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<div id="header">
<h1 class="title toc-ignore">Data Wrangling at Scale with data.table</h1>
</div>
<p>This presentation will detail data.tables data wrangling functionality, including:</p>
<ul>
<li>Manipulating data</li>
<li>Modifying variables</li>
<li>Summarizing data</li>
<li>Chaining</li>
<li>Joining</li>
<li>Plotting data</li>
</ul>
<p>We will end the presentation with an exercise.</p>
<div id="whats-data-wrangling" class="section level1">
<h1>What’s data wrangling? 🤔</h1>
<p>Data wrangling is the process of converting raw data to another format which can be readily analyzable.</p>
<p><img src="pics/data_wrangling.png" width="40%" style="display: block; margin: auto;" /></p>
</div>
<div id="data.table" class="section level1">
<h1>data.table 📹</h1>
<p><code>data.table</code> provides an efficient and high performance alternative of base R’s data.frame when conducting data wrangling.</p>
<p><code>data.table</code> enables this efficiency by providing:</p>
<ul>
<li>concise syntax: fast to type, fast to read</li>
<li>fast speed</li>
<li>memory efficiency</li>
<li>a large community</li>
<li>rich features</li>
</ul>
<p>To install the package, we use <code>install.packages('data.table')</code>.</p>
<div id="importing-with-fread" class="section level2">
<h2>Importing with <code>fread()</code></h2>
<p><code>data.table</code>’s efficiency begins from the outset with <code>fread()</code>, which is short for fast read is data.table’s version of <code>read_csv()</code>.</p>
<p>Let’s import and read the <code>mtcars</code> dataset and call it <code>mt</code> using <code>fread()</code>.</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">library</span>(data.table)</span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a>mt <span class="ot"><-</span> <span class="fu">fread</span>(<span class="st">"mtcars.csv"</span>)</span></code></pre></div>
<p>Let’s check how fast <code>fread()</code> actually is it compared to <code>read.csv</code>. You can also write a file using <code>fwrite()</code> in <code>data.table</code> like <code>write.csv</code>.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Create a large .csv file</span></span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="fu">set.seed</span>(<span class="dv">28</span>)</span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a>trial <span class="ot"><-</span> <span class="fu">data.frame</span>(<span class="fu">matrix</span>(<span class="fu">runif</span>(<span class="dv">10000000</span>), <span class="at">nrow=</span><span class="dv">1000000</span>))</span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="co">#write.csv(trial, 'trial.csv', row.names = F)</span></span></code></pre></div>
<p>We can then see that <code>fread()</code> is at least 20 times faster! Let’s check it out!</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Time taken by read.csv to import</span></span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a><span class="fu">system.time</span>({trial_df <span class="ot"><-</span> <span class="fu">read.csv</span>(<span class="st">'trial.csv'</span>)})</span></code></pre></div>
<pre><code>## user system elapsed
## 38.69 0.64 39.45</code></pre>
<div class="sourceCode" id="cb5"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Time taken by fread to import</span></span>
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a><span class="fu">system.time</span>({trial_df <span class="ot"><-</span> <span class="fu">fread</span>(<span class="st">'trial.csv'</span>)})</span></code></pre></div>
<pre><code>## user system elapsed
## 0.42 0.13 0.14</code></pre>
</div>
<div id="creating-data-tables" class="section level2">
<h2>Creating data tables</h2>
<p>To highlight what a data table is, we will create data tables using different functions and compare the results with a data frame. Let’s use a built-in R data called <code>airquality</code>.</p>
<div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span>(airquality)</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="right">Ozone</th>
<th align="right">Solar.R</th>
<th align="right">Wind</th>
<th align="right">Temp</th>
<th align="right">Month</th>
<th align="right">Day</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="right">41</td>
<td align="right">190</td>
<td align="right">7.4</td>
<td align="right">67</td>
<td align="right">5</td>
<td align="right">1</td>
</tr>
<tr class="even">
<td align="right">36</td>
<td align="right">118</td>
<td align="right">8.0</td>
<td align="right">72</td>
<td align="right">5</td>
<td align="right">2</td>
</tr>
<tr class="odd">
<td align="right">12</td>
<td align="right">149</td>
<td align="right">12.6</td>
<td align="right">74</td>
<td align="right">5</td>
<td align="right">3</td>
</tr>
<tr class="even">
<td align="right">18</td>
<td align="right">313</td>
<td align="right">11.5</td>
<td align="right">62</td>
<td align="right">5</td>
<td align="right">4</td>
</tr>
<tr class="odd">
<td align="right">NA</td>
<td align="right">NA</td>
<td align="right">14.3</td>
<td align="right">56</td>
<td align="right">5</td>
<td align="right">5</td>
</tr>
<tr class="even">
<td align="right">28</td>
<td align="right">NA</td>
<td align="right">14.9</td>
<td align="right">66</td>
<td align="right">5</td>
<td align="right">6</td>
</tr>
</tbody>
</table>
</div>
<div class="sourceCode" id="cb8"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a><span class="fu">class</span>(airquality)</span></code></pre></div>
<pre><code>## [1] "data.frame"</code></pre>
<p>To convert this data frame to a data table, we can either use:</p>
<ul>
<li><p><code>data.table()</code> and <code>as.data.table()</code> - This function creates a copy of the data and converts it to a data.table</p></li>
<li><p><code>setDT()</code> - This function converts the data to a data.table, there is then no need to assign to a new object</p></li>
</ul>
<p>We convert <code>airquality</code> data frame to a data table using <code>as.data.table</code>. It then becomes both a data table and a data frame.</p>
<div class="sourceCode" id="cb10"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="fu">class</span>(airquality)</span></code></pre></div>
<pre><code>## [1] "data.frame"</code></pre>
<div class="sourceCode" id="cb12"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb12-1"><a href="#cb12-1" aria-hidden="true" tabindex="-1"></a>airqualityDT <span class="ot"><-</span> <span class="fu">as.data.table</span>(airquality)</span>
<span id="cb12-2"><a href="#cb12-2" aria-hidden="true" tabindex="-1"></a><span class="fu">class</span>(airqualityDT)</span></code></pre></div>
<pre><code>## [1] "data.table" "data.frame"</code></pre>
<p>Now, we do the same for the <code>mt</code> data frame.</p>
<div class="sourceCode" id="cb14"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a>mt <span class="ot"><-</span> <span class="fu">as.data.frame</span>(<span class="fu">fread</span>(<span class="st">"mtcars.csv"</span>))</span>
<span id="cb14-2"><a href="#cb14-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb14-3"><a href="#cb14-3" aria-hidden="true" tabindex="-1"></a><span class="fu">class</span>(mt)</span></code></pre></div>
<pre><code>## [1] "data.frame"</code></pre>
<div class="sourceCode" id="cb16"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><span class="fu">setDT</span>(mt) <span class="co"># we do not need to assign mt to a new object</span></span>
<span id="cb16-2"><a href="#cb16-2" aria-hidden="true" tabindex="-1"></a><span class="fu">class</span>(mt)</span></code></pre></div>
<pre><code>## [1] "data.table" "data.frame"</code></pre>
<div class="sourceCode" id="cb18"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a><span class="co"># for illustration purposes, let's use `as.data.table` and assign it to mtDT</span></span>
<span id="cb18-2"><a href="#cb18-2" aria-hidden="true" tabindex="-1"></a>mtDT <span class="ot"><-</span> <span class="fu">as.data.table</span>(mt)</span>
<span id="cb18-3"><a href="#cb18-3" aria-hidden="true" tabindex="-1"></a><span class="fu">class</span>(mtDT)</span></code></pre></div>
<pre><code>## [1] "data.table" "data.frame"</code></pre>
<p>We can “manually” create a data table using <code>data.table()</code>.</p>
<div class="sourceCode" id="cb20"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a>DT <span class="ot"><-</span> <span class="fu">data.table</span>(<span class="at">x =</span> <span class="dv">1</span><span class="sc">:</span><span class="dv">8</span>,</span>
<span id="cb20-2"><a href="#cb20-2" aria-hidden="true" tabindex="-1"></a> <span class="at">y =</span> <span class="fu">round</span>(pi<span class="sc">*</span><span class="dv">1</span><span class="sc">:</span><span class="dv">8</span>,<span class="dv">2</span>),</span>
<span id="cb20-3"><a href="#cb20-3" aria-hidden="true" tabindex="-1"></a> <span class="at">z =</span> letters[<span class="dv">1</span><span class="sc">:</span><span class="dv">8</span>])</span>
<span id="cb20-4"><a href="#cb20-4" aria-hidden="true" tabindex="-1"></a>knitr<span class="sc">::</span><span class="fu">kable</span>(DT)</span></code></pre></div>
<table>
<thead>
<tr class="header">
<th align="right">x</th>
<th align="right">y</th>
<th align="left">z</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="right">1</td>
<td align="right">3.14</td>
<td align="left">a</td>
</tr>
<tr class="even">
<td align="right">2</td>
<td align="right">6.28</td>
<td align="left">b</td>
</tr>
<tr class="odd">
<td align="right">3</td>
<td align="right">9.42</td>
<td align="left">c</td>
</tr>
<tr class="even">
<td align="right">4</td>
<td align="right">12.57</td>
<td align="left">d</td>
</tr>
<tr class="odd">
<td align="right">5</td>
<td align="right">15.71</td>
<td align="left">e</td>
</tr>
<tr class="even">
<td align="right">6</td>
<td align="right">18.85</td>
<td align="left">f</td>
</tr>
<tr class="odd">
<td align="right">7</td>
<td align="right">21.99</td>
<td align="left">g</td>
</tr>
<tr class="even">
<td align="right">8</td>
<td align="right">25.13</td>
<td align="left">h</td>
</tr>
</tbody>
</table>
<p>Packages and functions that work with data frames also work for data tables. Since a data.table is a data.frame, it is compatible with R functions and packages that accept only data.frames.</p>
<div class="sourceCode" id="cb21"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb21-1"><a href="#cb21-1" aria-hidden="true" tabindex="-1"></a><span class="fu">names</span>(mtDT)</span></code></pre></div>
<pre><code>## [1] "carname" "mpg" "cyl" "disp" "hp" "drat" "wt"
## [8] "qsec" "vs" "am" "gear" "carb"</code></pre>
<div class="sourceCode" id="cb23"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb23-1"><a href="#cb23-1" aria-hidden="true" tabindex="-1"></a><span class="fu">dim</span>(mtDT)</span></code></pre></div>
<pre><code>## [1] 32 12</code></pre>
<div class="sourceCode" id="cb25"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb25-1"><a href="#cb25-1" aria-hidden="true" tabindex="-1"></a><span class="fu">str</span>(mtDT)</span></code></pre></div>
<pre><code>## Classes 'data.table' and 'data.frame': 32 obs. of 12 variables:
## $ carname: chr "Mazda RX4" "Mazda RX4 Wag" "Datsun 710" "Hornet 4 Drive" ...
## $ mpg : num 4.58 4.58 4.77 4.63 4.32 ...
## $ cyl : int 6 6 4 6 8 6 8 4 4 6 ...
## $ disp : num 160 160 108 258 360 ...
## $ hp : int 110 110 93 110 175 105 245 62 95 123 ...
## $ drat : num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
## $ wt : num 2.62 2.88 2.32 3.21 3.44 ...
## $ qsec : num 16.5 17 18.6 19.4 17 ...
## $ vs : int 0 0 1 1 0 1 0 1 1 1 ...
## $ am : int 1 1 1 0 0 0 0 0 0 0 ...
## $ gear : int 4 4 4 3 3 3 3 4 4 4 ...
## $ carb : int 4 4 1 1 2 1 4 2 2 4 ...
## - attr(*, ".internal.selfref")=<externalptr></code></pre>
<p>For reference, the <code>mt</code> data has the following variables:</p>
<ul>
<li>[, 1] <strong>carname</strong> - Car name</li>
<li>[, 2] <strong>mpg</strong> - Miles/(US) gallon</li>
<li>[, 3] <strong>cyl</strong> - Number of cylinders</li>
<li>[, 4] <strong>disp</strong> - Displacement (cu.in.)</li>
<li>[, 5] <strong>hp</strong> - Gross horsepower</li>
<li>[, 6] <strong>drat</strong> - Rear axle ratio</li>
<li>[, 7] <strong>wt</strong> - Weight (1000 lbs)</li>
<li>[, 8] <strong>qsec</strong> - 1/4 mile time</li>
<li>[, 9] <strong>vs</strong> - Engine (0 = V-shaped, 1 = straight)</li>
<li>[,10] <strong>am</strong> - Transmission (0 = automatic, 1 = manual)</li>
<li>[,11] <strong>gear</strong> - Number of forward gears</li>
<li>[,12] <strong>carb</strong> - Number of carburetors</li>
</ul>
</div>
</div>
<div id="data-manipulation" class="section level1">
<h1>Data manipulation 🚗</h1>
<p>When compared to a data frame, the basic arguments within brackets are <strong>NOT</strong> row and column numbers but rather “i”, “j” and “by”.</p>
<p>For example, a data table named DT, DT[i, j, by] translates to “Take DT, subset rows using <strong>i</strong>, then calculate <strong>j</strong> grouped by <strong>by</strong>”.</p>
<p>Use data.table subset [ operator the same way you would use data.frame one, but…</p>
<ul>
<li>no need to prefix each column with DT$ (like subset() and with() but built-in)</li>
<li>any R expression using any package is allowed in j argument, not just list of columns</li>
<li>extra argument by to compute j expression by group</li>
</ul>
<p><img src="pics/data_table_syntax.png" width="50%" style="display: block; margin: auto;" /></p>
<p>Let’s compare filtering using conditional statements in a data frame vs. in a data table. You will notice one of the primary benefits of data table, you only need to pass the column names!</p>
<div class="sourceCode" id="cb27"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb27-1"><a href="#cb27-1" aria-hidden="true" tabindex="-1"></a>mt[mt<span class="sc">$</span>cyl <span class="sc">==</span> <span class="dv">6</span> <span class="sc">&</span> mt<span class="sc">$</span>gear <span class="sc">==</span> <span class="dv">4</span>, ]</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>
<th align="right">qsec</th>
<th align="right">vs</th>
<th align="right">am</th>
<th align="right">gear</th>
<th align="right">carb</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Mazda RX4</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160.0</td>
<td align="right">110</td>
<td align="right">3.90</td>
<td align="right">2.620</td>
<td align="right">16.46</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="even">
<td align="left">Mazda RX4 Wag</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160.0</td>
<td align="right">110</td>
<td align="right">3.90</td>
<td align="right">2.875</td>
<td align="right">17.02</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="odd">
<td align="left">Merc 280</td>
<td align="right">4.381780</td>
<td align="right">6</td>
<td align="right">167.6</td>
<td align="right">123</td>
<td align="right">3.92</td>
<td align="right">3.440</td>
<td align="right">18.30</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="even">
<td align="left">Merc 280C</td>
<td align="right">4.219005</td>
<td align="right">6</td>
<td align="right">167.6</td>
<td align="right">123</td>
<td align="right">3.92</td>
<td align="right">3.440</td>
<td align="right">18.90</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
</tbody>
</table>
</div>
<div class="sourceCode" id="cb28"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb28-1"><a href="#cb28-1" aria-hidden="true" tabindex="-1"></a><span class="co"># datatable syntax</span></span>
<span id="cb28-2"><a href="#cb28-2" aria-hidden="true" tabindex="-1"></a>mtDT[cyl<span class="sc">==</span><span class="dv">6</span> <span class="sc">&</span> gear<span class="sc">==</span><span class="dv">4</span>, ]</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>
<th align="right">qsec</th>
<th align="right">vs</th>
<th align="right">am</th>
<th align="right">gear</th>
<th align="right">carb</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Mazda RX4</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160.0</td>
<td align="right">110</td>
<td align="right">3.90</td>
<td align="right">2.620</td>
<td align="right">16.46</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="even">
<td align="left">Mazda RX4 Wag</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160.0</td>
<td align="right">110</td>
<td align="right">3.90</td>
<td align="right">2.875</td>
<td align="right">17.02</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="odd">
<td align="left">Merc 280</td>
<td align="right">4.381780</td>
<td align="right">6</td>
<td align="right">167.6</td>
<td align="right">123</td>
<td align="right">3.92</td>
<td align="right">3.440</td>
<td align="right">18.30</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="even">
<td align="left">Merc 280C</td>
<td align="right">4.219005</td>
<td align="right">6</td>
<td align="right">167.6</td>
<td align="right">123</td>
<td align="right">3.92</td>
<td align="right">3.440</td>
<td align="right">18.90</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
</tbody>
</table>
</div>
<div id="filtering-rows" class="section level2">
<h2>Filtering rows</h2>
<p>Selecting rows is largely similar to data frame.</p>
<div class="sourceCode" id="cb29"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb29-1"><a href="#cb29-1" aria-hidden="true" tabindex="-1"></a><span class="co"># select a row</span></span>
<span id="cb29-2"><a href="#cb29-2" aria-hidden="true" tabindex="-1"></a>mtDT[<span class="dv">1</span>,]</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>
<th align="right">qsec</th>
<th align="right">vs</th>
<th align="right">am</th>
<th align="right">gear</th>
<th align="right">carb</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Mazda RX4</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160</td>
<td align="right">110</td>
<td align="right">3.9</td>
<td align="right">2.62</td>
<td align="right">16.46</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
</tbody>
</table>
</div>
<div class="sourceCode" id="cb30"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb30-1"><a href="#cb30-1" aria-hidden="true" tabindex="-1"></a><span class="co"># selecting first five rows</span></span>
<span id="cb30-2"><a href="#cb30-2" aria-hidden="true" tabindex="-1"></a>mtDT[<span class="dv">1</span><span class="sc">:</span><span class="dv">5</span>,]</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>
<th align="right">qsec</th>
<th align="right">vs</th>
<th align="right">am</th>
<th align="right">gear</th>
<th align="right">carb</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Mazda RX4</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160</td>
<td align="right">110</td>
<td align="right">3.90</td>
<td align="right">2.620</td>
<td align="right">16.46</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="even">
<td align="left">Mazda RX4 Wag</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160</td>
<td align="right">110</td>
<td align="right">3.90</td>
<td align="right">2.875</td>
<td align="right">17.02</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="odd">
<td align="left">Datsun 710</td>
<td align="right">4.774935</td>
<td align="right">4</td>
<td align="right">108</td>
<td align="right">93</td>
<td align="right">3.85</td>
<td align="right">2.320</td>
<td align="right">18.61</td>
<td align="right">1</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">1</td>
</tr>
<tr class="even">
<td align="left">Hornet 4 Drive</td>
<td align="right">4.626013</td>
<td align="right">6</td>
<td align="right">258</td>
<td align="right">110</td>
<td align="right">3.08</td>
<td align="right">3.215</td>
<td align="right">19.44</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">3</td>
<td align="right">1</td>
</tr>
<tr class="odd">
<td align="left">Hornet Sportabout</td>
<td align="right">4.324350</td>
<td align="right">8</td>
<td align="right">360</td>
<td align="right">175</td>
<td align="right">3.15</td>
<td align="right">3.440</td>
<td align="right">17.02</td>
<td align="right">0</td>
<td align="right">0</td>
<td align="right">3</td>
<td align="right">2</td>
</tr>
</tbody>
</table>
</div>
<div class="sourceCode" id="cb31"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb31-1"><a href="#cb31-1" aria-hidden="true" tabindex="-1"></a><span class="co"># no need to put comma in selecting rows</span></span>
<span id="cb31-2"><a href="#cb31-2" aria-hidden="true" tabindex="-1"></a>mtDT[<span class="dv">1</span><span class="sc">:</span><span class="dv">2</span>]</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>
<th align="right">qsec</th>
<th align="right">vs</th>
<th align="right">am</th>
<th align="right">gear</th>
<th align="right">carb</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Mazda RX4</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160</td>
<td align="right">110</td>
<td align="right">3.9</td>
<td align="right">2.620</td>
<td align="right">16.46</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
<tr class="even">
<td align="left">Mazda RX4 Wag</td>
<td align="right">4.582576</td>
<td align="right">6</td>
<td align="right">160</td>
<td align="right">110</td>
<td align="right">3.9</td>
<td align="right">2.875</td>
<td align="right">17.02</td>
<td align="right">0</td>
<td align="right">1</td>
<td align="right">4</td>
<td align="right">4</td>
</tr>
</tbody>
</table>
</div>
<div class="sourceCode" id="cb32"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb32-1"><a href="#cb32-1" aria-hidden="true" tabindex="-1"></a><span class="co"># subsetting using conditional statements</span></span>
<span id="cb32-2"><a href="#cb32-2" aria-hidden="true" tabindex="-1"></a>mtDT[cyl <span class="sc"><</span> <span class="dv">5</span> <span class="sc">&</span> am <span class="sc">==</span> <span class="dv">0</span>]</span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>
<th align="right">qsec</th>
<th align="right">vs</th>
<th align="right">am</th>
<th align="right">gear</th>
<th align="right">carb</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">Merc 240D</td>
<td align="right">4.939636</td>
<td align="right">4</td>
<td align="right">146.7</td>
<td align="right">62</td>
<td align="right">3.69</td>
<td align="right">3.190</td>
<td align="right">20.00</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">4</td>
<td align="right">2</td>
</tr>
<tr class="even">
<td align="left">Merc 230</td>
<td align="right">4.774935</td>
<td align="right">4</td>
<td align="right">140.8</td>
<td align="right">95</td>
<td align="right">3.92</td>
<td align="right">3.150</td>
<td align="right">22.90</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">4</td>
<td align="right">2</td>
</tr>
<tr class="odd">
<td align="left">Toyota Corona</td>
<td align="right">4.636809</td>
<td align="right">4</td>
<td align="right">120.1</td>
<td align="right">97</td>
<td align="right">3.70</td>
<td align="right">2.465</td>
<td align="right">20.01</td>
<td align="right">1</td>
<td align="right">0</td>
<td align="right">3</td>
<td align="right">1</td>
</tr>
</tbody>
</table>
</div>
<div class="sourceCode" id="cb33"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb33-1"><a href="#cb33-1" aria-hidden="true" tabindex="-1"></a>mtDT[cyl <span class="sc">%between%</span> <span class="fu">c</span>(<span class="dv">5</span>,<span class="dv">8</span>)] <span class="co"># conditions a range of values</span></span></code></pre></div>
<div class="kable-table">
<table>
<thead>
<tr class="header">
<th align="left">carname</th>
<th align="right">mpg</th>
<th align="right">cyl</th>
<th align="right">disp</th>
<th align="right">hp</th>
<th align="right">drat</th>
<th align="right">wt</th>