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<h1><span class="header-section-number">8</span> Writing own functions</h1>
<p>The basic syntax to write functions looks like this:</p>
<div class="sourceCode" id="cb116"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb116-1" data-line-number="1">myPlus <-<span class="st"> </span><span class="cf">function</span>(a, b){</a>
<a class="sourceLine" id="cb116-2" data-line-number="2"> <span class="kw">return</span>(a <span class="op">+</span><span class="st"> </span>b)</a>
<a class="sourceLine" id="cb116-3" data-line-number="3">}</a>
<a class="sourceLine" id="cb116-4" data-line-number="4"><span class="kw">myPlus</span>(<span class="dv">1</span>,<span class="dv">2</span>)</a></code></pre></div>
<pre><code>## [1] 3</code></pre>
<p>You can use default parameters:</p>
<div class="sourceCode" id="cb118"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb118-1" data-line-number="1">myPlus <-<span class="st"> </span><span class="cf">function</span>(<span class="dt">a=</span><span class="dv">1</span>, <span class="dt">b=</span><span class="dv">1</span>){</a>
<a class="sourceLine" id="cb118-2" data-line-number="2"> <span class="kw">return</span>(a <span class="op">+</span><span class="st"> </span>b)</a>
<a class="sourceLine" id="cb118-3" data-line-number="3">}</a>
<a class="sourceLine" id="cb118-4" data-line-number="4"><span class="kw">myPlus</span>(<span class="dv">1</span>,<span class="dv">2</span>)</a></code></pre></div>
<pre><code>## [1] 3</code></pre>
<div class="sourceCode" id="cb120"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb120-1" data-line-number="1"><span class="kw">myPlus</span>()</a></code></pre></div>
<pre><code>## [1] 2</code></pre>
<p>If you want to return multiple values, you can use a named list:</p>
<div class="sourceCode" id="cb122"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb122-1" data-line-number="1">dataframe.info <-<span class="st"> </span><span class="cf">function</span>(df){</a>
<a class="sourceLine" id="cb122-2" data-line-number="2"> cells.count <-<span class="st"> </span><span class="kw">ncol</span>(df)<span class="op">*</span><span class="kw">nrow</span>(df)</a>
<a class="sourceLine" id="cb122-3" data-line-number="3"> <span class="kw">return</span>(<span class="kw">list</span>(<span class="dt">columns=</span><span class="kw">ncol</span>(df), <span class="dt">rows=</span><span class="kw">nrow</span>(df), <span class="dt">cells=</span> cells.count))</a>
<a class="sourceLine" id="cb122-4" data-line-number="4">}</a>
<a class="sourceLine" id="cb122-5" data-line-number="5"><span class="kw">dataframe.info</span>(df)</a></code></pre></div>
<pre><code>## $columns
## [1] 12
##
## $rows
## [1] 171299
##
## $cells
## [1] 2055588</code></pre>
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