Question

I have a List<> which contains another List<>

I need to find if a given value is present in any of the items in the innermost list.
If match found, I need that specific item and return.

I am doing this as shown below:

InnerList inner = null;
foreach(TopList in topListItems)
{
    inner = asn.Owners.Find(x => x.GuestId == guestId);
    if(inner != null)
         break;
}

//item found if inner is not null
//else item absent in the inner list

Any other alternate way that may run faster than this?

EDIT:
Some correction: I just need to see if inner list has an item with a specific value.
If yes, then I need to return the top level item that that has the match.
I guess the logic is the same.

Answer 1

If you want to keep the data structure then the only improvement I see is throwing out the delegate based search and search manually. I expect an improvement of about factor two with that.

foreach(var innerList in outerList)
{
    foreach(var item in innerList)
    {
        if(item.GuestId == guestId)
            return innerList;
    }
}
return null;

If possible you could employ dictionaries in some way. But I don’t know enough about your problem to tell you if that’s possible. This can give a really big speedup since a search by key in a dictionary is O(1) and not just O(n).

In some situations a for loop might give a slight speedup over the foreach loop, but I don’t know if this is one of them. So you’ll need to benchmark.