Compare List and return matches in c#

Question

What is the fastest and best way to compare 2 lists and return a match. Only one match is possible. List1 contains dynamic data from a database.

The way I do it now :

foreach (var item1 in List1)
{
   foreach (var item2 in List2 )
   {
       if(item2 == item1)
       string match = item1;
   }
}

I have a feeling like it can be done a lot faster.

Answer 1

Use Enumerable.Intersect.

var matchItem = List1.Intersect(List2).First();

Not really sure how much it is faster to your current code, you can measure it using Stopwatch. But in your current code you should break your inner as well as outer loop on finding the match. Something like:

foreach (var item1 in List1)
{
    string match = null;
    foreach (var item2 in List2)
    {
        if (item2 == item1)
        {
            match = item1;
            break;
        }
    }
    if (match != null)
        break;
}