RMarkdown Beamer TOC empty - r-markdown

Question

Using beamer in RMarkdown for presentations, I can't figure out why the TOC is empty. I have tried using a MacBook and Windows.
---
title: "test"
author: "my name"
date: "12/6/2016"
output:
beamer_presentation:
keep_tex: true
toc: true
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```
# Slide 1
Slide content
# Slide 2
Slide content
Outputs the pdf presentation with a title slide, an empty page (where the TOC should be), and then the two slides.
On Windows platform:
> R.version
platform x86_64-w64-mingw32
arch x86_64
os mingw32
system x86_64, mingw32
status
major 3
minor 3.1
year 2016
month 06
day 21
svn rev 70800
language R
version.string R version 3.3.1 (2016-06-21)
nickname Bug in Your Hair
RStudio:0.99.896
Rmarkdown: 1.2
knitr: 1.15.1
Somewhat related question here: Table of content in beamer generated with R markdown/knitr
Using the keep_tex: true argument in the YAML, I see from the tex file that the level 1 headers (i.e. # Section) are not being properly converted to sections in the tex file. For example, from the tex file:
\begin{frame}{Slide 1}
Slide content
\end{frame}
It seems that RMarkdown is not making the tex file correctly.

Answer 1

As pointed out here, the TOC will list the sections (as defined by single #'s), and the slide level must be a level below the sections (defined below in the YAML as slide_level: 2 and in the presentation by ##'s). I don't completely understand why you can't have sections at the slide level, but at least this works.
---
title: "test"
author: "my name"
date: "12/6/2016"
output:
beamer_presentation:
keep_tex: true
toc: true
slide_level:2
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```
# Section 1
## Slide 1
Slide content
# Section 2
# Slide 2
Slide content