Calling .NET/C# from R

Exposing the .NET dll as COM dll and then calling a COM object in the dll from R seem to be the only way. And there is a package for it: http://cran.r-project.org/web/packages/rcom/rcom.pdf

If you cannot make a COM dll because it's third-party dll, you can always create a new interface-like .NET dll with COM interface where you can call actual dll.

Another option that readers of this discussion might consider is the rClr package, which I have been working on for a couple of years to access arbitrary .NET code from R. It is a sibling of R.NET which, conversely, is a way to access R from .NET.

To give a flavour of the rClr package, the canonical "Hello World" looks like:

library(rClr)
clrLoadAssembly('c:/path/to/myassembly.dll')
myObj <- clrNew('MyNamespace.MyClass,MyAssemblyName')
clrCall(myObj, 'SayHelloWorld')

Feedback and suggestions welcome via the web site.