Checking for duplicates in a complex object using Linq or Lambda expression

Question

I've just started learning linq and lambda expressions, and they seem to be a good fit for finding duplicates in a complex object collection, but I'm getting a little confused and hope someone can help put me back on the path to happy coding.

My object is structured like list.list.uniqueCustomerIdentifier

I need to ensure there are no duplicate uniqueCustomerIdentifier with in the entire complex object. If there are duplicates, I need to identify which are duplicated and return a list of the duplicates.

Answer 1

• Unpack the hierarchy
• Project each element to its uniqueID property
• Group these ID's up
• Filter the groups by groups that have more than 1 element
• Project each group to the group's key (back to uniqueID)
• Enumerate the query and store the result in a list.

---

var result = 
  myList
    .SelectMany(x => x.InnerList)
    .Select(y => y.uniqueCustomerIdentifier)
    .GroupBy(id => id)
    .Where(g => g.Skip(1).Any())
    .Select(g => g.Key)
    .ToList()