Package com.jgalgo.io

Class DimacsGraphReader

  • All Implemented Interfaces:
    GraphReader<Integer,​Integer>
    public final class DimacsGraphReader
extends Object
    Read a graph in 'DIMACS' format.

    The DIMACS format is the graph format used by the 'Center of Discrete Mathematics and Theoretical Computer Science' for their graph challenges. There are many sub-formats, but the most common are the 'edge' and 'sp' formats, which are supported by this class. A DIMACS file contains a short header which specify the sub-format along with the number of edges and vertices, followed by the edges themselves. The edges are specified by a pair of vertices, and in the 'sp' format, also by a weight. The vertices are numbered from 1 to n, where n is the number of vertices, and similarly the edges are numbered from 1 to m, where m is the number of edges. Only undirected graphs are supported by this format.

    The 'edge' format is the simplest, and is used for unweighted undirected graphs. An example file is: 

     c this is a comment
 c this is the graph with vertices {1,2,3,4,5} and edges {1=(1,2),2=(2,3),3=(2,4),4=(3,4),5=(4,5)}
 p edge 5 5
 e 1 2
 e 2 3
 e 2 4
 e 3 4
 e 4 5

    The 'sp' format is used for (integer) weighted undirected graphs. An example file is: 

     c this is a comment
 c this is the graph with vertices {1,2,3,4,5} and edges {1=(1,2),2=(2,3),3=(2,4),4=(3,4),5=(4,5)}
 c the weights of the edges are {1=5,2=13,3=2,4=-7,5=0}
 p sp 5 5
 e 1 2 3
 e 2 3 13
 e 2 4 2
 e 3 4 -7
 e 4 5 0

    The reader will identify the format automatically by looking at the header of the file. If the format contains edge weights ('sp' format), the built graph will have edges integer weights keys by "weight", or a key chosen by the user using setEdgeWeightsKey(String). See Graph.edgesWeights(String).

    Author:
    Barak Ugav
    See Also:
    DIMACS Graph Format, DimacsGraphWriter

    • Constructor Detail

      • DimacsGraphReader

        public DimacsGraphReader()
        Create a new reader.

    • Method Detail

      • setEdgeWeightsKey

        public void setEdgeWeightsKey​(String weightsKey)
        Sets the key of the edge weights that will be read.

        When the reader reads a graph in the 'sp' format a WeightsInt weights will be added to the built graph. By default, the weights will be added with key "weight". Use this method to specify a different key.

        Parameters:
        weightsKey - the key of the edge weights that will be read
        See Also:
        Graph.edgesWeights(String)

      • readGraph

        public IntGraph readGraph​(Reader reader)
        Description copied from interface: GraphReader
        Read a graph from an I/O reader.
        Parameters:
        reader - an I/O reader that contain a graph description
        Returns:
        a new graph read from the reader

      • readGraph

        public IntGraph readGraph​(File file)
        Description copied from interface: GraphReader
        Read a graph from a file.
        Parameters:
        file - a file that contain a graph description
        Returns:
        a new graph read from the file

      • readGraph

        public IntGraph readGraph​(String path)
        Description copied from interface: GraphReader
        Read a graph from a file, given a path to it.
        Parameters:
        path - a path to a file that contain a graph description
        Returns:
        a new graph read from the file