How to group XML data by multiple value

Question

I need to group "Document" value from XML. Problem is because key value (productType) can be multiple.

This is XML:

<Documents>
<Document>
    <id>1</id>
    <title>title1</title>
    <productTypes>
        <productType id="x1">Capital Costs Analysis Forum - Brazil</productType>
  <productType id="x3">Environmental, Health and Safety &amp; Sustainability</productType>
    </productTypes>
</Document>
<Document>
    <id>2</id>
    <title>title2</title>
    <productTypes>
  <productType id="x1">Capital Costs Analysis Forum - Brazil</productType>
    </productTypes>
</Document>
<Document>
    <id>3</id>
    <title>title3</title>
    <productTypes>
  <productType id="x3">Environmental, Health and Safety &amp; Sustainability</productType>
    </productTypes>
</Document>
<Document>
    <id>4</id>
    <title>title4</title>
    <productTypes>
        <productType id="x2">Defense, Risk &amp; Security</productType>
    </productTypes>
</Document>

And this is what I try:

var documents = from document in some.Descendants("Document")
                group document by (string)document
                    .Element("productTypes")
                    .Elements("productType")
                    .First() into docGroup
select docGroup;

My code is working only if is there one productType element. How to change my code to work if there is multiple value of productType?

Answer 1

You did not explain what result you want but I suspect you want the following grouping:

        var documentGroups = 
            from document in XDocument.Load("input.xml").Descendants("Document")
            from productType in document.Element("productTypes").Elements("productType")
            group document by (string)productType.Attribute("id");

        foreach (var documentGroup in documentGroups)
        {
            Console.WriteLine("Group {0} has the following members:", documentGroup.Key);
            foreach (XElement document in documentGroup)
            {
                Console.WriteLine("\t{0}", (string)document.Element("title"));
            }
            Console.WriteLine();
        }

With the input being

<Documents>
  <Document>
    <id>1</id>
    <title>title1</title>
    <productTypes>
      <productType id="x1">Capital Costs Analysis Forum - Brazil</productType>
      <productType id="x3">Environmental, Health and Safety &amp; Sustainability</productType>
    </productTypes>
  </Document>
  <Document>
    <id>2</id>
    <title>title2</title>
    <productTypes>
      <productType id="x1">Capital Costs Analysis Forum - Brazil</productType>
    </productTypes>
  </Document>
  <Document>
    <id>3</id>
    <title>title3</title>
    <productTypes>
      <productType id="x3">Environmental, Health and Safety &amp; Sustainability</productType>
    </productTypes>
  </Document>
  <Document>
    <id>4</id>
    <title>title4</title>
    <productTypes>
      <productType id="x2">Defense, Risk &amp; Security</productType>
    </productTypes>
  </Document>
</Documents>

that outputs

Group x1 has the following members:
        title1
        title2

Group x3 has the following members:
        title1
        title3

Group x2 has the following members:
        title4