using System;

using System.Collections.Generic;

using System.Text;

using System.Linq;

using System.Xml.Serialization;

using System.Xml;

using System.Xml.XPath;

using System.Xml.Linq;

using System.IO;

using System.Data;

using System.Runtime.Serialization;

using System.Runtime.Serialization.Formatters.Binary;

using System.IO.Compression;

using System.Reflection;

​

using NUnit.Framework; //NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/58998053/how-to-select-element-by-index-in-xpath-net-application

​

    public class TestClass

    {

        public static void Test()

        {

            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(GetXml())))

            {

                XPathDocument xpResDoc = new XPathDocument(stream);

                XPathNavigator xpNav = xpResDoc.CreateNavigator();

                XmlNamespaceManager nsmgr = new XmlNamespaceManager(xpNav.NameTable);

                nsmgr.AddNamespace("g2", "http://schemas.datastream.net/MP_functions/MP0118_GetGridHeaderData_001_Result");

​

                XPathNodeIterator xpNIter = xpNav.Select("//R", nsmgr);

​

                foreach (XPathNavigator nav in xpNIter)

                {

                    Console.WriteLine(nav);

                    /*

                        Now I want to iterate through each R element and use XPATH to select each of the six D nodes by its index position.

                        The order of the D nodes are a known dataset and I want to build a comma separated string by concatenating the value of each D node,

                        which will later be appended to a CSV file along with a pre-defined header row.

                    */

​

                    /* I attempted the following XPATH */

                    var nodes = nav.Select("(.//D)[1]").Cast<XPathNavigator>().ToList();

                    Console.WriteLine("   Count = {0}, Result = {1}", nodes.Count, string.Join(",", nodes));

                }           

            }

        }

        static string GetXml()

        {

            return @"<GRID xmlns:dstm=""http://schemas.datastream.net/MP_functions/MP0118_GetGridHeaderData_001_Result"">

  <DATA>

    <R>

      <D>2645</D>

      <D>HJIT.HRE@RGW.COM</D>

      <D>2019-09-27 10:17:36.0</D>

      <D>114041</D>

      <D>Awaiting Planning</D>

      <D>Work Planned</D>

    </R>

    <R>

      <D>2649</D>

      <D>HJIT.HRE@RGW.COM</D>

      <D>2019-09-27 10:33:24.0</D>

      <D>114043</D>

      <D>Awaiting Release</D>

      <D>Awaiting Planning</D>

    </R>

    <R>

      <D>2652</D>

      <D>HJIT.HRE@RGW.COM</D>

      <D>2019-09-27 10:36:53.0</D>

      <D>114041</D>

      <D>Awaiting Planning</D>

      <D>Work Planned</D>

    </R>

  </DATA>

</GRID>";

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.CodeBase.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​