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<!DOCTYPE html>
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<title>Cheatsheet for dplyr join functions</title>
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<h1 class="title toc-ignore">Cheatsheet for dplyr join functions</h1>
<h4 class="author"><em>Jenny Bryan</em></h4>
</div>
<div id="TOC">
<ul>
<li><a href="#why-the-cheatsheet">Why the cheatsheet</a></li>
<li><a href="#inner_joinsuperheroes-publishers">inner_join(superheroes, publishers)</a></li>
<li><a href="#semi_joinsuperheroes-publishers">semi_join(superheroes, publishers)</a></li>
<li><a href="#left_joinsuperheroes-publishers">left_join(superheroes, publishers)</a></li>
<li><a href="#anti_joinsuperheroes-publishers">anti_join(superheroes, publishers)</a></li>
<li><a href="#inner_joinpublishers-superheroes">inner_join(publishers, superheroes)</a></li>
<li><a href="#semi_joinpublishers-superheroes">semi_join(publishers, superheroes)</a></li>
<li><a href="#left_joinpublishers-superheroes">left_join(publishers, superheroes)</a></li>
<li><a href="#anti_joinpublishers-superheroes">anti_join(publishers, superheroes)</a></li>
<li><a href="#full_joinsuperheroes-publishers">full_join(superheroes, publishers)</a></li>
<li><a href="#sessioninfo">sessionInfo()</a></li>
</ul>
</div>
<div id="why-the-cheatsheet" class="section level4">
<h4>Why the cheatsheet</h4>
<p>Examples for those of us who don’t speak SQL so good. There are lots of <a href="//encrypted.google.com/search?q=sql+join&tbm=isch">Venn diagrams re: SQL joins on the interwebs</a>, but I wanted R examples.</p>
<p><a href="http://www.rdocumentation.org/packages/dplyr">Full documentation</a> for the dplyr package, which is developed by Hadley Wickham and Romain Francois on <a href="https://github.com/hadley/dplyr">GitHub</a>. The <a href="https://cran.r-project.org/web/packages/dplyr/vignettes/two-table.html">vignette on Two-table verbs</a> covers the joins shown here.</p>
<p>Working with two small data.frames, <code>superheroes</code> and <code>publishers</code>.</p>
<pre class="r"><code>suppressPackageStartupMessages(library(dplyr))
library(readr)
superheroes <- "
name, alignment, gender, publisher
Magneto, bad, male, Marvel
Storm, good, female, Marvel
Mystique, bad, female, Marvel
Batman, good, male, DC
Joker, bad, male, DC
Catwoman, bad, female, DC
Hellboy, good, male, Dark Horse Comics
"
superheroes <- read_csv(superheroes, trim_ws = TRUE, skip = 1)
publishers <- "
publisher, yr_founded
DC, 1934
Marvel, 1939
Image, 1992
"
publishers <- read_csv(publishers, trim_ws = TRUE, skip = 1)</code></pre>
<p>Sorry, cheat sheet does not illustrate “multiple match” situations terribly well.</p>
<p>Sub-plot: watch the row and variable order of the join results for a healthy reminder of why it’s dangerous to rely on any of that in an analysis.</p>
</div>
<div id="inner_joinsuperheroes-publishers" class="section level4">
<h4>inner_join(superheroes, publishers)</h4>
<blockquote>
<p>inner_join(x, y): Return all rows from x where there are matching values in y, and all columns from x and y. If there are multiple matches between x and y, all combination of the matches are returned. This is a mutating join.</p>
</blockquote>
<pre class="r"><code>(ijsp <- inner_join(superheroes, publishers))
#> Joining, by = "publisher"
#> # A tibble: 6 × 5
#> name alignment gender publisher yr_founded
#> <chr> <chr> <chr> <chr> <int>
#> 1 Magneto bad male Marvel 1939
#> 2 Storm good female Marvel 1939
#> 3 Mystique bad female Marvel 1939
#> 4 Batman good male DC 1934
#> 5 Joker bad male DC 1934
#> 6 Catwoman bad female DC 1934</code></pre>
<p>We lose Hellboy in the join because, although he appears in <code>x = superheroes</code>, his publisher Dark Horse Comics does not appear in <code>y = publishers</code>. The join result has all variables from <code>x = superheroes</code> plus <code>yr_founded</code>, from <code>y</code>.</p>
<table border="1">
<tr>
<td valign="top">
<p>superheroes</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>publishers</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Image</td>
<td align="right">1992</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>inner_join(x = superheroes, y = publishers)</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
<div id="semi_joinsuperheroes-publishers" class="section level4">
<h4>semi_join(superheroes, publishers)</h4>
<blockquote>
<p>semi_join(x, y): Return all rows from x where there are matching values in y, keeping just columns from x. A semi join differs from an inner join because an inner join will return one row of x for each matching row of y, where a semi join will never duplicate rows of x. This is a filtering join.</p>
</blockquote>
<pre class="r"><code>(sjsp <- semi_join(superheroes, publishers))
#> Joining, by = "publisher"
#> # A tibble: 6 × 4
#> name alignment gender publisher
#> <chr> <chr> <chr> <chr>
#> 1 Batman good male DC
#> 2 Joker bad male DC
#> 3 Catwoman bad female DC
#> 4 Magneto bad male Marvel
#> 5 Storm good female Marvel
#> 6 Mystique bad female Marvel</code></pre>
<p>We get a similar result as with <code>inner_join()</code> but the join result contains only the variables originally found in <code>x = superheroes</code>. But note the row order has changed.</p>
<table border="1">
<tr>
<td valign="top">
<p>superheroes</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>publishers</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Image</td>
<td align="right">1992</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>semi-join(x = superheroes, y = publishers)</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
</tr>
<tr class="odd">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
<div id="left_joinsuperheroes-publishers" class="section level4">
<h4>left_join(superheroes, publishers)</h4>
<blockquote>
<p>left_join(x, y): Return all rows from x, and all columns from x and y. If there are multiple matches between x and y, all combination of the matches are returned. This is a mutating join.</p>
</blockquote>
<pre class="r"><code>(ljsp <- left_join(superheroes, publishers))
#> Joining, by = "publisher"
#> # A tibble: 7 × 5
#> name alignment gender publisher yr_founded
#> <chr> <chr> <chr> <chr> <int>
#> 1 Magneto bad male Marvel 1939
#> 2 Storm good female Marvel 1939
#> 3 Mystique bad female Marvel 1939
#> 4 Batman good male DC 1934
#> 5 Joker bad male DC 1934
#> 6 Catwoman bad female DC 1934
#> 7 Hellboy good male Dark Horse Comics NA</code></pre>
<p>We basically get <code>x = superheroes</code> back, but with the addition of variable <code>yr_founded</code>, which is unique to <code>y = publishers</code>. Hellboy, whose publisher does not appear in <code>y = publishers</code>, has an <code>NA</code> for <code>yr_founded</code>.</p>
<table border="1">
<tr>
<td valign="top">
<p>superheroes</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>publishers</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Image</td>
<td align="right">1992</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>left_join(x = superheroes, y = publishers)</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
<td align="right">NA</td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
<div id="anti_joinsuperheroes-publishers" class="section level4">
<h4>anti_join(superheroes, publishers)</h4>
<blockquote>
<p>anti_join(x, y): Return all rows from x where there are not matching values in y, keeping just columns from x. This is a filtering join.</p>
</blockquote>
<pre class="r"><code>(ajsp <- anti_join(superheroes, publishers))
#> Joining, by = "publisher"
#> # A tibble: 1 × 4
#> name alignment gender publisher
#> <chr> <chr> <chr> <chr>
#> 1 Hellboy good male Dark Horse Comics</code></pre>
<p>We keep <strong>only</strong> Hellboy now (and do not get <code>yr_founded</code>).</p>
<table border="1">
<tr>
<td valign="top">
<p>superheroes</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>publishers</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Image</td>
<td align="right">1992</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>anti_join(x = superheroes, y = publishers)</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
<div id="inner_joinpublishers-superheroes" class="section level4">
<h4>inner_join(publishers, superheroes)</h4>
<blockquote>
<p>inner_join(x, y): Return all rows from x where there are matching values in y, and all columns from x and y. If there are multiple matches between x and y, all combination of the matches are returned. This is a mutating join.</p>
</blockquote>
<pre class="r"><code>(ijps <- inner_join(publishers, superheroes))
#> Joining, by = "publisher"
#> # A tibble: 6 × 5
#> publisher yr_founded name alignment gender
#> <chr> <int> <chr> <chr> <chr>
#> 1 DC 1934 Batman good male
#> 2 DC 1934 Joker bad male
#> 3 DC 1934 Catwoman bad female
#> 4 Marvel 1939 Magneto bad male
#> 5 Marvel 1939 Storm good female
#> 6 Marvel 1939 Mystique bad female</code></pre>
<p>In a way, this does illustrate multiple matches, if you think about it from the <code>x = publishers</code> direction. Every publisher that has a match in <code>y = superheroes</code> appears multiple times in the result, once for each match. In fact, we’re getting the same result as with <code>inner_join(superheroes, publishers)</code>, up to variable order (which you should also never rely on in an analysis).</p>
<table border="1">
<tr>
<td valign="top">
<p>publishers</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>
<tr class="odd">
<td align="left">Image</td>
<td align="right">1992</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>superheroes</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
<th align="left">publisher</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="odd">
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">Marvel</td>
</tr>
<tr class="even">
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
<td align="left">DC</td>
</tr>
<tr class="even">
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
<td align="left">DC</td>
</tr>
<tr class="odd">
<td align="left">Hellboy</td>
<td align="left">good</td>
<td align="left">male</td>
<td align="left">Dark Horse Comics</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<p>inner_join(x = publishers, y = superheroes)</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
<th align="left">name</th>
<th align="left">alignment</th>
<th align="left">gender</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
<td align="left">Batman</td>
<td align="left">good</td>
<td align="left">male</td>
</tr>
<tr class="even">
<td align="left">DC</td>
<td align="right">1934</td>
<td align="left">Joker</td>
<td align="left">bad</td>
<td align="left">male</td>
</tr>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
<td align="left">Catwoman</td>
<td align="left">bad</td>
<td align="left">female</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
<td align="left">Magneto</td>
<td align="left">bad</td>
<td align="left">male</td>
</tr>
<tr class="odd">
<td align="left">Marvel</td>
<td align="right">1939</td>
<td align="left">Storm</td>
<td align="left">good</td>
<td align="left">female</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
<td align="left">Mystique</td>
<td align="left">bad</td>
<td align="left">female</td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
<div id="semi_joinpublishers-superheroes" class="section level4">
<h4>semi_join(publishers, superheroes)</h4>
<blockquote>
<p>semi_join(x, y): Return all rows from x where there are matching values in y, keeping just columns from x. A semi join differs from an inner join because an inner join will return one row of x for each matching row of y, where a semi join will never duplicate rows of x. This is a filtering join.</p>
</blockquote>
<pre class="r"><code>(sjps <- semi_join(x = publishers, y = superheroes))
#> Joining, by = "publisher"
#> # A tibble: 2 × 2
#> publisher yr_founded
#> <chr> <int>
#> 1 Marvel 1939
#> 2 DC 1934</code></pre>
<p>Now the effects of switching the <code>x</code> and <code>y</code> roles is more clear. The result resembles <code>x = publishers</code>, but the publisher Image is lost, because there are no observations where <code>publisher == "Image"</code> in <code>y = superheroes</code>.</p>
<table border="1">
<tr>
<td valign="top">
<p>publishers</p>
<table>
<thead>
<tr class="header">
<th align="left">publisher</th>
<th align="right">yr_founded</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">DC</td>
<td align="right">1934</td>
</tr>
<tr class="even">
<td align="left">Marvel</td>
<td align="right">1939</td>
</tr>