避免每次在Rmarkdown中编译整个文档

I am a new user to R Markdown and was wondering if there was a way to "incrementally" compile an html markdown page as I am writing the code. Say I add 20 lines of code to an existing markdown file today. Is there a way to have the program "remember" the past compilations so that only the 20 new lines are added to the html file preserving the past rendering. I have a lot of memory heavy steps in my code (loading unloading files), and I find that when I add new bits of code I am having to compile everything from the beginning.I am a new user to R Markdown and was wondering