Add beamer frame options in knitr/rmarkdown - r

Question

I'm trying to add frame numbers to my Beamer presentation written in rmarkdown. However, I would like to suppress the numbers on the title page using the \begin{frame}[plain] option (from the second answer here: https://tex.stackexchange.com/questions/82794/removing-page-number-from-title-frame-without-changing-the-theme). However, when compiling from rmarkdown to tex, the \titlepage already creates a frame environment, so in effect I get a double frame and thus an error.
So when compiling this:
---
output:
beamer_presentation:
includes:
in_header: header.tex
---
\begin{frame}[plain]
\titlepage
\end{frame}
I get this in latex:
\begin{frame{
\begin{frame}
\titlepage
\end{frame}
\end{frame}
In the header.tex I have this:
\let\otp\titlepage
\renewcommand{\titlepage}{\otp\addtocounter{framenumber}{-1}}
So my workaround now is to just use a plain \maketitle in rmarkdown, then compile to .tex, add the [plain] option, then compile to pdf. However, I would like to avoid that intermediate step. Is this possible in rmarkdown?

Answer 1

rmarkdown uses pandoc to convert a Rmd file to a pdf via beamer/latex. pandoc uses templates to control how the conversion goes.
One way to deal with your problem is to :
Download the default beamer template rmarkdown uses and open it.
Change line 137 from this :
\frame{\titlepage}
To this :
\frame[plain]{\titlepage}
Add the path to your modified template in your Rmd file :
---
output:
beamer_presentation:
includes:
in_header: header.tex
template:/path/to/new/template.tex
---
Note that you need to specify the whole path, or store the template where pandoc can find it (~/.pandoc/templates on a linux machine)

Answer 2

Add {.plain} after the title as in:
----
# I'm the title {.plain}
Source: Pandoc User’s Guide