FindElement and Collector Optimisation

As I recently mentioned, Mikako Harada published a very nice article on programmatically adjusting beam cutback.

It was followed it up by a description of some commonly used helper methods to find certain named elements and family symbols in a project. One of them is FindElement, implemented as follows in that post:

  public static Element FindElement(
    Document doc,
    Type targetType,
    string targetName )
    // Get the elements of the given class 
    FilteredElementCollector collector 
      = new FilteredElementCollector( doc );
      new ElementClassFilter( targetType ) );
    // Parse the collection for the 
    // given name using LINQ query.
    IEnumerable<Element> targetElems =
      from element in collector
      where element.Name.Equals( targetName )
      select element;
    IList<Element> elems = targetElems.ToList();
    if( elems.Count > 0 )
      // We should have only one with the given name.
      return elems[0];
    // Cannot find it.
    return null;

It is important to be aware that this method can be optimised further in some aspects and should not be used indiscriminately.

Here are some points I would like to highlight:

  1. Language dependence: should be avoided if possible.
  2. Speed: could be improved by using a parameter filter instead of LINQ.
  3. Conversion from a filtered element collector to .NET collections can often be avoided.

I avoid using the helper methods in this form wherever I can if performance is a factor. When is it not?

It is not always possible to avoid the language dependence. In any case, it is definitely important to be aware of the issue.

In detail:

  1. Language dependence: if there is any way to identify the target element except by name, it is normally preferable to do so.
  2. Speed: using a parameter filter to find a name may be complicated by the fact that different Revit element types store their names in different parameter values. The LINQ query can mostly be replaced by a parameter filter, though, which normally halves the execution time, since the marshalling of all the non-target data from internal Revit memory to external .NET and LINQ space is eliminated.
  3. A filtered element collector is already iterable, so the conversion to an IEnumerable<Element> and to IList<Element> is often unnecessary. If all filtering can be achieved using filtered element collector functionality, the instantiation of additional lists and consequent duplication and copying of all contained data members can be completely avoided. This is obviously especially important for large collections.

I mentioned performance hints such as these numerous times in the past between the lines. Maybe the time is ripe now to bring them up as a topic of their own.

Mikako underlines that the main intention of the helper method above is to make it as easy as possible for the reader to copy and paste these code snippets to quickly run the test command instead of having to download, explore and install the whole ADN training material zip file, and performance is a completely secondary consideration.

If performance becomes a bottleneck, each developer needs examine it and implement her own optimised version. Accessing a wall type, for example, does not require this kind of filtering from the whole element list.

Collector Optimisation

While we are on the topic of efficient coding, here is another snippet of typical add-in code presenting a surprising number of opportunities for improvement in a very few lines.

It retrieves all family symbols in the document, uses them to find door families, and processes each one in turn:

  FilteredElementCollector collector 
    = new FilteredElementCollector( doc );
  FilteredElementIterator itor = collector
    .OfClass( typeof( FamilySymbol ) )
  while( itor.MoveNext() )
    FamilySymbol symbol = itor.Current
      as Autodesk.Revit.DB.FamilySymbol;
    // Determine family category
    Category cat = symbol.Category;
    // Process family if doors category
    if( cat != null )
      if( cat.Name == "Doors" )
        Family family = symbol.Family;
        // Process reference to doors family

Can you spot three possibilities for improvement, either a more succinct formulation, performance enhancement, or both? And manage not to peek?

Here are the ones I found, which is not to say that there are no others:

Applying these suggestions produces this instead:

  FilteredElementCollector collector
  = new FilteredElementCollector( doc )
    .OfCategory( BuiltInCategory.OST_Doors )
    .OfClass( typeof( FamilySymbol ) );
  foreach( FamilySymbol symbol in collector )
    Family family = symbol.Family;
    // Process reference to doors family

Shorter, more readable, and more performant.

Since each family can contain more than one symbol, you should obviously keep track of the families already processed and skip those when looping over the symbols.