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(This article was first published on <strong><a href="http://itsalocke.com/r-quick-tip-sequential-yaml-headers-rmarkdown-parameter-re-use/"> R – Locke Data</a></strong>, and kindly contributed to <a rel="nofollow" href="https://www.r-bloggers.com/">R-bloggers)</a> </div>
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<p>Ever wondered how to make an rmarkdown title dynamic? Maybe, wanted to use a parameter in multiple locations? Maybe wanted to pass through a publication date? Advanced use of YAML headers can help!</p>
<p>Normally, when we write rmarkdown, we might use something like the basic YAML header that the rmarkdown template gives us.</p>
<pre><code>---
title: &quot;My report&quot;
date: &quot;18th April, 2017&quot;
output: pdf_document
---
</code></pre>
<p>You may already know the trick about making the date dynamic to whatever date the report gets rendered on by using the inline R execution mode of rmarkdown to insert a value.</p>
<pre><code>---
title: &quot;My report&quot;
date: &quot;`r Sys.Date()`&quot;
output: pdf_document
---
</code></pre>
<p>What you may not already know is that YAML fields get evaluated sequentially so you can use a value created further up in the <code>params</code> section, to use it later in the block.</p>
<pre><code>---
params:
  dynamictitle: &quot;My report&quot;
  reportdate: !r Sys.Date()
output: pdf_document
title: &quot;`r params$dynamictitle`&quot;
date: &quot;`r params$reportdate`&quot;
---
</code></pre>
<p>By doing this, you can then pass parameter values into the <code>render()</code> function when you want to generate a report.</p>
<pre><code>rmarkdown::render(&quot;MWE.Rmd&quot;, 
    params=list(dynamictitle=&quot;New&quot;,
                reportdate=Sys.Date()-1)
                )
</code></pre>
<p>Parameter re-use within rmarkdown enables you to dynamically generate vital metadata for the report and use values in multiple places within the document. Very handy!</p>
<p>The post <a target="_blank" rel="nofollow" href="http://itsalocke.com/r-quick-tip-sequential-yaml-headers-rmarkdown-parameter-re-use/">R Quick Tip: parameter re-use within rmarkdown YAML</a> appeared first on <a target="_blank" rel="nofollow" href="http://itsalocke.com/">Locke Data</a>. Locke Data are a data science consultancy aimed at helping organisations get ready and get started with data science.</p>
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