How can I get R and Tikz to cooperate in a loop?

Question

I'm using knitr and compiling my .Rnw file in Rstudio. Here's a MWE illustrating my issue. I want the code below to output "1, 2, 3" but instead it gives me "1, 1, 1".

%%%%%%%%%%%%%%%%
\documentclass[border=20pt]{standalone}
\usepackage{tikz}
\begin{document}

<<eval=TRUE, echo=FALSE, results='hide'>>=
faux.data<-c(1,2,3)
i<-1    # set loop index to 1
@

\begin{tikzpicture}
\foreach \x in {1,2,3}
   {\node[draw, circle] at (\x,0) {\Sexpr{faux.data[i]}};

   <<eval=TRUE, echo=FALSE, results='hide'>>=
   i<-i+1  #advance loop index
   @
   }

\end{tikzpicture}
\end{document}
%%%%%%%%%%%%%%%%%