[R] Sample Size Calculation using a Drop the Loser/Keep the Winner Design

[Paul Miller]

Hello Everyone,
 
I need to perform a sample size calculation using a drop the loser/keep the winner design. I've been searching for examples of how to do this using R but haven't found much. 
 
The most promising possibility thus far is an R function called DrpLsrNRst. This appears in the book "Adaptive Design Theory and Implementation Using SAS and R". I found the function online but there's a copyright statement saying it can only be used by those who have purchased the book.
 
I thought about purchasing the book, but a reviewer on Amazon indicated it's mostly a SAS book with a little R code thrown in and an examination of the TOC suggests this is the case. I'm still primarily a SAS user, but am in the process of changing that. So I'm shying away from purchasing what I perceive to be a SAS book unless it's really necessary.
 
Does anyone know of any other resources? 
 
Thanks,
 
Paul