Hi I need some advice. Note: I do not know anything from C apart from my 2 days of research. I am currently trying to make meaning of the modelmatrix function (written in C) and called from R function model.matrix() via .External2. In trying to view the source code (in R) for model.matrix(), I have been reasonably succesful thanks to the debug command. This command was good because I was able to check line-by-line what the code was doing and obtain an output within my R console. Furthermore, checking the values of each of my variables while sequentially moving through the lines was also very useful. However, just by looking at the R source code, it is insufficient in understanding most of the computation. I have to look within the C code. In particular, within model.matrix(), a .External2 call is executed to a C function named modelmatrix. I downloaded the source from the website and can view the function modelmatrix(in model.c) in a text editor. I am now finding a way to play with the code so I understand whats going on and I don't know what's the best way to do this. I* was wondering whether there is an equivalent way as the debug function to check C code line by line. ie each line of code are typed in, and an output is obtained*. I know a package "inline" allows you to build C functions and use them in R. But I can't find anything which does what I want. * If this is not possible, is there an alternative good, easy way to run through and understand the commands in C that anyone knows about.* -- Yours sincerely, Justin *I check my email at 9AM and 4PM everyday* *If you have an EMERGENCY, contact me at +447938674419(UK) or +60125056192(Malaysia)* [[alternative HTML version deleted]]