C＃嵌套的foreach循环优化

Question

I've got a nested foreach loop that I really need to cut the computation time on. Each collection is at about 50 members, so the extrapolation is huge. I've looked at a lot of information about SelectMany, but I'm still not entirely sure how to use it, or if it's the correct solution.

List<string> StringList; //Populated in previous code
Type[] assemblyTypes = RandomAssembly.GetTypes();

foreach (String name in StringList)
{                               
  foreach (Type at in assemblyTypes)
  {                             
    if (name == at.Name)
    {                                       
      //Do stuff.
    }
  }
}

Thanks in advance!

Answer 1

Use a lookup (such as a dictionary) to increase the speed of checking for a type name:

List<string> StringList; //Populated in previous code
Dictionary<string,Type> assemblyTypes = RandomAssembly.GetTypes()
    .ToDictionary(t => t.Name, t => t);

foreach (String name in StringList)
{                               
    if (assemblyTypes.ContainsKey(name))
    {                                       
      //Do stuff.
    }
  }
}

You should also check which of the 2 collections ( StringList or assemblyTypes ) is likely to be larger. You generally want the larger one to be converted to the lookup in order to reduce the number of iterations.

Answer 2

Load Type[] into a Dictionary or HashSet (depending on your version of .NET) and then the inner loop disappears.

List<string> StringList; //Populated in previous code
Type[] assemblyTypes = RandomAssembly.GetTypes();
Dictionary<String,Type> typesHash = new Dictionary<String,Type>();
foreach ( Type type in assemblyTypes ) {
  typesHash.Add( type.Name, type );
}

foreach (String name in StringList) {                               
  Type type = null;
  if ( typesHash.TryGetValue( name, out type ) ) {
    // do something with type
  }
}

Answer 3

You might try something like:

assemblyTypes.Where(x => StringList.Contains(x.Name));

Keep in mind this is case sensitive and ignores whitespace, so you will need to add case consideration or trimming if that's an issue.

Edit: (example for loop usage)

foreach (Type item in assemblyTypes.Where(x => StringList.Contains(x.Name)))
{
    // Do stuff
}

Answer 4

如果您的数组/列表包含许多项，则可以尝试使用Parallel ForEach循环 。

Answer 5

The best optimization might be by querying not for the name but instead for an implemented interface.

Make sure you are optimizing the correct issue/part of your code.