Plot two figures side by side in knitr without changing mfrow?

Question

I would like to plot 2 figures side-by-side using knitr. I know I could use par(mfrow=c(1,2)), but I've done a lot of work making the figures just right as they are. I've seen this (Two column layout with text and knitr chunk), and it's not working for me.

Ideally, I'd like to do something like this (which fails):

\documentclass[a4paper,11pt]{article}
\begin{document}
\begin{frame}
   \begin{columns}
      \begin{column}{.5\linewidth}
          <<echo=FALSE,eval=TRUE,out.width='4cm',out.height='4cm'>>=
             plot(1:10)
          @
      \end{column}
      \begin{column}{.5\linewidth}
          <<echo=FALSE,eval=TRUE,out.width='4cm',out.height='4cm'>>=
             plot(1:10)
          @
      \end{column}
    \end{columns}
\end{frame}
\end{document}

Using Sweave, I could do the following:

<<plot1, echo=FALSE,eval=TRUE>>=
    plot(1:10)
@

\begin{figure}[htbp]
  \begin{minipage}[h]{0.5\linewidth}
    \begin{center}

        <<label=figplotFlowSingle,echo=FALSE>>=
            <<plot1>>
        @
    \subcaption{Default plot1}
    \label{fig:plot1}
    \end{center}
  \end{minipage}
  \begin{minipage}[h]{0.5\linewidth}
    \begin{center}

        <<plot2, echo=FALSE,eval=TRUE>>=
             plot(1:10)
        @

        <<label=plot22,echo=FALSE>>=
            <<plot2>>
         @
    \subcaption{Default plot2}
    \label{fig:plot2}
    \end{center}
  \end{minipage}
  \caption{}
  \label{fig:plot1and2}
\end{figure}

Answer 1

If all you want is two figures side by side, you can put the code in one chunk and set fig.show='hold' with an appropriate width, e.g.

\documentclass{article}

\begin{document}  

<<test, out.width='4cm', out.height='4cm', fig.show='hold'>>=
plot(1:10)
plot(rnorm(100))
@

\end{document}

If you want to center the figures, just add an option fig.align='center'. If you want to add captions, you can use fig.cap. See the documentation for all possible options here.