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<body>
<h1 class="title toc-ignore">Grouped data</h1>
<p>dplyr verbs are particularly powerful when you apply them to grouped
data frames (<code>grouped_df</code> objects). This vignette shows
you:</p>
<ul>
<li><p>How to group, inspect, and ungroup with <code>group_by()</code>
and friends.</p></li>
<li><p>How individual dplyr verbs changes their behaviour when applied
to grouped data frame.</p></li>
<li><p>How to access data about the “current” group from within a
verb.</p></li>
</ul>
<p>We’ll start by loading dplyr:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" tabindex="-1"></a><span class="fu">library</span>(dplyr)</span></code></pre></div>
<div id="group_by" class="section level2">
<h2><code>group_by()</code></h2>
<p>The most important grouping verb is <code>group_by()</code>: it takes
a data frame and one or more variables to group by:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb2-1"><a href="#cb2-1" tabindex="-1"></a>by_species <span class="ot"><-</span> starwars <span class="sc">%>%</span> <span class="fu">group_by</span>(species)</span>
<span id="cb2-2"><a href="#cb2-2" tabindex="-1"></a>by_sex_gender <span class="ot"><-</span> starwars <span class="sc">%>%</span> <span class="fu">group_by</span>(sex, gender)</span></code></pre></div>
<p>You can see the grouping when you print the data:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1" tabindex="-1"></a>by_species</span>
<span id="cb3-2"><a href="#cb3-2" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 14</span></span>
<span id="cb3-3"><a href="#cb3-3" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb3-4"><a href="#cb3-4" tabindex="-1"></a><span class="co">#> name height mass hair_color skin_color eye_color birth_year sex gender</span></span>
<span id="cb3-5"><a href="#cb3-5" tabindex="-1"></a><span class="co">#> <chr> <int> <dbl> <chr> <chr> <chr> <dbl> <chr> <chr> </span></span>
<span id="cb3-6"><a href="#cb3-6" tabindex="-1"></a><span class="co">#> 1 Luke Sky… 172 77 blond fair blue 19 male mascu…</span></span>
<span id="cb3-7"><a href="#cb3-7" tabindex="-1"></a><span class="co">#> 2 C-3PO 167 75 <NA> gold yellow 112 none mascu…</span></span>
<span id="cb3-8"><a href="#cb3-8" tabindex="-1"></a><span class="co">#> 3 R2-D2 96 32 <NA> white, bl… red 33 none mascu…</span></span>
<span id="cb3-9"><a href="#cb3-9" tabindex="-1"></a><span class="co">#> 4 Darth Va… 202 136 none white yellow 41.9 male mascu…</span></span>
<span id="cb3-10"><a href="#cb3-10" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span>
<span id="cb3-11"><a href="#cb3-11" tabindex="-1"></a><span class="co">#> # ℹ 5 more variables: homeworld <chr>, species <chr>, films <list>,</span></span>
<span id="cb3-12"><a href="#cb3-12" tabindex="-1"></a><span class="co">#> # vehicles <list>, starships <list></span></span>
<span id="cb3-13"><a href="#cb3-13" tabindex="-1"></a>by_sex_gender</span>
<span id="cb3-14"><a href="#cb3-14" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 14</span></span>
<span id="cb3-15"><a href="#cb3-15" tabindex="-1"></a><span class="co">#> # Groups: sex, gender [6]</span></span>
<span id="cb3-16"><a href="#cb3-16" tabindex="-1"></a><span class="co">#> name height mass hair_color skin_color eye_color birth_year sex gender</span></span>
<span id="cb3-17"><a href="#cb3-17" tabindex="-1"></a><span class="co">#> <chr> <int> <dbl> <chr> <chr> <chr> <dbl> <chr> <chr> </span></span>
<span id="cb3-18"><a href="#cb3-18" tabindex="-1"></a><span class="co">#> 1 Luke Sky… 172 77 blond fair blue 19 male mascu…</span></span>
<span id="cb3-19"><a href="#cb3-19" tabindex="-1"></a><span class="co">#> 2 C-3PO 167 75 <NA> gold yellow 112 none mascu…</span></span>
<span id="cb3-20"><a href="#cb3-20" tabindex="-1"></a><span class="co">#> 3 R2-D2 96 32 <NA> white, bl… red 33 none mascu…</span></span>
<span id="cb3-21"><a href="#cb3-21" tabindex="-1"></a><span class="co">#> 4 Darth Va… 202 136 none white yellow 41.9 male mascu…</span></span>
<span id="cb3-22"><a href="#cb3-22" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span>
<span id="cb3-23"><a href="#cb3-23" tabindex="-1"></a><span class="co">#> # ℹ 5 more variables: homeworld <chr>, species <chr>, films <list>,</span></span>
<span id="cb3-24"><a href="#cb3-24" tabindex="-1"></a><span class="co">#> # vehicles <list>, starships <list></span></span></code></pre></div>
<p>Or use <code>tally()</code> to count the number of rows in each
group. The <code>sort</code> argument is useful if you want to see the
largest groups up front.</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb4-1"><a href="#cb4-1" tabindex="-1"></a>by_species <span class="sc">%>%</span> <span class="fu">tally</span>()</span>
<span id="cb4-2"><a href="#cb4-2" tabindex="-1"></a><span class="co">#> # A tibble: 38 × 2</span></span>
<span id="cb4-3"><a href="#cb4-3" tabindex="-1"></a><span class="co">#> species n</span></span>
<span id="cb4-4"><a href="#cb4-4" tabindex="-1"></a><span class="co">#> <chr> <int></span></span>
<span id="cb4-5"><a href="#cb4-5" tabindex="-1"></a><span class="co">#> 1 Aleena 1</span></span>
<span id="cb4-6"><a href="#cb4-6" tabindex="-1"></a><span class="co">#> 2 Besalisk 1</span></span>
<span id="cb4-7"><a href="#cb4-7" tabindex="-1"></a><span class="co">#> 3 Cerean 1</span></span>
<span id="cb4-8"><a href="#cb4-8" tabindex="-1"></a><span class="co">#> 4 Chagrian 1</span></span>
<span id="cb4-9"><a href="#cb4-9" tabindex="-1"></a><span class="co">#> # ℹ 34 more rows</span></span>
<span id="cb4-10"><a href="#cb4-10" tabindex="-1"></a></span>
<span id="cb4-11"><a href="#cb4-11" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> <span class="fu">tally</span>(<span class="at">sort =</span> <span class="cn">TRUE</span>)</span>
<span id="cb4-12"><a href="#cb4-12" tabindex="-1"></a><span class="co">#> # A tibble: 6 × 3</span></span>
<span id="cb4-13"><a href="#cb4-13" tabindex="-1"></a><span class="co">#> # Groups: sex [5]</span></span>
<span id="cb4-14"><a href="#cb4-14" tabindex="-1"></a><span class="co">#> sex gender n</span></span>
<span id="cb4-15"><a href="#cb4-15" tabindex="-1"></a><span class="co">#> <chr> <chr> <int></span></span>
<span id="cb4-16"><a href="#cb4-16" tabindex="-1"></a><span class="co">#> 1 male masculine 60</span></span>
<span id="cb4-17"><a href="#cb4-17" tabindex="-1"></a><span class="co">#> 2 female feminine 16</span></span>
<span id="cb4-18"><a href="#cb4-18" tabindex="-1"></a><span class="co">#> 3 none masculine 5</span></span>
<span id="cb4-19"><a href="#cb4-19" tabindex="-1"></a><span class="co">#> 4 <NA> <NA> 4</span></span>
<span id="cb4-20"><a href="#cb4-20" tabindex="-1"></a><span class="co">#> # ℹ 2 more rows</span></span></code></pre></div>
<p>As well as grouping by existing variables, you can group by any
function of existing variables. This is equivalent to performing a
<code>mutate()</code> <strong>before</strong> the
<code>group_by()</code>:</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb5-1"><a href="#cb5-1" tabindex="-1"></a>bmi_breaks <span class="ot"><-</span> <span class="fu">c</span>(<span class="dv">0</span>, <span class="fl">18.5</span>, <span class="dv">25</span>, <span class="dv">30</span>, <span class="cn">Inf</span>)</span>
<span id="cb5-2"><a href="#cb5-2" tabindex="-1"></a></span>
<span id="cb5-3"><a href="#cb5-3" tabindex="-1"></a>starwars <span class="sc">%>%</span></span>
<span id="cb5-4"><a href="#cb5-4" tabindex="-1"></a> <span class="fu">group_by</span>(<span class="at">bmi_cat =</span> <span class="fu">cut</span>(mass<span class="sc">/</span>(height<span class="sc">/</span><span class="dv">100</span>)<span class="sc">^</span><span class="dv">2</span>, <span class="at">breaks=</span>bmi_breaks)) <span class="sc">%>%</span></span>
<span id="cb5-5"><a href="#cb5-5" tabindex="-1"></a> <span class="fu">tally</span>()</span>
<span id="cb5-6"><a href="#cb5-6" tabindex="-1"></a><span class="co">#> # A tibble: 5 × 2</span></span>
<span id="cb5-7"><a href="#cb5-7" tabindex="-1"></a><span class="co">#> bmi_cat n</span></span>
<span id="cb5-8"><a href="#cb5-8" tabindex="-1"></a><span class="co">#> <fct> <int></span></span>
<span id="cb5-9"><a href="#cb5-9" tabindex="-1"></a><span class="co">#> 1 (0,18.5] 10</span></span>
<span id="cb5-10"><a href="#cb5-10" tabindex="-1"></a><span class="co">#> 2 (18.5,25] 24</span></span>
<span id="cb5-11"><a href="#cb5-11" tabindex="-1"></a><span class="co">#> 3 (25,30] 13</span></span>
<span id="cb5-12"><a href="#cb5-12" tabindex="-1"></a><span class="co">#> 4 (30,Inf] 12</span></span>
<span id="cb5-13"><a href="#cb5-13" tabindex="-1"></a><span class="co">#> # ℹ 1 more row</span></span></code></pre></div>
</div>
<div id="group-metadata" class="section level2">
<h2>Group metadata</h2>
<p>You can see underlying group data with <code>group_keys()</code>. It
has one row for each group and one column for each grouping
variable:</p>
<div class="sourceCode" id="cb6"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb6-1"><a href="#cb6-1" tabindex="-1"></a>by_species <span class="sc">%>%</span> <span class="fu">group_keys</span>()</span>
<span id="cb6-2"><a href="#cb6-2" tabindex="-1"></a><span class="co">#> # A tibble: 38 × 1</span></span>
<span id="cb6-3"><a href="#cb6-3" tabindex="-1"></a><span class="co">#> species </span></span>
<span id="cb6-4"><a href="#cb6-4" tabindex="-1"></a><span class="co">#> <chr> </span></span>
<span id="cb6-5"><a href="#cb6-5" tabindex="-1"></a><span class="co">#> 1 Aleena </span></span>
<span id="cb6-6"><a href="#cb6-6" tabindex="-1"></a><span class="co">#> 2 Besalisk</span></span>
<span id="cb6-7"><a href="#cb6-7" tabindex="-1"></a><span class="co">#> 3 Cerean </span></span>
<span id="cb6-8"><a href="#cb6-8" tabindex="-1"></a><span class="co">#> 4 Chagrian</span></span>
<span id="cb6-9"><a href="#cb6-9" tabindex="-1"></a><span class="co">#> # ℹ 34 more rows</span></span>
<span id="cb6-10"><a href="#cb6-10" tabindex="-1"></a></span>
<span id="cb6-11"><a href="#cb6-11" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> <span class="fu">group_keys</span>()</span>
<span id="cb6-12"><a href="#cb6-12" tabindex="-1"></a><span class="co">#> # A tibble: 6 × 2</span></span>
<span id="cb6-13"><a href="#cb6-13" tabindex="-1"></a><span class="co">#> sex gender </span></span>
<span id="cb6-14"><a href="#cb6-14" tabindex="-1"></a><span class="co">#> <chr> <chr> </span></span>
<span id="cb6-15"><a href="#cb6-15" tabindex="-1"></a><span class="co">#> 1 female feminine </span></span>
<span id="cb6-16"><a href="#cb6-16" tabindex="-1"></a><span class="co">#> 2 hermaphroditic masculine</span></span>
<span id="cb6-17"><a href="#cb6-17" tabindex="-1"></a><span class="co">#> 3 male masculine</span></span>
<span id="cb6-18"><a href="#cb6-18" tabindex="-1"></a><span class="co">#> 4 none feminine </span></span>
<span id="cb6-19"><a href="#cb6-19" tabindex="-1"></a><span class="co">#> # ℹ 2 more rows</span></span></code></pre></div>
<p>You can see which group each row belongs to with
<code>group_indices()</code>:</p>
<div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1" tabindex="-1"></a>by_species <span class="sc">%>%</span> <span class="fu">group_indices</span>()</span>
<span id="cb7-2"><a href="#cb7-2" tabindex="-1"></a><span class="co">#> [1] 11 6 6 11 11 11 11 6 11 11 11 11 34 11 24 12 11 38 36 11 11 6 31 11 11</span></span>
<span id="cb7-3"><a href="#cb7-3" tabindex="-1"></a><span class="co">#> [26] 18 11 11 8 26 11 21 11 11 10 10 10 11 30 7 11 11 37 32 32 1 33 35 29 11</span></span>
<span id="cb7-4"><a href="#cb7-4" tabindex="-1"></a><span class="co">#> [51] 3 20 37 27 13 23 16 4 38 38 11 9 17 17 11 11 11 11 5 2 15 15 11 6 25</span></span>
<span id="cb7-5"><a href="#cb7-5" tabindex="-1"></a><span class="co">#> [76] 19 28 14 34 11 38 22 11 11 11 6 11</span></span></code></pre></div>
<p>And which rows each group contains with
<code>group_rows()</code>:</p>
<div class="sourceCode" id="cb8"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb8-1"><a href="#cb8-1" tabindex="-1"></a>by_species <span class="sc">%>%</span> <span class="fu">group_rows</span>() <span class="sc">%>%</span> <span class="fu">head</span>()</span>
<span id="cb8-2"><a href="#cb8-2" tabindex="-1"></a><span class="co">#> <list_of<integer>[6]></span></span>
<span id="cb8-3"><a href="#cb8-3" tabindex="-1"></a><span class="co">#> [[1]]</span></span>
<span id="cb8-4"><a href="#cb8-4" tabindex="-1"></a><span class="co">#> [1] 46</span></span>
<span id="cb8-5"><a href="#cb8-5" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb8-6"><a href="#cb8-6" tabindex="-1"></a><span class="co">#> [[2]]</span></span>
<span id="cb8-7"><a href="#cb8-7" tabindex="-1"></a><span class="co">#> [1] 70</span></span>
<span id="cb8-8"><a href="#cb8-8" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb8-9"><a href="#cb8-9" tabindex="-1"></a><span class="co">#> [[3]]</span></span>
<span id="cb8-10"><a href="#cb8-10" tabindex="-1"></a><span class="co">#> [1] 51</span></span>
<span id="cb8-11"><a href="#cb8-11" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb8-12"><a href="#cb8-12" tabindex="-1"></a><span class="co">#> [[4]]</span></span>
<span id="cb8-13"><a href="#cb8-13" tabindex="-1"></a><span class="co">#> [1] 58</span></span>
<span id="cb8-14"><a href="#cb8-14" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb8-15"><a href="#cb8-15" tabindex="-1"></a><span class="co">#> [[5]]</span></span>
<span id="cb8-16"><a href="#cb8-16" tabindex="-1"></a><span class="co">#> [1] 69</span></span>
<span id="cb8-17"><a href="#cb8-17" tabindex="-1"></a><span class="co">#> </span></span>
<span id="cb8-18"><a href="#cb8-18" tabindex="-1"></a><span class="co">#> [[6]]</span></span>
<span id="cb8-19"><a href="#cb8-19" tabindex="-1"></a><span class="co">#> [1] 2 3 8 22 74 86</span></span></code></pre></div>
<p>Use <code>group_vars()</code> if you just want the names of the
grouping variables:</p>
<div class="sourceCode" id="cb9"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb9-1"><a href="#cb9-1" tabindex="-1"></a>by_species <span class="sc">%>%</span> <span class="fu">group_vars</span>()</span>
<span id="cb9-2"><a href="#cb9-2" tabindex="-1"></a><span class="co">#> [1] "species"</span></span>
<span id="cb9-3"><a href="#cb9-3" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> <span class="fu">group_vars</span>()</span>
<span id="cb9-4"><a href="#cb9-4" tabindex="-1"></a><span class="co">#> [1] "sex" "gender"</span></span></code></pre></div>
<div id="changing-and-adding-to-grouping-variables" class="section level3">
<h3>Changing and adding to grouping variables</h3>
<p>If you apply <code>group_by()</code> to an already grouped dataset,
will overwrite the existing grouping variables. For example, the
following code groups by <code>homeworld</code> instead of
<code>species</code>:</p>
<div class="sourceCode" id="cb10"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb10-1"><a href="#cb10-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb10-2"><a href="#cb10-2" tabindex="-1"></a> <span class="fu">group_by</span>(homeworld) <span class="sc">%>%</span></span>
<span id="cb10-3"><a href="#cb10-3" tabindex="-1"></a> <span class="fu">tally</span>()</span>
<span id="cb10-4"><a href="#cb10-4" tabindex="-1"></a><span class="co">#> # A tibble: 49 × 2</span></span>
<span id="cb10-5"><a href="#cb10-5" tabindex="-1"></a><span class="co">#> homeworld n</span></span>
<span id="cb10-6"><a href="#cb10-6" tabindex="-1"></a><span class="co">#> <chr> <int></span></span>
<span id="cb10-7"><a href="#cb10-7" tabindex="-1"></a><span class="co">#> 1 Alderaan 3</span></span>
<span id="cb10-8"><a href="#cb10-8" tabindex="-1"></a><span class="co">#> 2 Aleen Minor 1</span></span>
<span id="cb10-9"><a href="#cb10-9" tabindex="-1"></a><span class="co">#> 3 Bespin 1</span></span>
<span id="cb10-10"><a href="#cb10-10" tabindex="-1"></a><span class="co">#> 4 Bestine IV 1</span></span>
<span id="cb10-11"><a href="#cb10-11" tabindex="-1"></a><span class="co">#> # ℹ 45 more rows</span></span></code></pre></div>
<p>To <strong>augment</strong> the grouping, using
<code>.add = TRUE</code><a href="#fn1" class="footnote-ref" id="fnref1"><sup>1</sup></a>. For example, the following code groups by
species and homeworld:</p>
<div class="sourceCode" id="cb11"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb11-1"><a href="#cb11-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb11-2"><a href="#cb11-2" tabindex="-1"></a> <span class="fu">group_by</span>(homeworld, <span class="at">.add =</span> <span class="cn">TRUE</span>) <span class="sc">%>%</span></span>
<span id="cb11-3"><a href="#cb11-3" tabindex="-1"></a> <span class="fu">tally</span>()</span>
<span id="cb11-4"><a href="#cb11-4" tabindex="-1"></a><span class="co">#> # A tibble: 57 × 3</span></span>
<span id="cb11-5"><a href="#cb11-5" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb11-6"><a href="#cb11-6" tabindex="-1"></a><span class="co">#> species homeworld n</span></span>
<span id="cb11-7"><a href="#cb11-7" tabindex="-1"></a><span class="co">#> <chr> <chr> <int></span></span>
<span id="cb11-8"><a href="#cb11-8" tabindex="-1"></a><span class="co">#> 1 Aleena Aleen Minor 1</span></span>
<span id="cb11-9"><a href="#cb11-9" tabindex="-1"></a><span class="co">#> 2 Besalisk Ojom 1</span></span>
<span id="cb11-10"><a href="#cb11-10" tabindex="-1"></a><span class="co">#> 3 Cerean Cerea 1</span></span>
<span id="cb11-11"><a href="#cb11-11" tabindex="-1"></a><span class="co">#> 4 Chagrian Champala 1</span></span>
<span id="cb11-12"><a href="#cb11-12" tabindex="-1"></a><span class="co">#> # ℹ 53 more rows</span></span></code></pre></div>
</div>
<div id="removing-grouping-variables" class="section level3">
<h3>Removing grouping variables</h3>
<p>To remove all grouping variables, use <code>ungroup()</code>:</p>
<div class="sourceCode" id="cb12"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb12-1"><a href="#cb12-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb12-2"><a href="#cb12-2" tabindex="-1"></a> <span class="fu">ungroup</span>() <span class="sc">%>%</span></span>
<span id="cb12-3"><a href="#cb12-3" tabindex="-1"></a> <span class="fu">tally</span>()</span>
<span id="cb12-4"><a href="#cb12-4" tabindex="-1"></a><span class="co">#> # A tibble: 1 × 1</span></span>
<span id="cb12-5"><a href="#cb12-5" tabindex="-1"></a><span class="co">#> n</span></span>
<span id="cb12-6"><a href="#cb12-6" tabindex="-1"></a><span class="co">#> <int></span></span>
<span id="cb12-7"><a href="#cb12-7" tabindex="-1"></a><span class="co">#> 1 87</span></span></code></pre></div>
<p>You can also choose to selectively ungroup by listing the variables
you want to remove:</p>
<div class="sourceCode" id="cb13"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb13-1"><a href="#cb13-1" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> </span>
<span id="cb13-2"><a href="#cb13-2" tabindex="-1"></a> <span class="fu">ungroup</span>(sex) <span class="sc">%>%</span> </span>
<span id="cb13-3"><a href="#cb13-3" tabindex="-1"></a> <span class="fu">tally</span>()</span>
<span id="cb13-4"><a href="#cb13-4" tabindex="-1"></a><span class="co">#> # A tibble: 3 × 2</span></span>
<span id="cb13-5"><a href="#cb13-5" tabindex="-1"></a><span class="co">#> gender n</span></span>
<span id="cb13-6"><a href="#cb13-6" tabindex="-1"></a><span class="co">#> <chr> <int></span></span>
<span id="cb13-7"><a href="#cb13-7" tabindex="-1"></a><span class="co">#> 1 feminine 17</span></span>
<span id="cb13-8"><a href="#cb13-8" tabindex="-1"></a><span class="co">#> 2 masculine 66</span></span>
<span id="cb13-9"><a href="#cb13-9" tabindex="-1"></a><span class="co">#> 3 <NA> 4</span></span></code></pre></div>
</div>
</div>
<div id="verbs" class="section level2">
<h2>Verbs</h2>
<p>The following sections describe how grouping affects the main dplyr
verbs.</p>
<div id="summarise" class="section level3">
<h3><code>summarise()</code></h3>
<p><code>summarise()</code> computes a summary for each group. This
means that it starts from <code>group_keys()</code>, adding summary
variables to the right hand side:</p>
<div class="sourceCode" id="cb14"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb14-1"><a href="#cb14-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb14-2"><a href="#cb14-2" tabindex="-1"></a> <span class="fu">summarise</span>(</span>
<span id="cb14-3"><a href="#cb14-3" tabindex="-1"></a> <span class="at">n =</span> <span class="fu">n</span>(),</span>
<span id="cb14-4"><a href="#cb14-4" tabindex="-1"></a> <span class="at">height =</span> <span class="fu">mean</span>(height, <span class="at">na.rm =</span> <span class="cn">TRUE</span>)</span>
<span id="cb14-5"><a href="#cb14-5" tabindex="-1"></a> )</span>
<span id="cb14-6"><a href="#cb14-6" tabindex="-1"></a><span class="co">#> # A tibble: 38 × 3</span></span>
<span id="cb14-7"><a href="#cb14-7" tabindex="-1"></a><span class="co">#> species n height</span></span>
<span id="cb14-8"><a href="#cb14-8" tabindex="-1"></a><span class="co">#> <chr> <int> <dbl></span></span>
<span id="cb14-9"><a href="#cb14-9" tabindex="-1"></a><span class="co">#> 1 Aleena 1 79</span></span>
<span id="cb14-10"><a href="#cb14-10" tabindex="-1"></a><span class="co">#> 2 Besalisk 1 198</span></span>
<span id="cb14-11"><a href="#cb14-11" tabindex="-1"></a><span class="co">#> 3 Cerean 1 198</span></span>
<span id="cb14-12"><a href="#cb14-12" tabindex="-1"></a><span class="co">#> 4 Chagrian 1 196</span></span>
<span id="cb14-13"><a href="#cb14-13" tabindex="-1"></a><span class="co">#> # ℹ 34 more rows</span></span></code></pre></div>
<p>The <code>.groups=</code> argument controls the grouping structure of
the output. The historical behaviour of removing the right hand side
grouping variable corresponds to <code>.groups = "drop_last"</code>
without a message or <code>.groups = NULL</code> with a message (the
default).</p>
<div class="sourceCode" id="cb15"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb15-1"><a href="#cb15-1" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> </span>
<span id="cb15-2"><a href="#cb15-2" tabindex="-1"></a> <span class="fu">summarise</span>(<span class="at">n =</span> <span class="fu">n</span>()) <span class="sc">%>%</span> </span>
<span id="cb15-3"><a href="#cb15-3" tabindex="-1"></a> <span class="fu">group_vars</span>()</span>
<span id="cb15-4"><a href="#cb15-4" tabindex="-1"></a><span class="co">#> `summarise()` has grouped output by 'sex'. You can override using the `.groups`</span></span>
<span id="cb15-5"><a href="#cb15-5" tabindex="-1"></a><span class="co">#> argument.</span></span>
<span id="cb15-6"><a href="#cb15-6" tabindex="-1"></a><span class="co">#> [1] "sex"</span></span>
<span id="cb15-7"><a href="#cb15-7" tabindex="-1"></a></span>
<span id="cb15-8"><a href="#cb15-8" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> </span>
<span id="cb15-9"><a href="#cb15-9" tabindex="-1"></a> <span class="fu">summarise</span>(<span class="at">n =</span> <span class="fu">n</span>(), <span class="at">.groups =</span> <span class="st">"drop_last"</span>) <span class="sc">%>%</span> </span>
<span id="cb15-10"><a href="#cb15-10" tabindex="-1"></a> <span class="fu">group_vars</span>()</span>
<span id="cb15-11"><a href="#cb15-11" tabindex="-1"></a><span class="co">#> [1] "sex"</span></span></code></pre></div>
<p>Since version 1.0.0 the groups may also be kept
(<code>.groups = "keep"</code>) or dropped
(<code>.groups = "drop"</code>).</p>
<div class="sourceCode" id="cb16"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb16-1"><a href="#cb16-1" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> </span>
<span id="cb16-2"><a href="#cb16-2" tabindex="-1"></a> <span class="fu">summarise</span>(<span class="at">n =</span> <span class="fu">n</span>(), <span class="at">.groups =</span> <span class="st">"keep"</span>) <span class="sc">%>%</span> </span>
<span id="cb16-3"><a href="#cb16-3" tabindex="-1"></a> <span class="fu">group_vars</span>()</span>
<span id="cb16-4"><a href="#cb16-4" tabindex="-1"></a><span class="co">#> [1] "sex" "gender"</span></span>
<span id="cb16-5"><a href="#cb16-5" tabindex="-1"></a></span>
<span id="cb16-6"><a href="#cb16-6" tabindex="-1"></a>by_sex_gender <span class="sc">%>%</span> </span>
<span id="cb16-7"><a href="#cb16-7" tabindex="-1"></a> <span class="fu">summarise</span>(<span class="at">n =</span> <span class="fu">n</span>(), <span class="at">.groups =</span> <span class="st">"drop"</span>) <span class="sc">%>%</span> </span>
<span id="cb16-8"><a href="#cb16-8" tabindex="-1"></a> <span class="fu">group_vars</span>()</span>
<span id="cb16-9"><a href="#cb16-9" tabindex="-1"></a><span class="co">#> character(0)</span></span></code></pre></div>
<p>When the output no longer have grouping variables, it becomes
ungrouped (i.e. a regular tibble).</p>
</div>
<div id="select-rename-and-relocate" class="section level3">
<h3><code>select()</code>, <code>rename()</code>, and
<code>relocate()</code></h3>
<p><code>rename()</code> and <code>relocate()</code> behave identically
with grouped and ungrouped data because they only affect the name or
position of existing columns. Grouped <code>select()</code> is almost
identical to ungrouped select, except that it always includes the
grouping variables:</p>
<div class="sourceCode" id="cb17"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb17-1"><a href="#cb17-1" tabindex="-1"></a>by_species <span class="sc">%>%</span> <span class="fu">select</span>(mass)</span>
<span id="cb17-2"><a href="#cb17-2" tabindex="-1"></a><span class="co">#> Adding missing grouping variables: `species`</span></span>
<span id="cb17-3"><a href="#cb17-3" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 2</span></span>
<span id="cb17-4"><a href="#cb17-4" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb17-5"><a href="#cb17-5" tabindex="-1"></a><span class="co">#> species mass</span></span>
<span id="cb17-6"><a href="#cb17-6" tabindex="-1"></a><span class="co">#> <chr> <dbl></span></span>
<span id="cb17-7"><a href="#cb17-7" tabindex="-1"></a><span class="co">#> 1 Human 77</span></span>
<span id="cb17-8"><a href="#cb17-8" tabindex="-1"></a><span class="co">#> 2 Droid 75</span></span>
<span id="cb17-9"><a href="#cb17-9" tabindex="-1"></a><span class="co">#> 3 Droid 32</span></span>
<span id="cb17-10"><a href="#cb17-10" tabindex="-1"></a><span class="co">#> 4 Human 136</span></span>
<span id="cb17-11"><a href="#cb17-11" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span></code></pre></div>
<p>If you don’t want the grouping variables, you’ll have to first
<code>ungroup()</code>. (This design is possibly a mistake, but we’re
stuck with it for now.)</p>
</div>
<div id="arrange" class="section level3">
<h3><code>arrange()</code></h3>
<p>Grouped <code>arrange()</code> is the same as ungrouped
<code>arrange()</code>, unless you set <code>.by_group = TRUE</code>, in
which case it will order first by the grouping variables.</p>
<div class="sourceCode" id="cb18"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb18-1"><a href="#cb18-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb18-2"><a href="#cb18-2" tabindex="-1"></a> <span class="fu">arrange</span>(<span class="fu">desc</span>(mass)) <span class="sc">%>%</span></span>
<span id="cb18-3"><a href="#cb18-3" tabindex="-1"></a> <span class="fu">relocate</span>(species, mass)</span>
<span id="cb18-4"><a href="#cb18-4" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 14</span></span>
<span id="cb18-5"><a href="#cb18-5" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb18-6"><a href="#cb18-6" tabindex="-1"></a><span class="co">#> species mass name height hair_color skin_color eye_color birth_year sex </span></span>
<span id="cb18-7"><a href="#cb18-7" tabindex="-1"></a><span class="co">#> <chr> <dbl> <chr> <int> <chr> <chr> <chr> <dbl> <chr></span></span>
<span id="cb18-8"><a href="#cb18-8" tabindex="-1"></a><span class="co">#> 1 Hutt 1358 Jabba D… 175 <NA> green-tan… orange 600 herm…</span></span>
<span id="cb18-9"><a href="#cb18-9" tabindex="-1"></a><span class="co">#> 2 Kaleesh 159 Grievous 216 none brown, wh… green, y… NA male </span></span>
<span id="cb18-10"><a href="#cb18-10" tabindex="-1"></a><span class="co">#> 3 Droid 140 IG-88 200 none metal red 15 none </span></span>
<span id="cb18-11"><a href="#cb18-11" tabindex="-1"></a><span class="co">#> 4 Human 136 Darth V… 202 none white yellow 41.9 male </span></span>
<span id="cb18-12"><a href="#cb18-12" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span>
<span id="cb18-13"><a href="#cb18-13" tabindex="-1"></a><span class="co">#> # ℹ 5 more variables: gender <chr>, homeworld <chr>, films <list>,</span></span>
<span id="cb18-14"><a href="#cb18-14" tabindex="-1"></a><span class="co">#> # vehicles <list>, starships <list></span></span>
<span id="cb18-15"><a href="#cb18-15" tabindex="-1"></a></span>
<span id="cb18-16"><a href="#cb18-16" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb18-17"><a href="#cb18-17" tabindex="-1"></a> <span class="fu">arrange</span>(<span class="fu">desc</span>(mass), <span class="at">.by_group =</span> <span class="cn">TRUE</span>) <span class="sc">%>%</span></span>
<span id="cb18-18"><a href="#cb18-18" tabindex="-1"></a> <span class="fu">relocate</span>(species, mass)</span>
<span id="cb18-19"><a href="#cb18-19" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 14</span></span>
<span id="cb18-20"><a href="#cb18-20" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb18-21"><a href="#cb18-21" tabindex="-1"></a><span class="co">#> species mass name height hair_color skin_color eye_color birth_year sex </span></span>
<span id="cb18-22"><a href="#cb18-22" tabindex="-1"></a><span class="co">#> <chr> <dbl> <chr> <int> <chr> <chr> <chr> <dbl> <chr></span></span>
<span id="cb18-23"><a href="#cb18-23" tabindex="-1"></a><span class="co">#> 1 Aleena 15 Ratts … 79 none grey, blue unknown NA male </span></span>
<span id="cb18-24"><a href="#cb18-24" tabindex="-1"></a><span class="co">#> 2 Besalisk 102 Dexter… 198 none brown yellow NA male </span></span>
<span id="cb18-25"><a href="#cb18-25" tabindex="-1"></a><span class="co">#> 3 Cerean 82 Ki-Adi… 198 white pale yellow 92 male </span></span>
<span id="cb18-26"><a href="#cb18-26" tabindex="-1"></a><span class="co">#> 4 Chagrian NA Mas Am… 196 none blue blue NA male </span></span>
<span id="cb18-27"><a href="#cb18-27" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span>
<span id="cb18-28"><a href="#cb18-28" tabindex="-1"></a><span class="co">#> # ℹ 5 more variables: gender <chr>, homeworld <chr>, films <list>,</span></span>
<span id="cb18-29"><a href="#cb18-29" tabindex="-1"></a><span class="co">#> # vehicles <list>, starships <list></span></span></code></pre></div>
<p>Note that second example is sorted by <code>species</code> (from the
<code>group_by()</code> statement) and then by <code>mass</code> (within
species).</p>
</div>
<div id="mutate" class="section level3">
<h3><code>mutate()</code></h3>
<p>In simple cases with vectorised functions, grouped and ungrouped
<code>mutate()</code> give the same results. They differ when used with
summary functions:</p>
<div class="sourceCode" id="cb19"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb19-1"><a href="#cb19-1" tabindex="-1"></a><span class="co"># Subtract off global mean</span></span>
<span id="cb19-2"><a href="#cb19-2" tabindex="-1"></a>starwars <span class="sc">%>%</span> </span>
<span id="cb19-3"><a href="#cb19-3" tabindex="-1"></a> <span class="fu">select</span>(name, homeworld, mass) <span class="sc">%>%</span> </span>
<span id="cb19-4"><a href="#cb19-4" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">standard_mass =</span> mass <span class="sc">-</span> <span class="fu">mean</span>(mass, <span class="at">na.rm =</span> <span class="cn">TRUE</span>))</span>
<span id="cb19-5"><a href="#cb19-5" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 4</span></span>
<span id="cb19-6"><a href="#cb19-6" tabindex="-1"></a><span class="co">#> name homeworld mass standard_mass</span></span>
<span id="cb19-7"><a href="#cb19-7" tabindex="-1"></a><span class="co">#> <chr> <chr> <dbl> <dbl></span></span>
<span id="cb19-8"><a href="#cb19-8" tabindex="-1"></a><span class="co">#> 1 Luke Skywalker Tatooine 77 -20.3</span></span>
<span id="cb19-9"><a href="#cb19-9" tabindex="-1"></a><span class="co">#> 2 C-3PO Tatooine 75 -22.3</span></span>
<span id="cb19-10"><a href="#cb19-10" tabindex="-1"></a><span class="co">#> 3 R2-D2 Naboo 32 -65.3</span></span>
<span id="cb19-11"><a href="#cb19-11" tabindex="-1"></a><span class="co">#> 4 Darth Vader Tatooine 136 38.7</span></span>
<span id="cb19-12"><a href="#cb19-12" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span>
<span id="cb19-13"><a href="#cb19-13" tabindex="-1"></a></span>
<span id="cb19-14"><a href="#cb19-14" tabindex="-1"></a><span class="co"># Subtract off homeworld mean</span></span>
<span id="cb19-15"><a href="#cb19-15" tabindex="-1"></a>starwars <span class="sc">%>%</span> </span>
<span id="cb19-16"><a href="#cb19-16" tabindex="-1"></a> <span class="fu">select</span>(name, homeworld, mass) <span class="sc">%>%</span> </span>
<span id="cb19-17"><a href="#cb19-17" tabindex="-1"></a> <span class="fu">group_by</span>(homeworld) <span class="sc">%>%</span> </span>
<span id="cb19-18"><a href="#cb19-18" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">standard_mass =</span> mass <span class="sc">-</span> <span class="fu">mean</span>(mass, <span class="at">na.rm =</span> <span class="cn">TRUE</span>))</span>
<span id="cb19-19"><a href="#cb19-19" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 4</span></span>
<span id="cb19-20"><a href="#cb19-20" tabindex="-1"></a><span class="co">#> # Groups: homeworld [49]</span></span>
<span id="cb19-21"><a href="#cb19-21" tabindex="-1"></a><span class="co">#> name homeworld mass standard_mass</span></span>
<span id="cb19-22"><a href="#cb19-22" tabindex="-1"></a><span class="co">#> <chr> <chr> <dbl> <dbl></span></span>
<span id="cb19-23"><a href="#cb19-23" tabindex="-1"></a><span class="co">#> 1 Luke Skywalker Tatooine 77 -8.38</span></span>
<span id="cb19-24"><a href="#cb19-24" tabindex="-1"></a><span class="co">#> 2 C-3PO Tatooine 75 -10.4 </span></span>
<span id="cb19-25"><a href="#cb19-25" tabindex="-1"></a><span class="co">#> 3 R2-D2 Naboo 32 -32.2 </span></span>
<span id="cb19-26"><a href="#cb19-26" tabindex="-1"></a><span class="co">#> 4 Darth Vader Tatooine 136 50.6 </span></span>
<span id="cb19-27"><a href="#cb19-27" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span></code></pre></div>
<p>Or with window functions like <code>min_rank()</code>:</p>
<div class="sourceCode" id="cb20"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb20-1"><a href="#cb20-1" tabindex="-1"></a><span class="co"># Overall rank</span></span>
<span id="cb20-2"><a href="#cb20-2" tabindex="-1"></a>starwars <span class="sc">%>%</span> </span>
<span id="cb20-3"><a href="#cb20-3" tabindex="-1"></a> <span class="fu">select</span>(name, homeworld, height) <span class="sc">%>%</span> </span>
<span id="cb20-4"><a href="#cb20-4" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">rank =</span> <span class="fu">min_rank</span>(height))</span>
<span id="cb20-5"><a href="#cb20-5" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 4</span></span>
<span id="cb20-6"><a href="#cb20-6" tabindex="-1"></a><span class="co">#> name homeworld height rank</span></span>
<span id="cb20-7"><a href="#cb20-7" tabindex="-1"></a><span class="co">#> <chr> <chr> <int> <int></span></span>
<span id="cb20-8"><a href="#cb20-8" tabindex="-1"></a><span class="co">#> 1 Luke Skywalker Tatooine 172 28</span></span>
<span id="cb20-9"><a href="#cb20-9" tabindex="-1"></a><span class="co">#> 2 C-3PO Tatooine 167 20</span></span>
<span id="cb20-10"><a href="#cb20-10" tabindex="-1"></a><span class="co">#> 3 R2-D2 Naboo 96 5</span></span>
<span id="cb20-11"><a href="#cb20-11" tabindex="-1"></a><span class="co">#> 4 Darth Vader Tatooine 202 72</span></span>
<span id="cb20-12"><a href="#cb20-12" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span>
<span id="cb20-13"><a href="#cb20-13" tabindex="-1"></a></span>
<span id="cb20-14"><a href="#cb20-14" tabindex="-1"></a><span class="co"># Rank per homeworld</span></span>
<span id="cb20-15"><a href="#cb20-15" tabindex="-1"></a>starwars <span class="sc">%>%</span> </span>
<span id="cb20-16"><a href="#cb20-16" tabindex="-1"></a> <span class="fu">select</span>(name, homeworld, height) <span class="sc">%>%</span> </span>
<span id="cb20-17"><a href="#cb20-17" tabindex="-1"></a> <span class="fu">group_by</span>(homeworld) <span class="sc">%>%</span> </span>
<span id="cb20-18"><a href="#cb20-18" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">rank =</span> <span class="fu">min_rank</span>(height))</span>
<span id="cb20-19"><a href="#cb20-19" tabindex="-1"></a><span class="co">#> # A tibble: 87 × 4</span></span>
<span id="cb20-20"><a href="#cb20-20" tabindex="-1"></a><span class="co">#> # Groups: homeworld [49]</span></span>
<span id="cb20-21"><a href="#cb20-21" tabindex="-1"></a><span class="co">#> name homeworld height rank</span></span>
<span id="cb20-22"><a href="#cb20-22" tabindex="-1"></a><span class="co">#> <chr> <chr> <int> <int></span></span>
<span id="cb20-23"><a href="#cb20-23" tabindex="-1"></a><span class="co">#> 1 Luke Skywalker Tatooine 172 5</span></span>
<span id="cb20-24"><a href="#cb20-24" tabindex="-1"></a><span class="co">#> 2 C-3PO Tatooine 167 4</span></span>
<span id="cb20-25"><a href="#cb20-25" tabindex="-1"></a><span class="co">#> 3 R2-D2 Naboo 96 1</span></span>
<span id="cb20-26"><a href="#cb20-26" tabindex="-1"></a><span class="co">#> 4 Darth Vader Tatooine 202 10</span></span>
<span id="cb20-27"><a href="#cb20-27" tabindex="-1"></a><span class="co">#> # ℹ 83 more rows</span></span></code></pre></div>
</div>
<div id="filter" class="section level3">
<h3><code>filter()</code></h3>
<p>A grouped <code>filter()</code> effectively does a
<code>mutate()</code> to generate a logical variable, and then only
keeps the rows where the variable is <code>TRUE</code>. This means that
grouped filters can be used with summary functions. For example, we can
find the tallest character of each species:</p>
<div class="sourceCode" id="cb21"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb21-1"><a href="#cb21-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb21-2"><a href="#cb21-2" tabindex="-1"></a> <span class="fu">select</span>(name, species, height) <span class="sc">%>%</span> </span>
<span id="cb21-3"><a href="#cb21-3" tabindex="-1"></a> <span class="fu">filter</span>(height <span class="sc">==</span> <span class="fu">max</span>(height))</span>
<span id="cb21-4"><a href="#cb21-4" tabindex="-1"></a><span class="co">#> # A tibble: 36 × 3</span></span>
<span id="cb21-5"><a href="#cb21-5" tabindex="-1"></a><span class="co">#> # Groups: species [36]</span></span>
<span id="cb21-6"><a href="#cb21-6" tabindex="-1"></a><span class="co">#> name species height</span></span>
<span id="cb21-7"><a href="#cb21-7" tabindex="-1"></a><span class="co">#> <chr> <chr> <int></span></span>
<span id="cb21-8"><a href="#cb21-8" tabindex="-1"></a><span class="co">#> 1 Greedo Rodian 173</span></span>
<span id="cb21-9"><a href="#cb21-9" tabindex="-1"></a><span class="co">#> 2 Jabba Desilijic Tiure Hutt 175</span></span>
<span id="cb21-10"><a href="#cb21-10" tabindex="-1"></a><span class="co">#> 3 Yoda Yoda's species 66</span></span>
<span id="cb21-11"><a href="#cb21-11" tabindex="-1"></a><span class="co">#> 4 Bossk Trandoshan 190</span></span>
<span id="cb21-12"><a href="#cb21-12" tabindex="-1"></a><span class="co">#> # ℹ 32 more rows</span></span></code></pre></div>
<p>You can also use <code>filter()</code> to remove entire groups. For
example, the following code eliminates all groups that only have a
single member:</p>
<div class="sourceCode" id="cb22"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb22-1"><a href="#cb22-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb22-2"><a href="#cb22-2" tabindex="-1"></a> <span class="fu">filter</span>(<span class="fu">n</span>() <span class="sc">!=</span> <span class="dv">1</span>) <span class="sc">%>%</span> </span>
<span id="cb22-3"><a href="#cb22-3" tabindex="-1"></a> <span class="fu">tally</span>()</span>
<span id="cb22-4"><a href="#cb22-4" tabindex="-1"></a><span class="co">#> # A tibble: 9 × 2</span></span>
<span id="cb22-5"><a href="#cb22-5" tabindex="-1"></a><span class="co">#> species n</span></span>
<span id="cb22-6"><a href="#cb22-6" tabindex="-1"></a><span class="co">#> <chr> <int></span></span>
<span id="cb22-7"><a href="#cb22-7" tabindex="-1"></a><span class="co">#> 1 Droid 6</span></span>
<span id="cb22-8"><a href="#cb22-8" tabindex="-1"></a><span class="co">#> 2 Gungan 3</span></span>
<span id="cb22-9"><a href="#cb22-9" tabindex="-1"></a><span class="co">#> 3 Human 35</span></span>
<span id="cb22-10"><a href="#cb22-10" tabindex="-1"></a><span class="co">#> 4 Kaminoan 2</span></span>
<span id="cb22-11"><a href="#cb22-11" tabindex="-1"></a><span class="co">#> # ℹ 5 more rows</span></span></code></pre></div>
</div>
<div id="slice-and-friends" class="section level3">
<h3><code>slice()</code> and friends</h3>
<p><code>slice()</code> and friends (<code>slice_head()</code>,
<code>slice_tail()</code>, <code>slice_sample()</code>,
<code>slice_min()</code> and <code>slice_max()</code>) select rows
within a group. For example, we can select the first observation within
each species:</p>
<div class="sourceCode" id="cb23"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb23-1"><a href="#cb23-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb23-2"><a href="#cb23-2" tabindex="-1"></a> <span class="fu">relocate</span>(species) <span class="sc">%>%</span> </span>
<span id="cb23-3"><a href="#cb23-3" tabindex="-1"></a> <span class="fu">slice</span>(<span class="dv">1</span>)</span>
<span id="cb23-4"><a href="#cb23-4" tabindex="-1"></a><span class="co">#> # A tibble: 38 × 14</span></span>
<span id="cb23-5"><a href="#cb23-5" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb23-6"><a href="#cb23-6" tabindex="-1"></a><span class="co">#> species name height mass hair_color skin_color eye_color birth_year sex </span></span>
<span id="cb23-7"><a href="#cb23-7" tabindex="-1"></a><span class="co">#> <chr> <chr> <int> <dbl> <chr> <chr> <chr> <dbl> <chr></span></span>
<span id="cb23-8"><a href="#cb23-8" tabindex="-1"></a><span class="co">#> 1 Aleena Ratts … 79 15 none grey, blue unknown NA male </span></span>
<span id="cb23-9"><a href="#cb23-9" tabindex="-1"></a><span class="co">#> 2 Besalisk Dexter… 198 102 none brown yellow NA male </span></span>
<span id="cb23-10"><a href="#cb23-10" tabindex="-1"></a><span class="co">#> 3 Cerean Ki-Adi… 198 82 white pale yellow 92 male </span></span>
<span id="cb23-11"><a href="#cb23-11" tabindex="-1"></a><span class="co">#> 4 Chagrian Mas Am… 196 NA none blue blue NA male </span></span>
<span id="cb23-12"><a href="#cb23-12" tabindex="-1"></a><span class="co">#> # ℹ 34 more rows</span></span>
<span id="cb23-13"><a href="#cb23-13" tabindex="-1"></a><span class="co">#> # ℹ 5 more variables: gender <chr>, homeworld <chr>, films <list>,</span></span>
<span id="cb23-14"><a href="#cb23-14" tabindex="-1"></a><span class="co">#> # vehicles <list>, starships <list></span></span></code></pre></div>
<p>Similarly, we can use <code>slice_min()</code> to select the smallest
<code>n</code> values of a variable:</p>
<div class="sourceCode" id="cb24"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb24-1"><a href="#cb24-1" tabindex="-1"></a>by_species <span class="sc">%>%</span></span>
<span id="cb24-2"><a href="#cb24-2" tabindex="-1"></a> <span class="fu">filter</span>(<span class="sc">!</span><span class="fu">is.na</span>(height)) <span class="sc">%>%</span> </span>
<span id="cb24-3"><a href="#cb24-3" tabindex="-1"></a> <span class="fu">slice_min</span>(height, <span class="at">n =</span> <span class="dv">2</span>)</span>
<span id="cb24-4"><a href="#cb24-4" tabindex="-1"></a><span class="co">#> # A tibble: 47 × 14</span></span>
<span id="cb24-5"><a href="#cb24-5" tabindex="-1"></a><span class="co">#> # Groups: species [38]</span></span>
<span id="cb24-6"><a href="#cb24-6" tabindex="-1"></a><span class="co">#> name height mass hair_color skin_color eye_color birth_year sex gender</span></span>
<span id="cb24-7"><a href="#cb24-7" tabindex="-1"></a><span class="co">#> <chr> <int> <dbl> <chr> <chr> <chr> <dbl> <chr> <chr> </span></span>
<span id="cb24-8"><a href="#cb24-8" tabindex="-1"></a><span class="co">#> 1 Ratts Ty… 79 15 none grey, blue unknown NA male mascu…</span></span>
<span id="cb24-9"><a href="#cb24-9" tabindex="-1"></a><span class="co">#> 2 Dexter J… 198 102 none brown yellow NA male mascu…</span></span>
<span id="cb24-10"><a href="#cb24-10" tabindex="-1"></a><span class="co">#> 3 Ki-Adi-M… 198 82 white pale yellow 92 male mascu…</span></span>
<span id="cb24-11"><a href="#cb24-11" tabindex="-1"></a><span class="co">#> 4 Mas Amed… 196 NA none blue blue NA male mascu…</span></span>
<span id="cb24-12"><a href="#cb24-12" tabindex="-1"></a><span class="co">#> # ℹ 43 more rows</span></span>
<span id="cb24-13"><a href="#cb24-13" tabindex="-1"></a><span class="co">#> # ℹ 5 more variables: homeworld <chr>, species <chr>, films <list>,</span></span>
<span id="cb24-14"><a href="#cb24-14" tabindex="-1"></a><span class="co">#> # vehicles <list>, starships <list></span></span></code></pre></div>
</div>
</div>
<div class="footnotes footnotes-end-of-document">
<hr />
<ol>
<li id="fn1"><p>Note that the argument changed from
<code>add = TRUE</code> to <code>.add = TRUE</code> in dplyr 1.0.0.<a href="#fnref1" class="footnote-back">↩︎</a></p></li>
</ol>
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