listings style within both environments and inline

Question

I am trying to use listings to create some code. The MWE below works and produces the desired output. The problem is that everything is created twice, in that if I want to change the keyword colour to red I need to make two edits instead of just one. So in some sense I want to use \lstset within lstinline or somehow make use of Rstyle within lstnewenvironment. I tried combinations of these by trial and error and only seemed to have errors.

\documentclass{article}

\usepackage{listings}
\usepackage{xcolor}


\lstnewenvironment{R}{\lstset{
  language=R,
  backgroundcolor=\color{yellow!30!white},
  basicstyle={\footnotesize\ttfamily\color{black}},
  keywordstyle=\color{blue},
  stringstyle=\color{green!50!black},
}}{}


\lstdefinestyle{Rstyle}
{
  language=R,
  backgroundcolor=\color{yellow!30!white},
  basicstyle={\footnotesize\ttfamily\color{black}},
  keywordstyle=\color{blue},
  stringstyle=\color{green!50!black},
}

\newcommand{\Rinline}[1]{\lstinline[style=Rstyle]{#1}}


%%%%%%%%%%%%%%%%%%% 
\begin{document}

\begin{R}
x <- length(db[db=="Red"])
\end{R}


\Rinline{x <- length(db[db=="Red"])}


\end{document}

Answer 1

Simple just use style=Rstyle in your env definition.

I use this extensively in my SASnRdisplay package

Answer 2

Hope you are expecting columns=fixed tag, and the tags are follows:

\documentclass{article}

\usepackage{listings}
\usepackage{xcolor}


\lstnewenvironment{R}{\lstset{
  language=R,columns=fixed,
%  backgroundcolor=\color{yellow!30!white},
  basicstyle={\footnotesize\ttfamily\color{black}},
  keywordstyle=\color{blue},
  stringstyle=\color{green!50!black},
}}{}


\lstdefinestyle{Rstyle}
{
  language=R,columns=fixed,
%  backgroundcolor=\color{yellow!30!white},
  basicstyle={\footnotesize\ttfamily\color{black}},
  keywordstyle=\color{blue},
  stringstyle=\color{green!50!black},
}

\newcommand{\Rinline}[1]{\lstinline[style=Rstyle]{#1}}


%%%%%%%%%%%%%%%%%%% 
\begin{document}

\begin{R}
x <- length(db[db=="Red"])
\end{R}

\noindent
\Rinline{x <- length(db[db=="Red"])}


\end{document}

Output:

Note that I've removed the option backgroundcolor=\color{yellow!30!white} from your MWE...