How to group these XDocuments?

Question

Problem

I have a collection of instances XDocument. Each document has a repeating element that can take on a different meaning. I want to group them by this value, but each element can specify a different value.

<sampledoc>
  <value>a</value>
  <value>b</value>
  <value>c</value>
</sampledoc>

Example

• Document A has the values ​​a, b, c
• Document B has values ​​b, c, d
• Document C has values ​​a, b

I need a group that:

• group a
  • Document A
  • Document C
• group b
  • Document A
  • Document B
  • Document C
• group c
  • Document A
  • Document B
• group d
  • Document B

Question

I am sure I have to do this, but right now I do not see a tree for trees.

docs.GroupBy... ( ), , , , . , LINQ , , .

GroupBy AsLookup LINQ? ?

#, - .

Update

, :

// Collate all the different values
docs.SelectMany(doc => doc.Elements("Value")
                          .Select(el => el.Value))
    // Remove duplicate values
    .Distinct()
    // Generate a lookup of specific value to all
    // documents that contain that value
    .ToLookup(v => v, v => docs.Where(doc => doc.Elements("Value")
                                                .Any(el=>el.Value == v)));

Answer 1

GroupBy , .

var docs = new XDocument[] { docA, docB, docC } ;
var result = docs
   .SelectMany(doc => doc.Root.Elements("Value"))
   .Select(el => el.Value)
   .Distinct()
   .Select(key => new {
        Key = key,
        Documents = docs.Where(doc =>
            doc.Root.Elements("Value").Any(el => el.Value == key))
   });