
      • degreeOf

        public int degreeOf​(java.lang.Integer vertex)
        Description copied from interface: Graph
        Returns the degree of the specified vertex.

        A degree of a vertex in an undirected graph is the number of edges touching that vertex. Edges with same source and target vertices (self-loops) are counted twice.

        In directed graphs this method returns the sum of the "in degree" and the "out degree".

        Specified by:
        degreeOf in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        vertex - vertex whose degree is to be calculated.
        Returns:
        the degree of the specified vertex.
      • edgesOf

        public java.util.Set<it.unimi.dsi.fastutil.ints.IntIntPair> edgesOf​(java.lang.Integer vertex)
        Description copied from interface: Graph
        Returns a set of all edges touching the specified vertex. If no edges are touching the specified vertex returns an empty set.
        Specified by:
        edgesOf in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        vertex - the vertex for which a set of touching edges is to be returned.
        Returns:
        a set of all edges touching the specified vertex.
      • inDegreeOf

        public int inDegreeOf​(java.lang.Integer vertex)
        Description copied from interface: Graph
        Returns the "in degree" of the specified vertex.

        The "in degree" of a vertex in a directed graph is the number of inward directed edges from that vertex. See http://mathworld.wolfram.com/Indegree.html.

        In the case of undirected graphs this method returns the number of edges touching the vertex. Edges with same source and target vertices (self-loops) are counted twice.

        Specified by:
        inDegreeOf in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        vertex - vertex whose degree is to be calculated.
        Returns:
        the degree of the specified vertex.
      • incomingEdgesOf

        public java.util.Set<it.unimi.dsi.fastutil.ints.IntIntPair> incomingEdgesOf​(java.lang.Integer vertex)
        Description copied from interface: Graph
        Returns a set of all edges incoming into the specified vertex.

        In the case of undirected graphs this method returns all edges touching the vertex, thus, some of the returned edges may have their source and target vertices in the opposite order.

        Specified by:
        incomingEdgesOf in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        vertex - the vertex for which the list of incoming edges to be returned.
        Returns:
        a set of all edges incoming into the specified vertex.
      • outDegreeOf

        public int outDegreeOf​(java.lang.Integer vertex)
        Description copied from interface: Graph
        Returns the "out degree" of the specified vertex.

        The "out degree" of a vertex in a directed graph is the number of outward directed edges from that vertex. See http://mathworld.wolfram.com/Outdegree.html.

        In the case of undirected graphs this method returns the number of edges touching the vertex. Edges with same source and target vertices (self-loops) are counted twice.

        Specified by:
        outDegreeOf in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        vertex - vertex whose degree is to be calculated.
        Returns:
        the degree of the specified vertex.
      • outgoingEdgesOf

        public java.util.Set<it.unimi.dsi.fastutil.ints.IntIntPair> outgoingEdgesOf​(java.lang.Integer vertex)
        Description copied from interface: Graph
        Returns a set of all edges outgoing from the specified vertex.

        In the case of undirected graphs this method returns all edges touching the vertex, thus, some of the returned edges may have their source and target vertices in the opposite order.

        Specified by:
        outgoingEdgesOf in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Parameters:
        vertex - the vertex for which the list of outgoing edges to be returned.
        Returns:
        a set of all edges outgoing from the specified vertex.
      • getType

        public GraphType getType()
        Description copied from interface: Graph
        Get the graph type. The graph type can be used to query for additional metadata such as whether the graph supports directed or undirected edges, self-loops, multiple (parallel) edges, weights, etc.
        Specified by:
        getType in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Returns:
        the graph type
      • iterables

        public GraphIterables<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair> iterables()
        Description copied from interface: Graph
        Access the graph using the GraphIterables interface. This allows accessing graphs without the restrictions imposed by 32-bit arithmetic. Moreover, graph implementations are free to implement this interface without explicitly materializing intermediate results.
        Specified by:
        iterables in interface Graph<java.lang.Integer,​it.unimi.dsi.fastutil.ints.IntIntPair>
        Returns:
        the graph iterables