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<title>第 7 章 函数 | R编程与作图</title>
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<meta property="og:description" content="上一节课我们认识了向量操作符，体会到了向量化操作的强大，事实上，向量操作符是一种函数。R 语言的强大就在于它拥有丰富的函数，这里的函数和我们高中数学中的函数 y = f(x) 没什么区别。 7.1 基础函数 R 语言内置了很多统计函数，比如对于向量x x <- c(2, 7, 8, 9, 3) 打印向量x print(x) ## [1] 2 7 8 9 3 求开方 sqrt(x) ##...">
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<li><a class="" href="index.html">前言</a></li>
<li class="book-part">R编程基础</li>
<li><a class="" href="baseR-intro-ds.html"><span class="header-section-number">1</span> R语言介绍及资料推荐</a></li>
<li><a class="" href="baseR-install.html"><span class="header-section-number">2</span> 安装与环境配置</a></li>
<li><a class="" href="baseR-objects.html"><span class="header-section-number">3</span> 对象</a></li>
<li><a class="" href="baseR-vectors.html"><span class="header-section-number">4</span> 向量</a></li>
<li><a class="" href="baseR-data-structure.html"><span class="header-section-number">5</span> 数据结构</a></li>
<li><a class="" href="baseR-operators.html"><span class="header-section-number">6</span> 运算符及向量运算</a></li>
<li><a class="active" href="baseR-functions.html"><span class="header-section-number">7</span> 函数</a></li>
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<li><a class="" href="tidyverse-ggplot2-override-aes.html"><span class="header-section-number">27</span> ggplot2之控制图例的外观</a></li>
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<li><a class="" href="tidyverse-ggplot2-pass-function-as-parameters.html"><span class="header-section-number">31</span> ggplot2中传递函数作为参数值</a></li>
<li class="book-part">可重复性文档Rmarkdown以及练习</li>
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<li><a class="" href="eda-practice.html"><span class="header-section-number">33</span> 一天一练</a></li>
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</header><main class="col-sm-12 col-md-9 col-lg-7" id="content"><div id="baseR-functions" class="section level1" number="7">
<h1>
<span class="header-section-number">第 7 章</span> 函数<a class="anchor" aria-label="anchor" href="#baseR-functions"><i class="fas fa-link"></i></a>
</h1>
<p>上一节课我们认识了向量操作符，体会到了向量化操作的强大，事实上，向量操作符是一种函数。R 语言的强大就在于它拥有丰富的函数，这里的函数和我们高中数学中的函数 <code>y = f(x)</code> 没什么区别。</p>
<div id="基础函数" class="section level2" number="7.1">
<h2>
<span class="header-section-number">7.1</span> 基础函数<a class="anchor" aria-label="anchor" href="#%E5%9F%BA%E7%A1%80%E5%87%BD%E6%95%B0"><i class="fas fa-link"></i></a>
</h2>
<p>R 语言内置了很多统计函数，比如对于向量<code>x</code></p>
<div class="sourceCode" id="cb129"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">x</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">2</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span></code></pre></div>
<p>打印向量<code>x</code></p>
<div class="sourceCode" id="cb130"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/print.html">print</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 2 7 8 9 3</code></pre>
<p>求开方</p>
<div class="sourceCode" id="cb132"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/MathFun.html">sqrt</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 1.414214 2.645751 2.828427 3.000000 1.732051</code></pre>
<p>求自然对数</p>
<div class="sourceCode" id="cb134"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/Log.html">log</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 0.6931472 1.9459101 2.0794415 2.1972246 1.0986123</code></pre>
<p>求向量元素之和</p>
<div class="sourceCode" id="cb136"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/sum.html">sum</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 29</code></pre>
<p>求向量元素的均值</p>
<div class="sourceCode" id="cb138"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 5.8</code></pre>
<p>求向量元素的标准差</p>
<div class="sourceCode" id="cb140"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/stats/sd.html">sd</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 3.114482</code></pre>
<p>找出向量元素中的最小值</p>
<div class="sourceCode" id="cb142"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/Extremes.html">min</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 2</code></pre>
<p>找出向量元素中的最大值</p>
<div class="sourceCode" id="cb144"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/Extremes.html">max</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 9</code></pre>
<p>计算向量元素的个数</p>
<div class="sourceCode" id="cb146"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/length.html">length</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 5</code></pre>
<p>对向量元素大小排序</p>
<div class="sourceCode" id="cb148"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/sort.html">sort</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] 2 3 7 8 9</code></pre>
<p>找出向量元素的唯一值，就是给出<strong>去重后</strong>的数据</p>
<div class="sourceCode" id="cb150"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">a</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="st">"a"</span>, <span class="st">"b"</span>, <span class="st">"b"</span>, <span class="st">"c"</span>, <span class="st">"d"</span>, <span class="st">"a"</span>, <span class="st">"g"</span>, <span class="st">"c"</span>, <span class="st">"d"</span><span class="op">)</span></span>
<span><span class="fu"><a href="https://rdrr.io/r/base/unique.html">unique</a></span><span class="op">(</span><span class="va">a</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] "a" "b" "c" "d" "g"</code></pre>
<p>给出向量的分位数</p>
<div class="sourceCode" id="cb152"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/stats/quantile.html">quantile</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## 0% 25% 50% 75% 100%
## 2 3 7 8 9</code></pre>
<p>判断是否为数值型/字符串型</p>
<div class="sourceCode" id="cb154"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/numeric.html">is.numeric</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] TRUE</code></pre>
<div class="sourceCode" id="cb156"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/character.html">is.character</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] FALSE</code></pre>
<p>转化成字符串型</p>
<div class="sourceCode" id="cb158"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/character.html">as.character</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] "2" "7" "8" "9" "3"</code></pre>
<div class="sourceCode" id="cb160"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="co"># as.logical(x)</span></span>
<span><span class="co"># as.numeric(x)</span></span></code></pre></div>
<p>判断向量元素是否大于5</p>
<div class="sourceCode" id="cb161"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">x</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">2</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span>
<span><span class="va">x</span> <span class="op">></span> <span class="fl">5</span></span></code></pre></div>
<pre><code>## [1] FALSE TRUE TRUE TRUE FALSE</code></pre>
<div class="sourceCode" id="cb163"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/ifelse.html">ifelse</a></span><span class="op">(</span><span class="va">x</span> <span class="op">></span> <span class="fl">5</span>, <span class="st">"big"</span>, <span class="st">"small"</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] "small" "big" "big" "big" "small"</code></pre>
</div>
<div id="向量的函数" class="section level2" number="7.2">
<h2>
<span class="header-section-number">7.2</span> 向量的函数<a class="anchor" aria-label="anchor" href="#%E5%90%91%E9%87%8F%E7%9A%84%E5%87%BD%E6%95%B0"><i class="fas fa-link"></i></a>
</h2>
<p>用在向量上的函数，可以分为向量化函数(vectorized function)和汇总类函数(summary function)，</p>
<div class="figure" style="text-align: center">
<span style="display:block;" id="fig:unnamed-chunk-18"></span>
<img src="images/vector-function.png" alt="这两类函数在 Tidyverse 框架中，应用非常广泛。" width="65%"><p class="caption">
图 7.1: 这两类函数在 Tidyverse 框架中，应用非常广泛。
</p>
</div>
<p>当然，也会有例外，比如<code><a href="https://rdrr.io/r/base/unique.html">unique()</a></code>函数，它返回的向量通常不会与输入的向量等长，既不属于向量化函数，也不属于汇总类函数。</p>
</div>
<div id="课堂练习" class="section level2" number="7.3">
<h2>
<span class="header-section-number">7.3</span> 课堂练习<a class="anchor" aria-label="anchor" href="#%E8%AF%BE%E5%A0%82%E7%BB%83%E4%B9%A0"><i class="fas fa-link"></i></a>
</h2>
<ul>
<li>向量<code>x <- c(2, 7, 8, 9, 3)</code>的平方，加上5</li>
</ul>
<div class="sourceCode" id="cb165"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">x</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">2</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span>
<span><span class="va">x</span><span class="op">^</span><span class="fl">2</span> <span class="op">+</span> <span class="fl">5</span></span></code></pre></div>
<pre><code>## [1] 9 54 69 86 14</code></pre>
<ul>
<li>向量的元素减去其均值</li>
</ul>
<div class="sourceCode" id="cb167"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">x</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">2</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span>
<span><span class="va">x</span> <span class="op">-</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] -3.8 1.2 2.2 3.2 -2.8</code></pre>
<ul>
<li>向量标准化（向量减去其均值之后，除以标准差）</li>
</ul>
<div class="sourceCode" id="cb169"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">x</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">2</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span>
<span><span class="op">(</span><span class="va">x</span> <span class="op">-</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span><span class="op">)</span> <span class="op">/</span> <span class="fu"><a href="https://rdrr.io/r/stats/sd.html">sd</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] -1.2201065 0.3852968 0.7063774 1.0274581 -0.8990258</code></pre>
<ul>
<li>如果想对更多的向量，也做标准化处理呢？</li>
</ul>
<div class="sourceCode" id="cb171"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">y</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">1</span>, <span class="fl">5</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span>
<span><span class="op">(</span><span class="va">y</span> <span class="op">-</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">y</span><span class="op">)</span><span class="op">)</span> <span class="op">/</span> <span class="fu"><a href="https://rdrr.io/r/stats/sd.html">sd</a></span><span class="op">(</span><span class="va">y</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] -1.4599928 -0.1622214 0.4866643 0.8111071 1.1355499 -0.8111071</code></pre>
<div class="sourceCode" id="cb173"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">z</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">4</span>, <span class="fl">7</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span>, <span class="fl">9</span>, <span class="fl">6</span><span class="op">)</span></span>
<span><span class="op">(</span><span class="va">z</span> <span class="op">-</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">z</span><span class="op">)</span><span class="op">)</span> <span class="op">/</span> <span class="fu"><a href="https://rdrr.io/r/stats/sd.html">sd</a></span><span class="op">(</span><span class="va">z</span><span class="op">)</span></span></code></pre></div>
<pre><code>## [1] -1.1932699 0.1704671 0.1704671 0.6250461 1.0796251 -1.6478489 1.0796251
## [8] -0.2841119</code></pre>
<p>简单重复比较累，有没有一劳永逸的方法？</p>
</div>
<div id="自定义函数" class="section level2" number="7.4">
<h2>
<span class="header-section-number">7.4</span> 自定义函数<a class="anchor" aria-label="anchor" href="#%E8%87%AA%E5%AE%9A%E4%B9%89%E5%87%BD%E6%95%B0"><i class="fas fa-link"></i></a>
</h2>
<div class="sourceCode" id="cb175"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">my_std</span> <span class="op"><-</span> <span class="kw">function</span><span class="op">(</span><span class="va">x</span><span class="op">)</span> <span class="op">{</span></span>
<span> <span class="va">res</span> <span class="op"><-</span> <span class="op">(</span><span class="va">x</span> <span class="op">-</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html">mean</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span><span class="op">)</span> <span class="op">/</span> <span class="fu"><a href="https://rdrr.io/r/stats/sd.html">sd</a></span><span class="op">(</span><span class="va">x</span><span class="op">)</span></span>
<span> <span class="kw"><a href="https://rdrr.io/r/base/function.html">return</a></span><span class="op">(</span><span class="va">res</span><span class="op">)</span></span>
<span> <span class="op">}</span></span></code></pre></div>
<div class="sourceCode" id="cb176"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">my_std</span> <span class="op"><-</span> <span class="kw">function</span><span class="op">(</span><span class="va">x</span><span class="op">)</span> <span class="op">{</span></span>
<span> <span class="va">...</span></span>
<span><span class="op">}</span></span></code></pre></div>
<ul>
<li>创建，由<code>function(...)</code>创建一个函数</li>
<li>参数，由<code>(...)</code> 里指定参数，比如<code>function(x)</code>中的参数为 <code>x</code>
</li>
<li>函数主体，一般情况下，在<code>function(...)</code>后跟随一对大括号<code><a href="https://rdrr.io/r/base/Paren.html">{ }</a></code>，在大括号里声明具体函数功能，在代码最后一行，可以用<code>return</code>返回计算后的值。当然，如果函数的目的只是返回最后一行代码计算的值，这个<code>return</code>可以省略。</li>
<li>函数名，<code>function() { }</code> 赋值给新对象，比如这里的<code>my_std</code>，相当于给函数取一名字，方便以后使用。</li>
<li>函数调用，现在这个函数名字叫<code>my_std</code>，需要用这个函数的时候，就调用它的名字<code>my_std()</code>。</li>
</ul>
<div class="sourceCode" id="cb177"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu">my_std</span><span class="op">(</span>x <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">1</span>, <span class="fl">5</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span><span class="op">)</span> <span class="co"># 或者</span></span>
<span><span class="fu">my_std</span><span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">1</span>, <span class="fl">5</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span><span class="op">)</span> <span class="co"># 或者</span></span>
<span></span>
<span><span class="va">input</span> <span class="op"><-</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html">c</a></span><span class="op">(</span><span class="fl">1</span>, <span class="fl">5</span>, <span class="fl">7</span>, <span class="fl">8</span>, <span class="fl">9</span>, <span class="fl">3</span><span class="op">)</span></span>
<span><span class="fu">my_std</span><span class="op">(</span><span class="va">input</span><span class="op">)</span></span></code></pre></div>
</div>
<div id="使用宏包的函数" class="section level2" number="7.5">
<h2>
<span class="header-section-number">7.5</span> 使用宏包的函数<a class="anchor" aria-label="anchor" href="#%E4%BD%BF%E7%94%A8%E5%AE%8F%E5%8C%85%E7%9A%84%E5%87%BD%E6%95%B0"><i class="fas fa-link"></i></a>
</h2>
<div id="安装宏包与使用宏包" class="section level3" number="7.5.1">
<h3>
<span class="header-section-number">7.5.1</span> 安装宏包与使用宏包<a class="anchor" aria-label="anchor" href="#%E5%AE%89%E8%A3%85%E5%AE%8F%E5%8C%85%E4%B8%8E%E4%BD%BF%E7%94%A8%E5%AE%8F%E5%8C%85"><i class="fas fa-link"></i></a>
</h3>
<p>安装宏包 <code>install.packages("dplyr")</code> 相当于你买了一台电视机，安装一次就够了; 加载 <code><a href="https://dplyr.tidyverse.org">library("dplyr")</a></code>相当于你每次要看电视，就需要插上电、打开电视的动作，运行<code><a href="https://dplyr.tidyverse.org">library("dplyr")</a></code>才能用里面的函数。</p>
<div class="inline-figure"><img src="images/what-is-install.jpg" width="100%"></div>
<p>各种宏包也为我们准备了不同的函数，我们在使用前一般会先加载该宏包，比如后面章节我们会用的<code>dplyr</code>宏包中的<code><a href="https://dplyr.tidyverse.org/reference/select.html">select()</a></code>函数，它用于选取数据框的某列</p>
<div class="sourceCode" id="cb178"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="kw"><a href="https://rdrr.io/r/base/library.html">library</a></span><span class="op">(</span><span class="va"><a href="https://dplyr.tidyverse.org">dplyr</a></span><span class="op">)</span></span>
<span></span>
<span><span class="fu"><a href="https://dplyr.tidyverse.org/reference/select.html">select</a></span><span class="op">(</span><span class="va">starwars</span>, <span class="va">height</span><span class="op">)</span></span></code></pre></div>
</div>
<div id="指定函数的所属宏包" class="section level3" number="7.5.2">
<h3>
<span class="header-section-number">7.5.2</span> 指定函数的所属宏包<a class="anchor" aria-label="anchor" href="#%E6%8C%87%E5%AE%9A%E5%87%BD%E6%95%B0%E7%9A%84%E6%89%80%E5%B1%9E%E5%AE%8F%E5%8C%85"><i class="fas fa-link"></i></a>
</h3>
<p>但是，其它宏包可能也有<code><a href="https://dplyr.tidyverse.org/reference/select.html">select()</a></code>函数，比如<code>MASS</code>和<code>skimr</code>，如果同时加载了<code>dplyr</code>，<code>MASS</code>和<code>skimr</code>三个宏包，在程序中使用<code><a href="https://dplyr.tidyverse.org/reference/select.html">select()</a></code>函数，就会造成混淆和报错。这个时候就需要给每个函数指定是来源哪个宏包，具体方法就是在宏包和函数之间添加<code>::</code>，比如<code><a href="https://dplyr.tidyverse.org/reference/select.html">dplyr::select()</a></code>，<code>skimr::select()</code> 或者<code><a href="https://rdrr.io/pkg/MASS/man/lm.ridge.html">MASS::select()</a></code>。</p>
<p>至此，我们接触到了三类函数</p>
<ul>
<li><strong>内置的函数</strong></li>
<li><strong>自定义的函数</strong></li>
<li><strong>宏包的函数</strong></li>
</ul>
</div>
</div>
<div id="如何获取帮助" class="section level2" number="7.6">
<h2>
<span class="header-section-number">7.6</span> 如何获取帮助<a class="anchor" aria-label="anchor" href="#%E5%A6%82%E4%BD%95%E8%8E%B7%E5%8F%96%E5%B8%AE%E5%8A%A9"><i class="fas fa-link"></i></a>
</h2>
<ul>
<li>记住和学习所有的函数几乎是不可能的</li>
<li>打开函数的帮助页面(<code>Rstudio</code>右下面板的<code>Help</code>选项卡)</li>
</ul>
<div class="sourceCode" id="cb179"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="op">?</span><span class="va">sqrt</span></span>
<span><span class="op">?</span><span class="va">gather</span></span>
<span><span class="op">?</span><span class="va">ggplot2</span></span></code></pre></div>
<p>比如：</p>
<div class="inline-figure"><img src="images/Rhelp.png" width="90%"></div>
</div>
<div id="习题-3" class="section level2" number="7.7">
<h2>
<span class="header-section-number">7.7</span> 习题<a class="anchor" aria-label="anchor" href="#%E4%B9%A0%E9%A2%98-3"><i class="fas fa-link"></i></a>
</h2>
<ol style="list-style-type: decimal">
<li>根据方差的数学表达式，写出<strong>方差</strong>的计算函数，并与基础函数<code><a href="https://rdrr.io/r/stats/cor.html">var()</a></code>的结果对比</li>
</ol>
<p><span class="math display">\[
\mathrm{Var}(x) = \frac{1}{n - 1} \sum_{i=1}^n (x_i - \bar{x}) ^2
\]</span></p>
<ol start="2" style="list-style-type: decimal">
<li>自定义函数，它的作用是将输入的身高height(cm)与体重weight(kg)计算之后的BMI结果返回，BMI的计算公式为：</li>
</ol>
<p><span class="math display">\[
\mathrm{BMI} = \frac{weight(kg)}{height(m)^2}
\]</span></p>
<div class="sourceCode" id="cb180"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">get_bmi</span> <span class="op"><-</span> <span class="kw">function</span><span class="op">(</span><span class="va">height</span>, <span class="va">weight</span><span class="op">)</span> <span class="op">{</span></span>
<span> <span class="co"># ...</span></span>
<span><span class="op">}</span></span>
<span><span class="fu">get_bmi</span><span class="op">(</span><span class="fl">175</span>, <span class="fl">65</span><span class="op">)</span></span></code></pre></div>
<ol start="3" style="list-style-type: decimal">
<li>对于给定的向量 <code>vector</code>和阈值<code>threshold</code>，求出<code>vector</code>中所有大于该阈值的元素的均值</li>
</ol>
<div class="sourceCode" id="cb181"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">mean_above_threshod</span> <span class="op"><-</span> <span class="kw">function</span><span class="op">(</span><span class="va">vector</span>, <span class="va">threshold</span><span class="op">)</span> <span class="op">{</span></span>
<span> </span>
<span><span class="op">}</span></span></code></pre></div>
</div>
<div id="阅读" class="section level2" number="7.8">
<h2>
<span class="header-section-number">7.8</span> 阅读<a class="anchor" aria-label="anchor" href="#%E9%98%85%E8%AF%BB"><i class="fas fa-link"></i></a>
</h2>
<ul>
<li>推荐您阅读(<a href="https://r4ds.had.co.nz/functions.html" class="uri">https://r4ds.had.co.nz/functions.html</a>)</li>
</ul>
</div>
</div>
<div class="chapter-nav">
<div class="prev"><a href="baseR-operators.html"><span class="header-section-number">6</span> 运算符及向量运算</a></div>
<div class="next"><a href="baseR-functions-adv.html"><span class="header-section-number">8</span> 函数应用</a></div>
</div></main><div class="col-md-3 col-lg-2 d-none d-md-block sidebar sidebar-chapter">
<nav id="toc" data-toggle="toc" aria-label="On this page"><h2>On this page</h2>
<ul class="nav navbar-nav">
<li><a class="nav-link" href="#baseR-functions"><span class="header-section-number">7</span> 函数</a></li>
<li><a class="nav-link" href="#%E5%9F%BA%E7%A1%80%E5%87%BD%E6%95%B0"><span class="header-section-number">7.1</span> 基础函数</a></li>
<li><a class="nav-link" href="#%E5%90%91%E9%87%8F%E7%9A%84%E5%87%BD%E6%95%B0"><span class="header-section-number">7.2</span> 向量的函数</a></li>
<li><a class="nav-link" href="#%E8%AF%BE%E5%A0%82%E7%BB%83%E4%B9%A0"><span class="header-section-number">7.3</span> 课堂练习</a></li>
<li><a class="nav-link" href="#%E8%87%AA%E5%AE%9A%E4%B9%89%E5%87%BD%E6%95%B0"><span class="header-section-number">7.4</span> 自定义函数</a></li>
<li>
<a class="nav-link" href="#%E4%BD%BF%E7%94%A8%E5%AE%8F%E5%8C%85%E7%9A%84%E5%87%BD%E6%95%B0"><span class="header-section-number">7.5</span> 使用宏包的函数</a><ul class="nav navbar-nav">
<li><a class="nav-link" href="#%E5%AE%89%E8%A3%85%E5%AE%8F%E5%8C%85%E4%B8%8E%E4%BD%BF%E7%94%A8%E5%AE%8F%E5%8C%85"><span class="header-section-number">7.5.1</span> 安装宏包与使用宏包</a></li>
<li><a class="nav-link" href="#%E6%8C%87%E5%AE%9A%E5%87%BD%E6%95%B0%E7%9A%84%E6%89%80%E5%B1%9E%E5%AE%8F%E5%8C%85"><span class="header-section-number">7.5.2</span> 指定函数的所属宏包</a></li>
</ul>
</li>
<li><a class="nav-link" href="#%E5%A6%82%E4%BD%95%E8%8E%B7%E5%8F%96%E5%B8%AE%E5%8A%A9"><span class="header-section-number">7.6</span> 如何获取帮助</a></li>
<li><a class="nav-link" href="#%E4%B9%A0%E9%A2%98-3"><span class="header-section-number">7.7</span> 习题</a></li>
<li><a class="nav-link" href="#%E9%98%85%E8%AF%BB"><span class="header-section-number">7.8</span> 阅读</a></li>
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<p>"<strong>R编程与作图</strong>" was written by Suoqin Jin. It was last built on 2023-11-22.</p>
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