How to find consecutive nodes with consecutive attribute values using XDocument or XElement?

Question

How do I check a xml file for consecutive nodes(set apart by a comma and a space) that contain an attribute whose integer portion of the value is incremented by +1 and write the matched(if any) string to a file using XDocument or XElement methods? Here is a sample xml file

<?xml version="1.0"?>
<catalog>
   <book id="bk101">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth <chk att="sdf1">A-list</chk>, <chk att="sdf2">B-list</chk>, <chk att="sdf3">X-list</chk> look at creating applications 
      with XML.</description>
   </book>
   <book id="bk102">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former <chk att="sdf14">lA-list</chk>, <chk att="sdf16">pB-list</chk>, <chk att="sdf3">sX-list</chk> architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
   <book id="bk103">
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-11-17</publish_date>
      <description>After the collapse <chk att="sdf11">A-list</chk>, <chk att="sdf20">B-list</chk>, <chk att="sdf21">X-list</chk>, <chk att="sdf22">A-list</chk>, <chk att="sdf23">B-list</chk>, <chk att="sdf25">X-list</chk> of a nanotechnology 
      society in England, the young survivors lay the 
      foundation for a new society.</description>
   </book>
</catalog>

I want to extract the strings

<chk att="sdf1">A-list</chk>, <chk att="sdf2">B-list</chk>, <chk att="sdf3">X-list</chk>

and

<chk att="sdf20">B-list</chk>, <chk att="sdf21">X-list</chk>, <chk att="sdf22">A-list</chk>, <chk att="sdf23">B-list</chk>

from the above samle xml file? I thought about using regex find for this but I cannot figure out a way to add the incrementing attribute value...

How can I do that?

Answer 1

Here's a way to do it,

Note that there is no error checking and it's pretty condensed, you will want to improve on both aspects robustness and clarity.

using System;
using System.Linq;
using System.Text.RegularExpressions;
using System.Xml.Linq;

namespace ConsoleApp1
{
    internal static class Program
    {
        private const string Text = @"<?xml version=""1.0""?>
<catalog>
   <book id=""bk101"">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth <chk att=""sdf1"">A-list</chk>, <chk att=""sdf2"">B-list</chk>, <chk att=""sdf3"">X-list</chk> look at creating applications 
      with XML.</description>
   </book>
   <book id=""bk102"">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former <chk att=""sdf14"">lA-list</chk>, <chk att=""sdf16"">pB-list</chk>, <chk att=""sdf3"">sX-list</chk> architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
   <book id=""bk103"">
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-11-17</publish_date>
      <description>After the collapse <chk att=""sdf11"">A-list</chk>, <chk att=""sdf20"">B-list</chk>, <chk att=""sdf21"">X-list</chk>, <chk att=""sdf22"">A-list</chk>, <chk att=""sdf23"">B-list</chk>, <chk att=""sdf25"">X-list</chk> of a nanotechnology 
      society in England, the young survivors lay the 
      foundation for a new society.</description>
   </book>
</catalog>
";

        private static void Main(string[] args)
        {
            var document = XDocument.Parse(Text);

            var books = document.Element("catalog").Elements("book");

            foreach (var book in books)
            {
                var attributes = book.Element("description").Elements("chk").Attributes("att");

                var values = attributes.Select(s => int.Parse(Regex.Match(s.Value, @"\d+").Value)).ToArray();

                var first = values.First();
                var last = values.Last();
                var sum = Enumerable.Range(first, Math.Max(0, last - first + 1)).ToArray().Sum();

                var consecutive = values.Sum() == sum;

                Console.WriteLine(consecutive);
            }
        }
    }
}

Result:

True
False
False