If there is, it would be in the iTunes Store. I've found a few statistics packages, but no release of R or anything close to its power. Perhaps someone else will have a recommendation. Or you can search the iTunes Store for "statistics" or something similar and see if anything turns up that would work for you.
I'd allready searched for it in the iTunes Store (the portuguese one) but all I could find was some apps, none of them with the power of R.
I read in a post (don't remember where) that it would be difficult to implement R in iOS due to the fact R is a programming language and the restrictions that Apple impose on their iOS apps. I don't understand why, because Codea is an iOS app. But I'm not a versed person in this matters...
I believe that the iPad is already able to handle most of the R packages.
At one time Apple did not allow other interpreters in iOS, but they relaxed that stricture a year or more ago now, though something like R might still be prohibited. Even if allowed, it's a pretty complex problem, since R uses FORTRAN which isn't supported in iOS. Even if R got ported, packages that use FORTRAN, tcl/tk, Java, Perl or other such libraries wouldn't work which probably would seriously limit the use of R in many cases.
For now, at least, probably your only option is to take control of a computer with R from your iPad.