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<h1 class="title"><span class="chapter-number">6</span> <span class="chapter-title">Summarizing data</span></h1>
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</header>
<section id="learning-objectives" class="level2" data-number="6.1">
<h2 data-number="6.1" class="anchored" data-anchor-id="learning-objectives"><span class="header-section-number">6.1</span> Learning objectives</h2>
<ul>
<li>Frequency tables</li>
<li>Descriptive statistics</li>
</ul>
</section>
<section id="introduction" class="level2" data-number="6.2">
<h2 data-number="6.2" class="anchored" data-anchor-id="introduction"><span class="header-section-number">6.2</span> Introduction</h2>
<p>In this chapter, we use numbers and tables to summarize our dataset. These summaries can sometimes suffice to fulfill the goals of our analysis when these goals are descriptive. The summaries also help us (and our readers) get to know more about our data and help us ensure that our data is adequate to perform the intended analyses. First we will consider what types of variables we have in our dataset (this is related, but not the same as the R data types), and then we will go through the process of generating useful summaries for variables of different types.</p>
</section>
<section id="types-of-variable" class="level2" data-number="6.3">
<h2 data-number="6.3" class="anchored" data-anchor-id="types-of-variable"><span class="header-section-number">6.3</span> Types of variable</h2>
<section id="categorical-variable" class="level3" data-number="6.3.1">
<h3 data-number="6.3.1" class="anchored" data-anchor-id="categorical-variable"><span class="header-section-number">6.3.1</span> Categorical variable</h3>
<p>Categorical variables are groups or categories. They can be represented by characters or numbers</p>
<ul>
<li><p><strong>Nominal</strong> variables represent categories or groups (e.g., gender, occupation, course, programs, university) and where there is no logical order between the different categories.</p></li>
<li><p><strong>Ordinal</strong> variables represent categories or groups that have a logical order (e.g., age groups)</p></li>
</ul>
</section>
<section id="numerical-variables" class="level3" data-number="6.3.2">
<h3 data-number="6.3.2" class="anchored" data-anchor-id="numerical-variables"><span class="header-section-number">6.3.2</span> Numerical variables</h3>
<p>Numerical variables are represented by numbers</p>
<ul>
<li><p><strong>discrete</strong> numerical variables can only take a certain number of values (like the numbers on a die or the number of pets a person has). Another way to think about those is that they are things that can be <strong>counted</strong> (number of cars, number of students, number of pets).</p></li>
<li><p><strong>Continuous</strong> variables can be measured and can theoretically take any value (e.g., the weight or height of a person, the distance between two cities, a price). They are things that can be <strong>measured</strong>.</p></li>
</ul>
<div class="callout callout-style-default callout-warning callout-titled">
<div class="callout-header d-flex align-content-center">
<div class="callout-icon-container">
<i class="callout-icon"></i>
</div>
<div class="callout-title-container flex-fill">
Categories represented with numbers
</div>
</div>
<div class="callout-body-container callout-body">
<p>It is important to look at your data to understand what the values represent. Sometimes you may have groups that are represented with numbers. When deciding what type of statistical analysis is adequate for a given variable, you most likely will want to consider treating those variables as categorical and not numerical..</p>
</div>
</div>
<p>The following code creates a table that describes the variables included in the mpg dataset.</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb1"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">tibble</span>(</span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a> <span class="at">Variable =</span> <span class="fu">colnames</span>(mpg),</span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a> <span class="at">Type =</span> <span class="fu">c</span>(<span class="st">"Nominal"</span>,</span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a> <span class="st">"Nominal"</span>,</span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a> <span class="st">"Continuous"</span>,</span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a> <span class="st">"Discrete"</span>,</span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a> <span class="st">"Discrete"</span>,</span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a> <span class="st">"Nominal"</span>,</span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a> <span class="st">"Nominal"</span>,</span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a> <span class="st">"Continuous"</span>,</span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a> <span class="st">"Continuous"</span>,</span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a> <span class="st">"Nominal"</span>,</span>
<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a> <span class="st">"Nominal"</span>),</span>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a> <span class="at">Description =</span> <span class="fu">c</span>(<span class="st">"Manufacturer name"</span>,</span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a> <span class="st">"Model name"</span>,</span>
<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a> <span class="st">"Engine displacement, in litres"</span>,</span>
<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a> <span class="st">"Year of manufacture"</span>,</span>
<span id="cb1-18"><a href="#cb1-18" aria-hidden="true" tabindex="-1"></a> <span class="st">"Number of cylinders"</span>,</span>
<span id="cb1-19"><a href="#cb1-19" aria-hidden="true" tabindex="-1"></a> <span class="st">"Type of transmission"</span>,</span>
<span id="cb1-20"><a href="#cb1-20" aria-hidden="true" tabindex="-1"></a> <span class="st">"Type of drive train"</span>,</span>
<span id="cb1-21"><a href="#cb1-21" aria-hidden="true" tabindex="-1"></a> <span class="st">"City miles per gallon"</span>,</span>
<span id="cb1-22"><a href="#cb1-22" aria-hidden="true" tabindex="-1"></a> <span class="st">"Highway miles per gallon"</span>,</span>
<span id="cb1-23"><a href="#cb1-23" aria-hidden="true" tabindex="-1"></a> <span class="st">"Fuel type"</span>,</span>
<span id="cb1-24"><a href="#cb1-24" aria-hidden="true" tabindex="-1"></a> <span class="st">"Type of car"</span>)</span>
<span id="cb1-25"><a href="#cb1-25" aria-hidden="true" tabindex="-1"></a> ) <span class="sc">%>%</span> </span>
<span id="cb1-26"><a href="#cb1-26" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>(</span>
<span id="cb1-27"><a href="#cb1-27" aria-hidden="true" tabindex="-1"></a> <span class="at">caption =</span> <span class="st">"Variables in the mpg dataset."</span>,</span>
<span id="cb1-28"><a href="#cb1-28" aria-hidden="true" tabindex="-1"></a> <span class="at">align =</span> <span class="fu">c</span>(<span class="st">"l"</span>,<span class="st">"l"</span>,<span class="st">"l"</span>)</span>
<span id="cb1-29"><a href="#cb1-29" aria-hidden="true" tabindex="-1"></a> ) <span class="sc">%>%</span> </span>
<span id="cb1-30"><a href="#cb1-30" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<caption>Variables in the mpg dataset.</caption>
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">Variable</th>
<th style="text-align: left;" data-quarto-table-cell-role="th">Type</th>
<th style="text-align: left;" data-quarto-table-cell-role="th">Description</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">manufacturer</td>
<td style="text-align: left;">Nominal</td>
<td style="text-align: left;">Manufacturer name</td>
</tr>
<tr class="even">
<td style="text-align: left;">model</td>
<td style="text-align: left;">Nominal</td>
<td style="text-align: left;">Model name</td>
</tr>
<tr class="odd">
<td style="text-align: left;">displ</td>
<td style="text-align: left;">Continuous</td>
<td style="text-align: left;">Engine displacement, in litres</td>
</tr>
<tr class="even">
<td style="text-align: left;">year</td>
<td style="text-align: left;">Discrete</td>
<td style="text-align: left;">Year of manufacture</td>
</tr>
<tr class="odd">
<td style="text-align: left;">cyl</td>
<td style="text-align: left;">Discrete</td>
<td style="text-align: left;">Number of cylinders</td>
</tr>
<tr class="even">
<td style="text-align: left;">trans</td>
<td style="text-align: left;">Nominal</td>
<td style="text-align: left;">Type of transmission</td>
</tr>
<tr class="odd">
<td style="text-align: left;">drv</td>
<td style="text-align: left;">Nominal</td>
<td style="text-align: left;">Type of drive train</td>
</tr>
<tr class="even">
<td style="text-align: left;">cty</td>
<td style="text-align: left;">Continuous</td>
<td style="text-align: left;">City miles per gallon</td>
</tr>
<tr class="odd">
<td style="text-align: left;">hwy</td>
<td style="text-align: left;">Continuous</td>
<td style="text-align: left;">Highway miles per gallon</td>
</tr>
<tr class="even">
<td style="text-align: left;">fl</td>
<td style="text-align: left;">Nominal</td>
<td style="text-align: left;">Fuel type</td>
</tr>
<tr class="odd">
<td style="text-align: left;">class</td>
<td style="text-align: left;">Nominal</td>
<td style="text-align: left;">Type of car</td>
</tr>
</tbody>
</table>
</div>
</div>
</section>
</section>
<section id="summarizing-categorical-data" class="level2" data-number="6.4">
<h2 data-number="6.4" class="anchored" data-anchor-id="summarizing-categorical-data"><span class="header-section-number">6.4</span> Summarizing categorical data</h2>
<p>There is not a lot that you can do with a single categorical variable other than reporting the frequency (number) and relative frequency (percentage) of observations for each category.</p>
<section id="frequency" class="level3" data-number="6.4.1">
<h3 data-number="6.4.1" class="anchored" data-anchor-id="frequency"><span class="header-section-number">6.4.1</span> Frequency</h3>
<p>We can use the <code>summarize()</code> and <code>n()</code> functions of the dplyr package (included in the tidyverse) to create a table of frequencies for the manufacturer variable. the <code>group_by()</code> function specifies which categorical variable I want to summarize. If we don’t use the <code>group_by()</code> function, we obtain the number of observations (rows) in the whole tibble.</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb2"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a>mpg <span class="sc">%>%</span> </span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">group_by</span>(manufacturer) <span class="sc">%>%</span> </span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">summarize</span>(<span class="at">freq =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> <span class="co"># n() counts the number of observations for each group.</span></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>() <span class="sc">%>%</span> </span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">manufacturer</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">freq</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">audi</td>
<td style="text-align: right;">18</td>
</tr>
<tr class="even">
<td style="text-align: left;">chevrolet</td>
<td style="text-align: right;">19</td>
</tr>
<tr class="odd">
<td style="text-align: left;">dodge</td>
<td style="text-align: right;">37</td>
</tr>
<tr class="even">
<td style="text-align: left;">ford</td>
<td style="text-align: right;">25</td>
</tr>
<tr class="odd">
<td style="text-align: left;">honda</td>
<td style="text-align: right;">9</td>
</tr>
<tr class="even">
<td style="text-align: left;">hyundai</td>
<td style="text-align: right;">14</td>
</tr>
<tr class="odd">
<td style="text-align: left;">jeep</td>
<td style="text-align: right;">8</td>
</tr>
<tr class="even">
<td style="text-align: left;">land rover</td>
<td style="text-align: right;">4</td>
</tr>
<tr class="odd">
<td style="text-align: left;">lincoln</td>
<td style="text-align: right;">3</td>
</tr>
<tr class="even">
<td style="text-align: left;">mercury</td>
<td style="text-align: right;">4</td>
</tr>
<tr class="odd">
<td style="text-align: left;">nissan</td>
<td style="text-align: right;">13</td>
</tr>
<tr class="even">
<td style="text-align: left;">pontiac</td>
<td style="text-align: right;">5</td>
</tr>
<tr class="odd">
<td style="text-align: left;">subaru</td>
<td style="text-align: right;">14</td>
</tr>
<tr class="even">
<td style="text-align: left;">toyota</td>
<td style="text-align: right;">34</td>
</tr>
<tr class="odd">
<td style="text-align: left;">volkswagen</td>
<td style="text-align: right;">27</td>
</tr>
</tbody>
</table>
</div>
</div>
</section>
<section id="relative-frequency" class="level3" data-number="6.4.2">
<h3 data-number="6.4.2" class="anchored" data-anchor-id="relative-frequency"><span class="header-section-number">6.4.2</span> Relative frequency</h3>
<p>The relative frequency is simply the frequency represented as a percentage rather than count. It is obtained by first computing the frequency and then calculating the relative frequency by dividing each counts by the sum of the counts: <code>mutate(rel_freq = freq/sum(freq))</code>.</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb3"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a>mpg <span class="sc">%>%</span> </span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">group_by</span>(manufacturer) <span class="sc">%>%</span> </span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">summarize</span>(<span class="at">freq =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> <span class="co"># n() counts the number of observations for each group.</span></span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">rel_freq =</span> freq<span class="sc">/</span><span class="fu">sum</span>(freq)) <span class="sc">%>%</span> </span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>() <span class="sc">%>%</span> </span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">manufacturer</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">freq</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">rel_freq</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">audi</td>
<td style="text-align: right;">18</td>
<td style="text-align: right;">0.0769231</td>
</tr>
<tr class="even">
<td style="text-align: left;">chevrolet</td>
<td style="text-align: right;">19</td>
<td style="text-align: right;">0.0811966</td>
</tr>
<tr class="odd">
<td style="text-align: left;">dodge</td>
<td style="text-align: right;">37</td>
<td style="text-align: right;">0.1581197</td>
</tr>
<tr class="even">
<td style="text-align: left;">ford</td>
<td style="text-align: right;">25</td>
<td style="text-align: right;">0.1068376</td>
</tr>
<tr class="odd">
<td style="text-align: left;">honda</td>
<td style="text-align: right;">9</td>
<td style="text-align: right;">0.0384615</td>
</tr>
<tr class="even">
<td style="text-align: left;">hyundai</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">0.0598291</td>
</tr>
<tr class="odd">
<td style="text-align: left;">jeep</td>
<td style="text-align: right;">8</td>
<td style="text-align: right;">0.0341880</td>
</tr>
<tr class="even">
<td style="text-align: left;">land rover</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">0.0170940</td>
</tr>
<tr class="odd">
<td style="text-align: left;">lincoln</td>
<td style="text-align: right;">3</td>
<td style="text-align: right;">0.0128205</td>
</tr>
<tr class="even">
<td style="text-align: left;">mercury</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">0.0170940</td>
</tr>
<tr class="odd">
<td style="text-align: left;">nissan</td>
<td style="text-align: right;">13</td>
<td style="text-align: right;">0.0555556</td>
</tr>
<tr class="even">
<td style="text-align: left;">pontiac</td>
<td style="text-align: right;">5</td>
<td style="text-align: right;">0.0213675</td>
</tr>
<tr class="odd">
<td style="text-align: left;">subaru</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">0.0598291</td>
</tr>
<tr class="even">
<td style="text-align: left;">toyota</td>
<td style="text-align: right;">34</td>
<td style="text-align: right;">0.1452991</td>
</tr>
<tr class="odd">
<td style="text-align: left;">volkswagen</td>
<td style="text-align: right;">27</td>
<td style="text-align: right;">0.1153846</td>
</tr>
</tbody>
</table>
</div>
</div>
<section id="rounding-the-values" class="level4" data-number="6.4.2.1">
<h4 data-number="6.4.2.1" class="anchored" data-anchor-id="rounding-the-values"><span class="header-section-number">6.4.2.1</span> Rounding the values</h4>
<p>When we calculate the relative frequency, we obtain numbers with a lot of decimals. We can used the <code>round()</code> function to specify the number of decimals we want. The syntax is <code>round(value, number of decimals)</code>.</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb4"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a>mpg <span class="sc">%>%</span> </span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">group_by</span>(manufacturer) <span class="sc">%>%</span> </span>
<span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">summarize</span>(<span class="at">freq =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> <span class="co"># n() counts the number of observations for each group.</span></span>
<span id="cb4-4"><a href="#cb4-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">rel_freq =</span> <span class="fu">round</span>(freq<span class="sc">/</span><span class="fu">sum</span>(freq),<span class="dv">3</span>)) <span class="sc">%>%</span> </span>
<span id="cb4-5"><a href="#cb4-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>() <span class="sc">%>%</span> </span>
<span id="cb4-6"><a href="#cb4-6" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">manufacturer</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">freq</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">rel_freq</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">audi</td>
<td style="text-align: right;">18</td>
<td style="text-align: right;">0.077</td>
</tr>
<tr class="even">
<td style="text-align: left;">chevrolet</td>
<td style="text-align: right;">19</td>
<td style="text-align: right;">0.081</td>
</tr>
<tr class="odd">
<td style="text-align: left;">dodge</td>
<td style="text-align: right;">37</td>
<td style="text-align: right;">0.158</td>
</tr>
<tr class="even">
<td style="text-align: left;">ford</td>
<td style="text-align: right;">25</td>
<td style="text-align: right;">0.107</td>
</tr>
<tr class="odd">
<td style="text-align: left;">honda</td>
<td style="text-align: right;">9</td>
<td style="text-align: right;">0.038</td>
</tr>
<tr class="even">
<td style="text-align: left;">hyundai</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">0.060</td>
</tr>
<tr class="odd">
<td style="text-align: left;">jeep</td>
<td style="text-align: right;">8</td>
<td style="text-align: right;">0.034</td>
</tr>
<tr class="even">
<td style="text-align: left;">land rover</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">0.017</td>
</tr>
<tr class="odd">
<td style="text-align: left;">lincoln</td>
<td style="text-align: right;">3</td>
<td style="text-align: right;">0.013</td>
</tr>
<tr class="even">
<td style="text-align: left;">mercury</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">0.017</td>
</tr>
<tr class="odd">
<td style="text-align: left;">nissan</td>
<td style="text-align: right;">13</td>
<td style="text-align: right;">0.056</td>
</tr>
<tr class="even">
<td style="text-align: left;">pontiac</td>
<td style="text-align: right;">5</td>
<td style="text-align: right;">0.021</td>
</tr>
<tr class="odd">
<td style="text-align: left;">subaru</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">0.060</td>
</tr>
<tr class="even">
<td style="text-align: left;">toyota</td>
<td style="text-align: right;">34</td>
<td style="text-align: right;">0.145</td>
</tr>
<tr class="odd">
<td style="text-align: left;">volkswagen</td>
<td style="text-align: right;">27</td>
<td style="text-align: right;">0.115</td>
</tr>
</tbody>
</table>
</div>
</div>
</section>
<section id="converting-the-relative-frequency-to-percentages" class="level4" data-number="6.4.2.2">
<h4 data-number="6.4.2.2" class="anchored" data-anchor-id="converting-the-relative-frequency-to-percentages"><span class="header-section-number">6.4.2.2</span> Converting the relative frequency to percentages</h4>
<p>Another thing we might want to do is show the relative frequency as a percentage. This can be done by multiplying the relative frequency by 100.</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb5"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a>mpg <span class="sc">%>%</span> </span>
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">group_by</span>(manufacturer) <span class="sc">%>%</span> </span>
<span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">summarize</span>(<span class="at">freq =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> <span class="co"># n() counts the number of observations for each group.</span></span>
<span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">pct =</span> <span class="fu">round</span>(freq<span class="sc">/</span><span class="fu">sum</span>(freq)<span class="sc">*</span><span class="dv">100</span>,<span class="dv">1</span>)) <span class="sc">%>%</span> </span>
<span id="cb5-5"><a href="#cb5-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>() <span class="sc">%>%</span> </span>
<span id="cb5-6"><a href="#cb5-6" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">manufacturer</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">freq</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">pct</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">audi</td>
<td style="text-align: right;">18</td>
<td style="text-align: right;">7.7</td>
</tr>
<tr class="even">
<td style="text-align: left;">chevrolet</td>
<td style="text-align: right;">19</td>
<td style="text-align: right;">8.1</td>
</tr>
<tr class="odd">
<td style="text-align: left;">dodge</td>
<td style="text-align: right;">37</td>
<td style="text-align: right;">15.8</td>
</tr>
<tr class="even">
<td style="text-align: left;">ford</td>
<td style="text-align: right;">25</td>
<td style="text-align: right;">10.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">honda</td>
<td style="text-align: right;">9</td>
<td style="text-align: right;">3.8</td>
</tr>
<tr class="even">
<td style="text-align: left;">hyundai</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">6.0</td>
</tr>
<tr class="odd">
<td style="text-align: left;">jeep</td>
<td style="text-align: right;">8</td>
<td style="text-align: right;">3.4</td>
</tr>
<tr class="even">
<td style="text-align: left;">land rover</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">1.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">lincoln</td>
<td style="text-align: right;">3</td>
<td style="text-align: right;">1.3</td>
</tr>
<tr class="even">
<td style="text-align: left;">mercury</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">1.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">nissan</td>
<td style="text-align: right;">13</td>
<td style="text-align: right;">5.6</td>
</tr>
<tr class="even">
<td style="text-align: left;">pontiac</td>
<td style="text-align: right;">5</td>
<td style="text-align: right;">2.1</td>
</tr>
<tr class="odd">
<td style="text-align: left;">subaru</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">6.0</td>
</tr>
<tr class="even">
<td style="text-align: left;">toyota</td>
<td style="text-align: right;">34</td>
<td style="text-align: right;">14.5</td>
</tr>
<tr class="odd">
<td style="text-align: left;">volkswagen</td>
<td style="text-align: right;">27</td>
<td style="text-align: right;">11.5</td>
</tr>
</tbody>
</table>
</div>
</div>
</section>
<section id="ordering-the-categories" class="level4" data-number="6.4.2.3">
<h4 data-number="6.4.2.3" class="anchored" data-anchor-id="ordering-the-categories"><span class="header-section-number">6.4.2.3</span> Ordering the categories</h4>
<p>I can use <code>arrange()</code> to reorder my table using alphabetical order or frequency. The syntax of the arrange function is <code>arrange(x, variable to use for ordering)</code>. The variables are ordered in ascending order by default. To arrange your variable in descending order, you use <code>desc()</code> like this <code>arrange(x, desc(variable to use for ordering))</code> . You can use arrange with numeric values or characters.</p>
<section id="order-by-frequency-ascending" class="level5" data-number="6.4.2.3.1">
<h5 data-number="6.4.2.3.1" class="anchored" data-anchor-id="order-by-frequency-ascending"><span class="header-section-number">6.4.2.3.1</span> Order by frequency (ascending)</h5>
<div class="cell">
<div class="sourceCode cell-code" id="cb6"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a>mpg <span class="sc">%>%</span> </span>
<span id="cb6-2"><a href="#cb6-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">group_by</span>(manufacturer) <span class="sc">%>%</span> </span>
<span id="cb6-3"><a href="#cb6-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">summarize</span>(<span class="at">freq =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> <span class="co"># n() counts the number of observations for each group.</span></span>
<span id="cb6-4"><a href="#cb6-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">pct =</span> <span class="fu">round</span>(freq<span class="sc">/</span><span class="fu">sum</span>(freq)<span class="sc">*</span><span class="dv">100</span>,<span class="dv">1</span>)) <span class="sc">%>%</span> </span>
<span id="cb6-5"><a href="#cb6-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">arrange</span>(freq) <span class="sc">%>%</span> </span>
<span id="cb6-6"><a href="#cb6-6" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>() <span class="sc">%>%</span> </span>
<span id="cb6-7"><a href="#cb6-7" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">manufacturer</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">freq</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">pct</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">lincoln</td>
<td style="text-align: right;">3</td>
<td style="text-align: right;">1.3</td>
</tr>
<tr class="even">
<td style="text-align: left;">land rover</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">1.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">mercury</td>
<td style="text-align: right;">4</td>
<td style="text-align: right;">1.7</td>
</tr>
<tr class="even">
<td style="text-align: left;">pontiac</td>
<td style="text-align: right;">5</td>
<td style="text-align: right;">2.1</td>
</tr>
<tr class="odd">
<td style="text-align: left;">jeep</td>
<td style="text-align: right;">8</td>
<td style="text-align: right;">3.4</td>
</tr>
<tr class="even">
<td style="text-align: left;">honda</td>
<td style="text-align: right;">9</td>
<td style="text-align: right;">3.8</td>
</tr>
<tr class="odd">
<td style="text-align: left;">nissan</td>
<td style="text-align: right;">13</td>
<td style="text-align: right;">5.6</td>
</tr>
<tr class="even">
<td style="text-align: left;">hyundai</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">6.0</td>
</tr>
<tr class="odd">
<td style="text-align: left;">subaru</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">6.0</td>
</tr>
<tr class="even">
<td style="text-align: left;">audi</td>
<td style="text-align: right;">18</td>
<td style="text-align: right;">7.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">chevrolet</td>
<td style="text-align: right;">19</td>
<td style="text-align: right;">8.1</td>
</tr>
<tr class="even">
<td style="text-align: left;">ford</td>
<td style="text-align: right;">25</td>
<td style="text-align: right;">10.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">volkswagen</td>
<td style="text-align: right;">27</td>
<td style="text-align: right;">11.5</td>
</tr>
<tr class="even">
<td style="text-align: left;">toyota</td>
<td style="text-align: right;">34</td>
<td style="text-align: right;">14.5</td>
</tr>
<tr class="odd">
<td style="text-align: left;">dodge</td>
<td style="text-align: right;">37</td>
<td style="text-align: right;">15.8</td>
</tr>
</tbody>
</table>
</div>
</div>
</section>
<section id="order-by-frequency-decreasing" class="level5" data-number="6.4.2.3.2">
<h5 data-number="6.4.2.3.2" class="anchored" data-anchor-id="order-by-frequency-decreasing"><span class="header-section-number">6.4.2.3.2</span> Order by frequency (decreasing)</h5>
<div class="cell">
<div class="sourceCode cell-code" id="cb7"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a>mpg <span class="sc">%>%</span> </span>
<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">group_by</span>(manufacturer) <span class="sc">%>%</span> </span>
<span id="cb7-3"><a href="#cb7-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">summarize</span>(<span class="at">freq =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> <span class="co"># n() counts the number of observations for each group.</span></span>
<span id="cb7-4"><a href="#cb7-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">pct =</span> <span class="fu">round</span>(freq<span class="sc">/</span><span class="fu">sum</span>(freq)<span class="sc">*</span><span class="dv">100</span>,<span class="dv">1</span>)) <span class="sc">%>%</span> </span>
<span id="cb7-5"><a href="#cb7-5" aria-hidden="true" tabindex="-1"></a> <span class="fu">arrange</span>(<span class="fu">desc</span>(freq)) <span class="sc">%>%</span> </span>
<span id="cb7-6"><a href="#cb7-6" aria-hidden="true" tabindex="-1"></a> <span class="fu">kbl</span>() <span class="sc">%>%</span> </span>
<span id="cb7-7"><a href="#cb7-7" aria-hidden="true" tabindex="-1"></a> <span class="fu">kable_classic</span>()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="cell-output-display">
<table class="lightable-classic table table-sm table-striped small" data-quarto-postprocess="true">
<thead>
<tr class="header">
<th style="text-align: left;" data-quarto-table-cell-role="th">manufacturer</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">freq</th>
<th style="text-align: right;" data-quarto-table-cell-role="th">pct</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: left;">dodge</td>
<td style="text-align: right;">37</td>
<td style="text-align: right;">15.8</td>
</tr>
<tr class="even">
<td style="text-align: left;">toyota</td>
<td style="text-align: right;">34</td>
<td style="text-align: right;">14.5</td>
</tr>
<tr class="odd">
<td style="text-align: left;">volkswagen</td>
<td style="text-align: right;">27</td>
<td style="text-align: right;">11.5</td>
</tr>
<tr class="even">
<td style="text-align: left;">ford</td>
<td style="text-align: right;">25</td>
<td style="text-align: right;">10.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">chevrolet</td>
<td style="text-align: right;">19</td>
<td style="text-align: right;">8.1</td>
</tr>
<tr class="even">
<td style="text-align: left;">audi</td>
<td style="text-align: right;">18</td>
<td style="text-align: right;">7.7</td>
</tr>
<tr class="odd">
<td style="text-align: left;">hyundai</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">6.0</td>
</tr>
<tr class="even">
<td style="text-align: left;">subaru</td>
<td style="text-align: right;">14</td>
<td style="text-align: right;">6.0</td>
</tr>
<tr class="odd">
<td style="text-align: left;">nissan</td>
<td style="text-align: right;">13</td>
<td style="text-align: right;">5.6</td>
</tr>
<tr class="even">
<td style="text-align: left;">honda</td>
<td style="text-align: right;">9</td>
<td style="text-align: right;">3.8</td>
</tr>
<tr class="odd">
<td style="text-align: left;">jeep</td>
<td style="text-align: right;">8</td>
<td style="text-align: right;">3.4</td>
</tr>
<tr class="even">