Identify Point in Matrix Subrange

Make/O/N=(5,5) mat = p + 10*q
Display mat[][2]    // Display all rows of column 2

Display mat[][2]        // All rows of one column
Display mat[1,3][2]     // Range of rows of one column
Display mat[0,4;2][2]       // Range of rows of one column with increment
Display mat[2][]        // All columns of one row
Display mat[2][1,3]     // Range of columns of one row
Display mat[2][0,4;2]       // Range of columns of one row with increment

// GetMatrixTraceIndices(graphName, traceName, dataIndex, wantY, matrixRow, matrixColumn)
//
// traceName is the name of a trace whose X or Y coordinates come from a (matrix) 2D wave.
//
// dataIndex is the row index (when displaying a column of a matrix) or the column index
// (when displaying a column of a matrix) of the matrix element supplying the data
// for a point in the trace. This is the value returned by pcsr(<cursor>) when the
// specified <cursor> is on the an element of the trace.
//
// Returns via matrixRow and matrixColumn the indices of the specified point in the matrix.
//
// The function result is zero if everything went right or non-zero in the event of an error.
//
// Calling this when the trace in question does not come from a matrix returns -1.
// See demo below.
Function GetMatrixTraceIndices(graphName, traceName, dataIndex, wantY, matrixRow, matrixColumn)
    String graphName            // Graph name or "" for top graph
    String traceName            // Trace name, e.g. "mat" or "mat#1"
    Variable wantY              // 0 to get indices for X coordinate, 1 to get indices for Y coordinate
    Variable dataIndex          // See explanation above
    Variable& matrixRow     // Output
    Variable& matrixColumn      // Output
   
    String info = TraceInfo(graphName, traceName, 0)
    if (strlen(info) == 0)
        return -1               // No such trace
    endif
   
    Variable isXY = WaveExists(XWaveRefFromTrace(graphName, traceName))
    if (wantY==0 && !isXY)
        wantY = 1               // This is a waveform plot so X values come from Y wave
    endif
   
    String rangeStr
    if (wantY)
        Wave w = TraceNameToWaveRef(graphName, traceName)
        rangeStr = StringByKey("YRANGE", info)
    else
        Wave w = XWaveRefFromTrace(graphName, traceName)
        rangeStr = StringByKey("XRANGE", info)
    endif
   
    if (WaveDims(w) != 2)
        return -1               // Not a matrix
    endif
   
    String rowStr, columnStr, temp
    String regExp = "(\[)(.*)(\])(\[)(.*)(\])"
    SplitString /E=regExp rangeStr, temp, rowStr, temp, temp, columnStr, temp
    // Print rowStr, columnStr          // For debugging
   
    Variable displayingColumn = 1       // True if trace data comes from matrix column, not matrix row
    if (CmpStr(columnStr,"*") == 0)
        displayingColumn = 0            // e.g., Display mat[2][*]  // Display all columns of row 2
    endif
    if (strsearch(columnStr,",",0) >= 0)
        displayingColumn = 0            // e.g., Display mat[2][1,3]    // Display columns 1 to 3 of row 2
    endif
   
    if (displayingColumn)
        // mat[*][<column>], mat[<firstRow>,<lastRow>][<column>] or mat[<firstRow>,<lastRow>;<increment>][<column>]
        matrixRow = dataIndex
        matrixColumn = str2num(columnStr)
    else                                    // !displayingColumn
        // mat[<row>][*], mat[<row>][<firstColumn>,<lastColumn>] or mat[<row>][<firstColumn>,<lastColumn>;<increment>]
        matrixRow = str2num(rowStr)
        matrixColumn = dataIndex
    endif

    return 0
End