using System;

using System.Collections.Generic;

using System.Linq;

using System.Xml.Linq;

​

public class Program

{

    public static void Main(string[] args)

    {

        const string xml =

@"<root>

   <row>

    <id>0001</id>

    <type>credit</type>

    <investment>1000</investment>

    <ppr>0.83</ppr>

    <candidate>

        <id>5001</id>

        <name>Hugo</name>

    </candidate>

    <candidate>

        <id>5002</id>

        <name>Jack</name>

    </candidate>

    <candidate>

        <id>5005</id>

        <name>Kate</name>

    </candidate>

  </row>

</root>";

​

        var original = XDocument.Parse(xml);

        var grouped = new XDocument(GroupElements(original.Elements()));

​

        Console.WriteLine(grouped);

    }

​

    private static IEnumerable<XElement> GroupElements(IEnumerable<XElement> elements)

    {

        var elementsByName = elements.GroupBy(x => x.Name);

​

        foreach (var grouping in elementsByName)

        {

            var transformed = grouping.Select(e =>

                new XElement(e.Name,

                    GroupElements(e.Elements()),

                    e.Attributes(),

                    e.Nodes().OfType<XText>()));

            if (grouping.Count() == 1)

            {

                yield return transformed.Single();

            }

            else

            {

                var groupName = grouping.Key + "s";

                yield return new XElement(groupName, transformed);

            }

        }

    }

}

​

​

​