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<div id="lesson-6-lists-lists-lists-and-applying-functions-with-purrr" class="section level1">
<h1>Lesson 6: Lists, lists, lists and applying functions with <code>purrr</code></h1>
<p> </p>
<p>Functions for Lesson 6<br />
<code>map</code>, <code>pluck</code>, <code>keep</code>, <code>discard</code>, <code>compact</code><br />
</p>
<p>Packages for Lesson 6<br />
<code>dplyr</code>, <code>purrr</code><br />
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<h1>Agenda</h1>
<p>Use the <code>purrr</code> package to apply functions to lists and vectors.</p>
<p><a href="https://purrr.tidyverse.org/">Cheat sheet for the <code>purrr</code> package</a>.<br />
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<div id="do-first" class="section level1">
<h1>Do First</h1>
<p>Recreate the below plot using the smaller NYC Airbnb dataset. The curve is a 'loess'. To change the legend title, add the (unintuitive) <code>colour = "your legend title"</code> argument to the <code>labs()</code> function.</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="co"># smaller csv file (16 cols)</span>
url <-<span class="st"> "http://data.insideairbnb.com/united-states/ny/new-york-city/2021-04-07/data/listings.csv.gz"</span>
nyc <-<span class="st"> </span>readr<span class="op">::</span><span class="kw">read_csv</span>(url)
nyc <-<span class="st"> </span>nyc[nyc<span class="op">$</span>id <span class="op"><</span><span class="st"> </span><span class="fl">1e+06</span>, ] <span class="co"># get smaller subet of data</span></code></pre></div>
<p><img src="Lesson6_files/figure-html/unnamed-chunk-2-1.png" width="100%" /></p>
</div>
<div id="create-some-data-in-a-list" class="section level1">
<h1>Create some data in a list</h1>
<p>First generate some random data</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">s1 <-<span class="st"> </span><span class="kw">sample</span>(<span class="dv">10</span>) <span class="co"># random number sample</span>
s2 <-<span class="st"> </span><span class="kw">rnorm</span>(<span class="dv">10</span>, <span class="dv">500</span>) <span class="co"># sample 10 normally distributed random numbers around a mean of 500 </span>
s3 <-<span class="st"> </span><span class="kw">runif</span>(<span class="dv">10</span>) <span class="co"># random uniform distribution</span>
s1</code></pre></div>
<pre><code> [1] 2 4 1 8 10 5 3 6 7 9</code></pre>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">s2</code></pre></div>
<pre><code> [1] 501.6309 498.4540 499.8142 501.0258 499.9049 499.9875 499.9702 502.5944 501.3363 498.4851</code></pre>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">s3</code></pre></div>
<pre><code> [1] 0.8834566 0.1607566 0.8669604 0.1298742 0.4734379 0.9133809 0.2103161 0.3419445 0.2215991
[10] 0.3468892</code></pre>
<p>Now combine these into a list using <code>list()</code></p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">ls1 <-<span class="st"> </span><span class="kw">list</span>(s1, s2, s3) <span class="co"># create a list of these data</span>
ls1</code></pre></div>
<pre><code>[[1]]
[1] 2 4 1 8 10 5 3 6 7 9
[[2]]
[1] 501.6309 498.4540 499.8142 501.0258 499.9049 499.9875 499.9702 502.5944 501.3363 498.4851
[[3]]
[1] 0.8834566 0.1607566 0.8669604 0.1298742 0.4734379 0.9133809 0.2103161 0.3419445 0.2215991
[10] 0.3468892</code></pre>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">ls1 <span class="op">%>%</span><span class="st"> </span>str</code></pre></div>
<pre><code>List of 3
$ : int [1:10] 2 4 1 8 10 5 3 6 7 9
$ : num [1:10] 502 498 500 501 500 ...
$ : num [1:10] 0.883 0.161 0.867 0.13 0.473 ...</code></pre>
</div>
<div id="exercise-0" class="section level1">
<h1>Exercise 0</h1>
<div id="list-indexing" class="section level2">
<h2>List indexing</h2>
<p>Print the <code>ls1</code> list object and take note of the index and elements</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">ls1
<span class="co"># index</span>
ls1[<span class="dv">1</span>]
ls1[<span class="dv">2</span>]
ls1[<span class="dv">3</span>]
<span class="co"># elements</span>
ls1[[<span class="dv">1</span>]][[<span class="dv">1</span>]]
ls1[[<span class="dv">1</span>]][[<span class="dv">3</span>]]
ls1[[<span class="dv">2</span>]][[<span class="dv">10</span>]]
ls1[[<span class="dv">3</span>]][[<span class="dv">11</span>]] <span class="co"># ??</span>
ls1[[<span class="dv">3</span>]] <span class="op">%>%</span><span class="st"> </span>length
<span class="co"># what's the difference?</span>
ls1[<span class="dv">1</span>]
ls1[[<span class="dv">1</span>]]</code></pre></div>
</div>
<div id="apply-functions" class="section level2">
<h2>Apply functions</h2>
<p>The <code>purrr</code> package uses the following apply functions to apply function iteratively to a list or vector.</p>
<p><code>map</code> Apply a function to each element of a list</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="kw">require</span>(purrr)
<span class="kw">set.seed</span>(<span class="dv">12</span>) <span class="co"># set a number seed to generate reprodicible results for random data </span>
<span class="kw">map</span>(ls1, mean) <span class="co"># get the mean </span></code></pre></div>
</div>
<div id="exercise-1" class="section level2">
<h2>Exercise 1</h2>
<p>Apply summary stats to the <code>ls1</code> list data<br />
* <code>sum</code><br />
* <code>summary</code><br />
* <code>max</code><br />
* <code>sqrt</code><br />
* <code>length</code> and <code>lengths</code></p>
<p>What happens when you run the following and why?</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="kw">mean</span>(ls1)
<span class="kw">sum</span>(ls1)</code></pre></div>
<p> </p>
</div>
</div>
<div id="exercise-2" class="section level1">
<h1>Exercise 2</h1>
<div id="filter-lists" class="section level2">
<h2>Filter lists</h2>
<p><code>pluck</code> Select an element by name or index<br />
<code>keep</code> Select elements that pass a logical test<br />
<code>discard</code> Select elements that do not pass a logical test<br />
<code>compact</code> Drop empty elements</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="kw">pluck</span>(ls1, <span class="dv">3</span>) <span class="co"># advantage = returns numeric </span>
ls1[<span class="dv">3</span>][[<span class="dv">1</span>]] <span class="co"># this is the same as above</span>
func <-<span class="st"> </span><span class="kw">map</span>(ls1, mean) <span class="op">></span><span class="st"> </span><span class="dv">10</span> <span class="co"># create a logical test (a predicate function) </span>
<span class="kw">keep</span>(ls1, func)
<span class="kw">discard</span>(ls1, func)
ls2 <-<span class="st"> </span><span class="kw">list</span>(<span class="dv">1</span>, <span class="ot">NA</span>, <span class="ot">NULL</span>, <span class="kw">integer</span>(<span class="dv">0</span>), <span class="kw">list</span>()) <span class="co"># list of empty and null things </span>
<span class="kw">compact</span>(ls2)</code></pre></div>
<p>Store plots in lists for easy retrieval. Create two plots of the <code>ls1</code> data (called <code>ls1p</code> and <code>ls2p</code>) and store in a list called <code>plot_list</code>.<br />
</p>
<p>First turn the list into a dataframe so <code>ggplot</code> understands it.</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">ls1_df <-<span class="st"> </span>ls1 <span class="op">%>%</span><span class="st"> </span>data.frame
<span class="kw">names</span>(ls1_df) <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"A"</span>, <span class="st">"B"</span>, <span class="st">"C"</span>)</code></pre></div>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">plot_list <-<span class="st"> </span><span class="kw">list</span>(ls1p, ls2p)</code></pre></div>
<p>Plot your plot from the object <code>plot_list</code><br />
<img src="Lesson6_files/figure-html/unnamed-chunk-12-1.png" width="672" /></p>
</div>
</div>
<div id="exercise-3" class="section level1">
<h1>Exercise 3</h1>
<div id="summarise-lists" class="section level2">
<h2>Summarise lists</h2>
<p><code>every</code> Do all elements pass a test?<br />
<code>some</code> Do some elements pass a test?<br />
<code>has_element</code> Does a list contain an element?<br />
<code>detect</code> Find first element to pass<br />
<code>detect_index</code> Find index of first element to pass<br />
<code>vec_depth</code> Return depth (number of levels of indexes)</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">ls1 <span class="op">%>%</span><span class="st"> </span><span class="kw">every</span>(is.character)
ls1 <span class="op">%>%</span><span class="st"> </span><span class="kw">some</span>(is.character)
ls1 <span class="op">%>%</span><span class="st"> </span><span class="kw">has_element</span>(<span class="st">"foo"</span>)
ls1 <span class="op">%>%</span><span class="st"> </span><span class="kw">detect</span>(is.character)
ls1 <span class="op">%>%</span><span class="st"> </span><span class="kw">detect_index</span>(is.character)
ls1 <span class="op">%>%</span><span class="st"> </span>vec_depth</code></pre></div>
</div>
</div>
<div id="exercise-4" class="section level1">
<h1>Exercise 4</h1>
<div id="transform-lists" class="section level2">
<h2>Transform lists</h2>
<p><code>modify</code> Apply function to each element<br />
<code>modify_at</code> Apply function to elements by name or index<br />
<code>modify_if</code> Apply function to elements that pass a test<br />
<code>modify_depth</code> Apply function to each element at a given level of a list</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">ls1_repeat <-<span class="st"> </span><span class="kw">list</span>(<span class="kw">list</span>(<span class="kw">list</span>(ls1))) <span class="co"># create list of lists </span>
ls1_repeat <span class="op">%>%</span><span class="st"> </span><span class="kw">map</span>(mean) <span class="co"># list is indexed too far down </span>
ls1_repeat <span class="op">%>%</span><span class="st"> </span><span class="kw">modify_depth</span>(<span class="dv">4</span>, mean) <span class="co"># access deep list indices </span></code></pre></div>
</div>
</div>
<div id="further-useful-purrr-functions" class="section level1">
<h1>Further useful <code>purrr</code> functions</h1>
<p><code>pmap</code> Apply a function to groups of elements from lists of lists<br />
<code>lmap</code> Apply function to each list-element of a list or vector<br />
<code>imap</code> Apply function to each element of a list or vector and its index</p>
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