Harvard citation format in R markdown - r

Question

I am using R markdown for a document, however I just have to do some minor tweaks to my citations.
Firstly, is there a package which will put my BibTeX references in Harvard format?
And secondly, how can I get the author's surname and the year to be seperated by a comma within my in-text citations?
Here is one of the references in my BibTex file
#article{schwarz1978estimating,
title={Estimating the dimension of a model},
author={Schwarz, Gideon and others},
journal={The annals of statistics},
volume={6},
number={2},
pages={461--464},
year={1978},
publisher={Institute of Mathematical Statistics}
}
When I in-text reference this, it generates (Schwarz 1978). I would like a comma to seperate the surname and the year.
I've also added my YAML if that is needed
### Adding additional latex packages:
header-includes:
- \usepackage{rotating, caption} \DeclareMathOperator*{\argmin}{argmin}
- \usepackage{booktabs}
- \usepackage{longtable}
- \usepackage{array}
- \usepackage{multirow}
- \usepackage{wrapfig}
- \usepackage{float}
- \usepackage{colortbl}
- \usepackage{pdflscape}
- \usepackage{tabu}
- \usepackage{threeparttable}
- \usepackage{threeparttablex}
- \usepackage[normalem]{ulem}
- \usepackage{makecell}
- \usepackage{xcolor}
output:
pdf_document:
keep_tex: yes
template: Tex/TexDefault.txt
fig_width: 3.5 # Adjust default figure sizes. This can also be done in the chunks of the text.
fig_height: 3.5

Answer 1

I rely on the standard (and very powerful) natbib package which many Rmd styles already add, and which you can generally add to whichever RMarkdown template you use (and you didn't say).
Quick example using my pinp package:
---
title: Example
author:
- name: Dirk Eddelbuettel
affiliation: a
address:
- code: a
address: Planet Earth
papersize: letter
fontsize: 12pt
one_column: true
bibliography: ref
output: pinp::pinp
---
# Introduction
Two quick examples using natbib
- citet: \citet{schwarz1978estimating}
- citep: \citep{schwarz1978estimating}
For the rest, see the natbib documentation, either at source or contributed
such as https://gking.harvard.edu/files/natnotes2.pdf.
The body of that document comes out as follows: