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Expand Down Expand Up @@ -335,14 +399,233 @@ <h1 class="title">2023-NHSR-Conf-Presentation</h1>
</div>

</section>
<section id="quarto" class="slide level2">
<h2>Quarto</h2>
<p>Quarto enables you to weave together content and executable code into a finished document. To learn more about Quarto see <a href="https://quarto.org" class="uri">https://quarto.org</a>.</p>
<section class="slide level2">

<style>
.highlighted {
background-color: yellow;
}
</style>
</section>
<section id="purrr" class="slide level2">
<h2>purrr</h2>

<img data-src="purrr_logo.png" class="r-stretch quarto-figure-center"><p>Ahhh, cute cat…</p>
</section>
<section id="scary-functional-programming" class="slide level2">
<h2>Scary functional programming</h2>

<img data-src="purrr_logo.png" class="r-stretch quarto-figure-center"><p>Run away now!</p>
</section>
<section id="aims" class="slide level2">
<h2>Aims</h2>
<ul>
<li class="fragment">Not scary!</li>
</ul>
<div class="fragment">
<div>
<ul>
<li>Practical intro to purrr</li>
<li>Focus on a “mental model” which helped me</li>
<li>Simple examples</li>
</ul>
</div>
</div>
<div class="fragment">
<p>Functional programming is something we can save for another day (and another speaker!)</p>
</div>
</section>
<section id="the-package-website" class="slide level2">
<h2>The package website</h2>
<p>From the tidyverse documentation:</p>
<blockquote>
<p>“the best place to start is the family of map() functions which allow you to replace many for loops with code that is both more succinct and easier to read.”</p>
</blockquote>
<p>and:</p>
<blockquote>
<p>“The best place to learn about the map() functions is the <a href="https://r4ds.had.co.nz/iteration.html">iteration chapter in R for data science.</a>”</p>
</blockquote>
<aside class="notes">
<p>Purrr is part of the tidyverse, and both of these comments are true.</p>
<p>The first hints at the fact that once you grasp the map() function, you’ll already be able to use it’s close relations in helpful ways.</p>
<p>The second says the best place to learn is Hadley’s book R for Data Science. In the meantime I hope this presentation helps!</p>
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</section>
<section id="looping" class="slide level2">
<h2>Looping</h2>
<div class="cell">
<div class="sourceCode cell-code" id="cb1"><pre class="sourceCode numberSource r number-lines code-with-copy"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1"></a><span class="co"># we need a vector to iterate over</span></span>
<span id="cb1-2"><a href="#cb1-2"></a>food <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">"croissant"</span>, <span class="st">"baked potato"</span>)</span>
<span id="cb1-3"><a href="#cb1-3"></a></span>
<span id="cb1-4"><a href="#cb1-4"></a><span class="co"># we need to create a place to put the results (the right size)</span></span>
<span id="cb1-5"><a href="#cb1-5"></a>result <span class="ot">&lt;-</span> <span class="fu">vector</span>(<span class="st">"character"</span>, <span class="fu">length</span>(food))</span>
<span id="cb1-6"><a href="#cb1-6"></a></span>
<span id="cb1-7"><a href="#cb1-7"></a><span class="co"># here's the loop</span></span>
<span id="cb1-8"><a href="#cb1-8"></a><span class="cf">for</span>(i <span class="cf">in</span> <span class="fu">seq_along</span>(food)){</span>
<span id="cb1-9"><a href="#cb1-9"></a> </span>
<span id="cb1-10"><a href="#cb1-10"></a> result[[i]] <span class="ot">&lt;-</span> <span class="fu">paste</span>(<span class="st">"Hot"</span>, food[[i]])</span>
<span id="cb1-11"><a href="#cb1-11"></a> </span>
<span id="cb1-12"><a href="#cb1-12"></a>}</span>
<span id="cb1-13"><a href="#cb1-13"></a></span>
<span id="cb1-14"><a href="#cb1-14"></a>result</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
<div class="cell fragment">
<div class="cell-output cell-output-stdout">
<pre><code>[1] "Hot croissant" "Hot baked potato"</code></pre>
</div>
</div>
</section>
<section id="mapping" class="slide level2">
<h2>Mapping</h2>
<div class="cell">
<div class="sourceCode cell-code" id="cb3"><pre class="sourceCode numberSource r number-lines code-with-copy"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1"></a><span class="co"># we still need a vector to iterate over</span></span>
<span id="cb3-2"><a href="#cb3-2"></a>food <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">"croissant"</span>, <span class="st">"baked potato"</span>)</span>
<span id="cb3-3"><a href="#cb3-3"></a></span>
<span id="cb3-4"><a href="#cb3-4"></a><span class="co"># we create a function to do the "work"</span></span>
<span id="cb3-5"><a href="#cb3-5"></a>heat_the_food <span class="ot">&lt;-</span> <span class="cf">function</span>(food){</span>
<span id="cb3-6"><a href="#cb3-6"></a> </span>
<span id="cb3-7"><a href="#cb3-7"></a> <span class="fu">paste</span>(<span class="st">"Hot"</span>, food)</span>
<span id="cb3-8"><a href="#cb3-8"></a></span>
<span id="cb3-9"><a href="#cb3-9"></a>}</span>
<span id="cb3-10"><a href="#cb3-10"></a></span>
<span id="cb3-11"><a href="#cb3-11"></a><span class="co"># here's the loop</span></span>
<span id="cb3-12"><a href="#cb3-12"></a>result <span class="ot">&lt;-</span> purrr<span class="sc">::</span><span class="fu">map</span>(food, heat_the_food)</span>
<span id="cb3-13"><a href="#cb3-13"></a></span>
<span id="cb3-14"><a href="#cb3-14"></a>result</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
<div class="cell fragment">
<div class="cell-output cell-output-stdout">
<pre><code>[1] 2</code></pre>
<pre><code>[[1]]
[1] "Hot croissant"

[[2]]
[1] "Hot baked potato"</code></pre>
</div>
</div>
<aside class="notes">
<p>Ignore for a moment the shape of the result. In the loop example we got a vector back. In the map example we have a list. We’ll come back to that shortly.</p>
<p>But even with that difference you’re sceptical. Tom, you’re short-changing us. We’re happy with loops. 14 lines of code. You’re talking about map() being simpler, and you still took 14 lines.</p>
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</section>
<section id="comparison" class="slide level2" data-auto-animate="true">
<h2 data-id="quarto-animate-title">Comparison</h2>
<p>loop</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode numberSource r number-lines code-with-copy" data-id="quarto-animate-code"><code class="sourceCode r hljs"><span id="cb5-1" class="hljs-ln-code"><a href="#cb5-1"></a></span>
<span id="cb5-2" class="hljs-ln-code"><a href="#cb5-2"></a><span class="co"># we need a vector to iterate over</span></span>
<span id="cb5-3" class="hljs-ln-code"><a href="#cb5-3"></a>food <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">"croissant"</span>, <span class="st">"baked potato"</span>)</span>
<span id="cb5-4" class="hljs-ln-code"><a href="#cb5-4"></a></span>
<span id="cb5-5" class="hljs-ln-code"><a href="#cb5-5"></a><span class="co"># we need to create a place to put the results (the right size)</span></span>
<span id="cb5-6" class="hljs-ln-code"><a href="#cb5-6"></a>result <span class="ot">&lt;-</span> <span class="fu">vector</span>(<span class="st">"character"</span>, <span class="fu">length</span>(food))</span>
<span id="cb5-7" class="hljs-ln-code"><a href="#cb5-7"></a></span>
<span id="cb5-8" class="hljs-ln-code"><a href="#cb5-8"></a><span class="co"># here's the loop</span></span>
<span id="cb5-9" class="hljs-ln-code"><a href="#cb5-9"></a><span class="cf">for</span>(i <span class="cf">in</span> <span class="fu">seq_along</span>(food)){</span>
<span id="cb5-10" class="hljs-ln-code"><a href="#cb5-10"></a> </span>
<span id="cb5-11" class="hljs-ln-code"><a href="#cb5-11"></a> result[[i]] <span class="ot">&lt;-</span> <span class="fu">paste</span>(<span class="st">"Hot"</span>, food[[i]])</span>
<span id="cb5-12" class="hljs-ln-code"><a href="#cb5-12"></a> </span>
<span id="cb5-13" class="hljs-ln-code"><a href="#cb5-13"></a>}</span>
<span id="cb5-14" class="hljs-ln-code"><a href="#cb5-14"></a></span>
<span id="cb5-15" class="hljs-ln-code"><a href="#cb5-15"></a>result</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="comparison-1" class="slide level2" data-auto-animate="true">
<h2 data-id="quarto-animate-title">Comparison</h2>
<p>map</p>
<div class="sourceCode" id="cb6"><pre class="sourceCode numberSource r number-lines code-with-copy" data-id="quarto-animate-code"><code class="sourceCode r hljs"><span id="cb6-1" class="hljs-ln-code"><a href="#cb6-1"></a></span>
<span id="cb6-2" class="hljs-ln-code"><a href="#cb6-2"></a><span class="co"># we need a vector to iterate over</span></span>
<span id="cb6-3" class="hljs-ln-code"><a href="#cb6-3"></a>food <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">"croissant"</span>, <span class="st">"baked potato"</span>)</span>
<span id="cb6-4" class="hljs-ln-code"><a href="#cb6-4"></a></span>
<span id="cb6-5" class="hljs-ln-code"><a href="#cb6-5"></a><span class="co"># we create a function to do the "work"</span></span>
<span id="cb6-6" class="hljs-ln-code"><a href="#cb6-6"></a>heat_the_food <span class="ot">&lt;-</span> <span class="cf">function</span>(food){</span>
<span id="cb6-7" class="hljs-ln-code"><a href="#cb6-7"></a> </span>
<span id="cb6-8" class="hljs-ln-code"><a href="#cb6-8"></a> <span class="fu">paste</span>(<span class="st">"Hot"</span>, food)</span>
<span id="cb6-9" class="hljs-ln-code"><a href="#cb6-9"></a></span>
<span id="cb6-10" class="hljs-ln-code"><a href="#cb6-10"></a>}</span>
<span id="cb6-11" class="hljs-ln-code"><a href="#cb6-11"></a></span>
<span id="cb6-12" class="hljs-ln-code"><a href="#cb6-12"></a><span class="co"># here's the loop</span></span>
<span id="cb6-13" class="hljs-ln-code"><a href="#cb6-13"></a>result <span class="ot">&lt;-</span> purrr<span class="sc">::</span><span class="fu">map</span>(food, heat_the_food)</span>
<span id="cb6-14" class="hljs-ln-code"><a href="#cb6-14"></a></span>
<span id="cb6-15" class="hljs-ln-code"><a href="#cb6-15"></a>result</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="comparison-2" class="slide level2" data-auto-animate="true">
<h2 data-id="quarto-animate-title">Comparison</h2>
<p>loop</p>
<div class="sourceCode" id="cb7" data-code-line-numbers="|6|9|11"><pre class="sourceCode numberSource r number-lines code-with-copy" data-id="quarto-animate-code"><code class="sourceCode r hljs"><span id="cb7-1" class="hljs-ln-code"><a href="#cb7-1"></a></span>
<span id="cb7-2" class="hljs-ln-code"><a href="#cb7-2"></a><span class="co"># we need a vector to iterate over</span></span>
<span id="cb7-3" class="hljs-ln-code"><a href="#cb7-3"></a>food <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">"croissant"</span>, <span class="st">"baked potato"</span>)</span>
<span id="cb7-4" class="hljs-ln-code"><a href="#cb7-4"></a></span>
<span id="cb7-5" class="hljs-ln-code"><a href="#cb7-5"></a><span class="co"># we need to create a place to put the results (the right size)</span></span>
<span id="cb7-6" class="hljs-ln-code"><a href="#cb7-6"></a>result <span class="ot">&lt;-</span> <span class="fu">vector</span>(<span class="st">"character"</span>, <span class="fu">length</span>(food))</span>
<span id="cb7-7" class="hljs-ln-code"><a href="#cb7-7"></a></span>
<span id="cb7-8" class="hljs-ln-code"><a href="#cb7-8"></a><span class="co"># here's the loop</span></span>
<span id="cb7-9" class="hljs-ln-code"><a href="#cb7-9"></a><span class="cf">for</span>(i <span class="cf">in</span> <span class="fu">seq_along</span>(food)){</span>
<span id="cb7-10" class="hljs-ln-code"><a href="#cb7-10"></a> </span>
<span id="cb7-11" class="hljs-ln-code"><a href="#cb7-11"></a> result[[i]] <span class="ot">&lt;-</span> <span class="fu">paste</span>(<span class="st">"Hot"</span>, food[[i]])</span>
<span id="cb7-12" class="hljs-ln-code"><a href="#cb7-12"></a> </span>
<span id="cb7-13" class="hljs-ln-code"><a href="#cb7-13"></a>}</span>
<span id="cb7-14" class="hljs-ln-code"><a href="#cb7-14"></a></span>
<span id="cb7-15" class="hljs-ln-code"><a href="#cb7-15"></a>result</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p>There is more “boilerplate” code in a loop, and code explanations end up in comments (or don’t exist)</p>
</section>
<section id="comparison-3" class="slide level2" data-auto-animate="true">
<h2 data-id="quarto-animate-title">Comparison</h2>
<p>map</p>
<div class="sourceCode" id="cb8" data-code-line-numbers="|6|8|13"><pre class="sourceCode numberSource r number-lines code-with-copy" data-id="quarto-animate-code"><code class="sourceCode r hljs"><span id="cb8-1" class="hljs-ln-code"><a href="#cb8-1"></a></span>
<span id="cb8-2" class="hljs-ln-code"><a href="#cb8-2"></a><span class="co"># we need a vector to iterate over</span></span>
<span id="cb8-3" class="hljs-ln-code"><a href="#cb8-3"></a>food <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">"croissant"</span>, <span class="st">"baked potato"</span>)</span>
<span id="cb8-4" class="hljs-ln-code"><a href="#cb8-4"></a></span>
<span id="cb8-5" class="hljs-ln-code"><a href="#cb8-5"></a><span class="co"># we create a function to do the "work"</span></span>
<span id="cb8-6" class="hljs-ln-code"><a href="#cb8-6"></a>heat_the_food <span class="ot">&lt;-</span> <span class="cf">function</span>(food){</span>
<span id="cb8-7" class="hljs-ln-code"><a href="#cb8-7"></a> </span>
<span id="cb8-8" class="hljs-ln-code"><a href="#cb8-8"></a> <span class="fu">paste</span>(<span class="st">"Hot"</span>, food)</span>
<span id="cb8-9" class="hljs-ln-code"><a href="#cb8-9"></a></span>
<span id="cb8-10" class="hljs-ln-code"><a href="#cb8-10"></a>}</span>
<span id="cb8-11" class="hljs-ln-code"><a href="#cb8-11"></a></span>
<span id="cb8-12" class="hljs-ln-code"><a href="#cb8-12"></a><span class="co"># here's the loop</span></span>
<span id="cb8-13" class="hljs-ln-code"><a href="#cb8-13"></a>result <span class="ot">&lt;-</span> purrr<span class="sc">::</span><span class="fu">map</span>(food, heat_the_food)</span>
<span id="cb8-14" class="hljs-ln-code"><a href="#cb8-14"></a></span>
<span id="cb8-15" class="hljs-ln-code"><a href="#cb8-15"></a>result</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p>The code is easier to read, and we can use function names not comments to decribe what it’s doing</p>
</section>
<section id="in-detail" class="slide level2">
<h2>In detail</h2>
<p><code>purrr::map(food, heat_the_food)</code></p>
<p><code>purrr::map(.x, .f)</code></p>
<p>.x A list or atomic vector</p>
<p>.f A function</p>
<p><code>purrr::map(your_raw_material, function_containing_your_instructions)</code></p>
</section>
<section id="further-reading-training" class="slide level2">
<h2>Further reading / training</h2>
<p>Tom Jemmett’s excellent video on purrr:<br>
<a href="https://youtu.be/GxvccD8K49M" class="uri">https://youtu.be/GxvccD8K49M</a></p>
<p>The iteration chapter of R for Data Science:<br>
<a href="https://r4ds.had.co.nz/iteration.html#iteration" class="uri">https://r4ds.had.co.nz/iteration.html#iteration</a></p>
<p>The purrr docs:<br>
<a href="https://purrr.tidyverse.org" class="uri">https://purrr.tidyverse.org</a></p>
</section>
<section id="open-source" class="slide level2">
<h2>Open source</h2>
<p>This presentation:<br>
<a href="https://github.com/ThomUK/2023-NHSR-Conf-Presentation" class="uri">https://github.com/ThomUK/2023-NHSR-Conf-Presentation</a></p>
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