MatrixMarketReader.cs

using Antlr4.Runtime;
using SparseTransform.DataStructures;
using SparseTransform.Convert;

namespace SparseTransform.Convert
{
    /// <summary>
    /// Provides an IReader implementation to read a MatrixMarket string.
    /// </summary>
    public class MatrixMarketReader : IReader
    {
        public IGraph ReadGraph(String matrix)
        {
            String[] lines = matrix.Split(
            new String[] { "\r\n", "\r", "\n" },
            StringSplitOptions.None
            );

            checkComments(lines);

            if (checkHeader(lines[0]))
            {
                BipartiteGraph graph = new BipartiteGraph();
                ReadContent(lines, (i, j, value) => {
                    graph.AddEdge(i, j);
                });
                return graph;
            }
            else
            {
                AdjacencyGraph graph = new AdjacencyGraph();
                ReadContent(lines, (i, j, value) => {
                    graph.AddEdge(i, j);
                });
                return graph;
            }
        }

        public DoubleMatrix ReadMatrix(String matrix)
        {
            String[] lines = matrix.Split(
            new String[] { "\r\n", "\r", "\n" },
            StringSplitOptions.None
            );

            checkComments(lines);

            String dimLine = lines[getFirstDataLine(lines)];
            String[] dimensions = dimLine.Split(" ");
            DoubleMatrix mat = new DoubleMatrix(Int32.Parse(dimensions[0]), Int32.Parse(dimensions[1]));
            ReadContent(lines, (i, j, value) =>
            {
                mat[i - 1, j - 1] = value;
            });
            return mat;
        }

        /// <summary>
        /// checks with ANTLR4.0 whether the header is a valid instance. The header grammar can be found in the file MMFHeader.g4 
        /// </summary>
        /// <param name="header">header of the MMF-input</param>
        /// <returns>true if matrix is not symmetric</returns>
        private bool checkHeader(String header)
        {
            AntlrInputStream stream = new AntlrInputStream(header);
            MMFHeaderLexer lexer = new MMFHeaderLexer(stream);
            CommonTokenStream commonTokenStream = new CommonTokenStream(lexer);
            MMFHeaderParser speakParser = new MMFHeaderParser(commonTokenStream);
            EListener errorHandler = new EListener();
            speakParser.AddErrorListener(errorHandler);
            VisitorHeader visitor = new VisitorHeader();
            return visitor.Visit(speakParser.header());
        }

       /// <summary>
       /// checks whether the comment-section is valid.
       /// </summary>
       /// <param name="lines">entire input split by newlines</param>
       /// <exception cref="FormatException"></exception>
        private void checkComments(String[] lines)
        {
            bool leftComments = false;
            foreach (String line in lines)
            {
                if (line != "")
                {
                    if (leftComments && line.StartsWith('%'))
                    {
                        throw new FormatException("Syntax Error in MatrixMarket file: Encountered more comments in between data lines.");
                    }
                    else
                    {
                        if (!line.StartsWith('%'))
                        {
                            leftComments = true;
                        }
                    }
                }
                else
                {
                    leftComments = true;
                }
            }
        }

        /// <summary>
        /// creates a graph from the data-section of the MMF-input and meanwhile checks whether the data-section is valid
        /// </summary>
        /// <param name="matrix"></param>
        /// <param name="graph"></param>
        /// <returns></returns>
        /// <exception cref="Exception"></exception>
        public void ReadContent(String[] matrix, Action<int, int, double> processor)
        {
            String[] values;
            int lineCount = getFirstDataLine(matrix);
            matrix[lineCount] = "% " + matrix[lineCount];
            foreach (String line in matrix)
            {
                if (line != "")
                {
                    if (!line.StartsWith('%'))
                    {

                        values = line.Split(" ");
                        if (values.Length != 3)
                        {
                            throw new ArgumentException("Syntax Error in MatrixMarket file: Data line did not contain three elements.");
                        }
                        int i = Int32.Parse(values[0]);
                        int j = Int32.Parse(values[1]);
                        processor(i, j, Double.Parse(values[2]));
                    }
                }
            }
        }

        /// <summary>
        /// computes the first data-line in the MMF-input 
        /// </summary>
        /// <param name="lines"></param>
        /// <returns></returns>
        private int getFirstDataLine(String[] lines)
        {
            int firstDataLine = 0;
            foreach (String line in lines)
            {
                if (line != "")
                {
                    if (line[0] != '%')
                    {
                        break;
                    }
                    else
                    {
                        firstDataLine++;
                    }
                }
                else
                {
                    firstDataLine++;
                }
            }
            return firstDataLine;
        }
    }
}