Find an element in List of List, c#

Question

I have a list of lists as below:

List<List <T> > userList

Class T { string uniqueidentifier, string param2, int param2}

I have a uniqueidentifier and i need to find the element T in the list that has the same 'uniqueidentifier' value.

I can do it using two 'foreach' loops. This does not seem to be nice way doing things. I guess there should be some inbuilt method like 'Find' that does the same thing and is highly optimized.

Answer 1

Find is not optimized at all -- it performs a linear search, since that's the only thing that makes sense on an unsorted list. If you are looking at a nicer way to write it, you could use LINQ:

var element = (from sublist in userList
               from item in sublist
               where item.uniqueidentifier == someid
               select item).FirstOrDefault();

Answer 2

Without indexing/hashing a "highly optimized" find won't help. Your best bet is change the storage method of your data, such as a tree.

Without changing the storage mechanism, if you are on a multi-core system parallelize the search.

Answer 3

I would suggest you change the outer list to a Dictionary, then you can find the inner list with its unique identifier.

     Dictionary<string, List<T>> myDictionary = new Dictionary<string,List<T>>();
     myDictionary["1"] = innerList;
     List<T> list = myDictionary["1"]; //find list with unique id "1"

Answer 4

Try this:

var query =
    from ts in userList
    from t in ts
    where t.uniqueidentifier == uniqueidentifier
    select t;

var user = query.FirstOrDefault();