// Use ElementLevel filter to find elements by their associated level in the document

// Find the level whose Name is "Level 1"
FilteredElementCollector collector = new FilteredElementCollector(document);
ICollection<Element> levels = collector.OfClass(typeof(Level)).ToElements();
var query = from element in collector where element.Name == "Level 1" select element;// Linq query

// Get the level id which will be used to match elements
List<Element> level1 = query.ToList<Element>();
ElementId levelId = level1[0].Id;

// Find all walls on level one
ElementLevelFilter level1Filter = new ElementLevelFilter(levelId);
collector = new FilteredElementCollector(document);
ICollection<Element> allWallsOnLevel1 = collector.OfClass(typeof(Wall)).WherePasses(level1Filter).ToElements();


// Find all rooms not on level one: use an inverted ElementLevelFilter to match all elements not on the target level
ElementLevelFilter notOnLevel1Filter = new ElementLevelFilter(levelId, true); // Inverted filter
collector = new FilteredElementCollector(document);
IList<Element> allRoomsNotOnLevel1 = collector.WherePasses(new RoomFilter()).WherePasses(notOnLevel1Filter).ToElements();

' Use ElementLevel filter to find elements by their associated level in the document


' Find the level whose Name is "Level 1"
Dim collector As New FilteredElementCollector(document)
Dim levels As ICollection(Of Element) = collector.OfClass(GetType(Level)).ToElements()
Dim query As System.Collections.Generic.IEnumerable(Of Autodesk.Revit.DB.Element)
query = From element In collector _
 Where element.Name = "Level 1" _
 Select element

' Linq query
' Get the level id which will be used to match elements
Dim level1 As List(Of Element) = query.ToList()
Dim levelId As ElementId = level1(0).Id

' Find all walls on level one
Dim level1Filter As New ElementLevelFilter(levelId)
collector = New FilteredElementCollector(document)
Dim allWallsOnLevel1 As ICollection(Of Element) = collector.OfClass(GetType(Wall)).WherePasses(level1Filter).ToElements()


' Find all rooms not on level one: use an inverted ElementLevelFilter to match all elements not on the target level
Dim notOnLevel1Filter As New ElementLevelFilter(levelId, True)
' Inverted filter
collector = New FilteredElementCollector(document)
Dim allRoomsNotOnLevel1 As IList(Of Element) = collector.WherePasses(New RoomFilter()).WherePasses(notOnLevel1Filter).ToElements()