Question

I have two List<string> (listOfFullPaths containg full database paths for e.g. “C:\MyDir\SomeDir\SomeDatabase.mdf”) and some other List<string> containing some of the names of the databases (only) (‘listOfDatabases’). So each might include

List<string> listOfFullPaths = new List<string>() 
{
    "C:\MyDir\SomeDir\SomeDatabase1.mdf",
    "C:\MyDir\SomeDir\SomeDatabase2.mdf",
    "C:\MyDir\SomeDir\SomeDatabase3.mdf"
};

the other just

List<string> listOfFullPaths = new List<string>() 
{
    "SomeDatabase1",
    "SomeDatabase2"
};

My question is what is the most efficent way of returning the full paths contined in listOfFullPaths that have their corresponding database in listOfDatabases?

Note: The answer is not something like

List<string> tmpList = new List<string>();
foreach (string database in listOfDatabases)
    if (listOfFullPaths.Contains(database))
        tmpList.Add(database);
listOfFullPaths.Clear();
listOfFullPaths = tmpList;

although this does what I want.

Answer 1

If you want to do it efficiently in terms of speed (i.e. in O(n)) then JaredPar’s answer is correct.
Here is a more idiomatic version:

var set = new HashSet<string>(listOfDbs);
List<string> result = listOfFullPaths
    .Where(p => set.Contains(Path.GetFileNameWithoutExtension(p)))
    .ToList();