639 lines
38 KiB
HTML
639 lines
38 KiB
HTML
<!DOCTYPE html>
|
||
|
||
<html>
|
||
|
||
<head>
|
||
|
||
<meta charset="utf-8" />
|
||
<meta name="generator" content="pandoc" />
|
||
<meta http-equiv="X-UA-Compatible" content="IE=EDGE" />
|
||
|
||
<meta name="viewport" content="width=device-width, initial-scale=1" />
|
||
|
||
|
||
|
||
<title>Introduction to glue</title>
|
||
|
||
<script>// Pandoc 2.9 adds attributes on both header and div. We remove the former (to
|
||
// be compatible with the behavior of Pandoc < 2.8).
|
||
document.addEventListener('DOMContentLoaded', function(e) {
|
||
var hs = document.querySelectorAll("div.section[class*='level'] > :first-child");
|
||
var i, h, a;
|
||
for (i = 0; i < hs.length; i++) {
|
||
h = hs[i];
|
||
if (!/^h[1-6]$/i.test(h.tagName)) continue; // it should be a header h1-h6
|
||
a = h.attributes;
|
||
while (a.length > 0) h.removeAttribute(a[0].name);
|
||
}
|
||
});
|
||
</script>
|
||
|
||
<style type="text/css">
|
||
code{white-space: pre-wrap;}
|
||
span.smallcaps{font-variant: small-caps;}
|
||
span.underline{text-decoration: underline;}
|
||
div.column{display: inline-block; vertical-align: top; width: 50%;}
|
||
div.hanging-indent{margin-left: 1.5em; text-indent: -1.5em;}
|
||
ul.task-list{list-style: none;}
|
||
</style>
|
||
|
||
|
||
|
||
<style type="text/css">
|
||
code {
|
||
white-space: pre;
|
||
}
|
||
.sourceCode {
|
||
overflow: visible;
|
||
}
|
||
</style>
|
||
<style type="text/css" data-origin="pandoc">
|
||
pre > code.sourceCode { white-space: pre; position: relative; }
|
||
pre > code.sourceCode > span { line-height: 1.25; }
|
||
pre > code.sourceCode > span:empty { height: 1.2em; }
|
||
.sourceCode { overflow: visible; }
|
||
code.sourceCode > span { color: inherit; text-decoration: inherit; }
|
||
div.sourceCode { margin: 1em 0; }
|
||
pre.sourceCode { margin: 0; }
|
||
@media screen {
|
||
div.sourceCode { overflow: auto; }
|
||
}
|
||
@media print {
|
||
pre > code.sourceCode { white-space: pre-wrap; }
|
||
pre > code.sourceCode > span { display: inline-block; text-indent: -5em; padding-left: 5em; }
|
||
}
|
||
pre.numberSource code
|
||
{ counter-reset: source-line 0; }
|
||
pre.numberSource code > span
|
||
{ position: relative; left: -4em; counter-increment: source-line; }
|
||
pre.numberSource code > span > a:first-child::before
|
||
{ content: counter(source-line);
|
||
position: relative; left: -1em; text-align: right; vertical-align: baseline;
|
||
border: none; display: inline-block;
|
||
-webkit-touch-callout: none; -webkit-user-select: none;
|
||
-khtml-user-select: none; -moz-user-select: none;
|
||
-ms-user-select: none; user-select: none;
|
||
padding: 0 4px; width: 4em;
|
||
color: #aaaaaa;
|
||
}
|
||
pre.numberSource { margin-left: 3em; border-left: 1px solid #aaaaaa; padding-left: 4px; }
|
||
div.sourceCode
|
||
{ }
|
||
@media screen {
|
||
pre > code.sourceCode > span > a:first-child::before { text-decoration: underline; }
|
||
}
|
||
code span.al { color: #ff0000; font-weight: bold; }
|
||
code span.an { color: #60a0b0; font-weight: bold; font-style: italic; }
|
||
code span.at { color: #7d9029; }
|
||
code span.bn { color: #40a070; }
|
||
code span.bu { color: #008000; }
|
||
code span.cf { color: #007020; font-weight: bold; }
|
||
code span.ch { color: #4070a0; }
|
||
code span.cn { color: #880000; }
|
||
code span.co { color: #60a0b0; font-style: italic; }
|
||
code span.cv { color: #60a0b0; font-weight: bold; font-style: italic; }
|
||
code span.do { color: #ba2121; font-style: italic; }
|
||
code span.dt { color: #902000; }
|
||
code span.dv { color: #40a070; }
|
||
code span.er { color: #ff0000; font-weight: bold; }
|
||
code span.ex { }
|
||
code span.fl { color: #40a070; }
|
||
code span.fu { color: #06287e; }
|
||
code span.im { color: #008000; font-weight: bold; }
|
||
code span.in { color: #60a0b0; font-weight: bold; font-style: italic; }
|
||
code span.kw { color: #007020; font-weight: bold; }
|
||
code span.op { color: #666666; }
|
||
code span.ot { color: #007020; }
|
||
code span.pp { color: #bc7a00; }
|
||
code span.sc { color: #4070a0; }
|
||
code span.ss { color: #bb6688; }
|
||
code span.st { color: #4070a0; }
|
||
code span.va { color: #19177c; }
|
||
code span.vs { color: #4070a0; }
|
||
code span.wa { color: #60a0b0; font-weight: bold; font-style: italic; }
|
||
</style>
|
||
<script>
|
||
// apply pandoc div.sourceCode style to pre.sourceCode instead
|
||
(function() {
|
||
var sheets = document.styleSheets;
|
||
for (var i = 0; i < sheets.length; i++) {
|
||
if (sheets[i].ownerNode.dataset["origin"] !== "pandoc") continue;
|
||
try { var rules = sheets[i].cssRules; } catch (e) { continue; }
|
||
var j = 0;
|
||
while (j < rules.length) {
|
||
var rule = rules[j];
|
||
// check if there is a div.sourceCode rule
|
||
if (rule.type !== rule.STYLE_RULE || rule.selectorText !== "div.sourceCode") {
|
||
j++;
|
||
continue;
|
||
}
|
||
var style = rule.style.cssText;
|
||
// check if color or background-color is set
|
||
if (rule.style.color === '' && rule.style.backgroundColor === '') {
|
||
j++;
|
||
continue;
|
||
}
|
||
// replace div.sourceCode by a pre.sourceCode rule
|
||
sheets[i].deleteRule(j);
|
||
sheets[i].insertRule('pre.sourceCode{' + style + '}', j);
|
||
}
|
||
}
|
||
})();
|
||
</script>
|
||
|
||
|
||
|
||
|
||
<style type="text/css">body {
|
||
background-color: #fff;
|
||
margin: 1em auto;
|
||
max-width: 700px;
|
||
overflow: visible;
|
||
padding-left: 2em;
|
||
padding-right: 2em;
|
||
font-family: "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;
|
||
font-size: 14px;
|
||
line-height: 1.35;
|
||
}
|
||
#TOC {
|
||
clear: both;
|
||
margin: 0 0 10px 10px;
|
||
padding: 4px;
|
||
width: 400px;
|
||
border: 1px solid #CCCCCC;
|
||
border-radius: 5px;
|
||
background-color: #f6f6f6;
|
||
font-size: 13px;
|
||
line-height: 1.3;
|
||
}
|
||
#TOC .toctitle {
|
||
font-weight: bold;
|
||
font-size: 15px;
|
||
margin-left: 5px;
|
||
}
|
||
#TOC ul {
|
||
padding-left: 40px;
|
||
margin-left: -1.5em;
|
||
margin-top: 5px;
|
||
margin-bottom: 5px;
|
||
}
|
||
#TOC ul ul {
|
||
margin-left: -2em;
|
||
}
|
||
#TOC li {
|
||
line-height: 16px;
|
||
}
|
||
table {
|
||
margin: 1em auto;
|
||
border-width: 1px;
|
||
border-color: #DDDDDD;
|
||
border-style: outset;
|
||
border-collapse: collapse;
|
||
}
|
||
table th {
|
||
border-width: 2px;
|
||
padding: 5px;
|
||
border-style: inset;
|
||
}
|
||
table td {
|
||
border-width: 1px;
|
||
border-style: inset;
|
||
line-height: 18px;
|
||
padding: 5px 5px;
|
||
}
|
||
table, table th, table td {
|
||
border-left-style: none;
|
||
border-right-style: none;
|
||
}
|
||
table thead, table tr.even {
|
||
background-color: #f7f7f7;
|
||
}
|
||
p {
|
||
margin: 0.5em 0;
|
||
}
|
||
blockquote {
|
||
background-color: #f6f6f6;
|
||
padding: 0.25em 0.75em;
|
||
}
|
||
hr {
|
||
border-style: solid;
|
||
border: none;
|
||
border-top: 1px solid #777;
|
||
margin: 28px 0;
|
||
}
|
||
dl {
|
||
margin-left: 0;
|
||
}
|
||
dl dd {
|
||
margin-bottom: 13px;
|
||
margin-left: 13px;
|
||
}
|
||
dl dt {
|
||
font-weight: bold;
|
||
}
|
||
ul {
|
||
margin-top: 0;
|
||
}
|
||
ul li {
|
||
list-style: circle outside;
|
||
}
|
||
ul ul {
|
||
margin-bottom: 0;
|
||
}
|
||
pre, code {
|
||
background-color: #f7f7f7;
|
||
border-radius: 3px;
|
||
color: #333;
|
||
white-space: pre-wrap;
|
||
}
|
||
pre {
|
||
border-radius: 3px;
|
||
margin: 5px 0px 10px 0px;
|
||
padding: 10px;
|
||
}
|
||
pre:not([class]) {
|
||
background-color: #f7f7f7;
|
||
}
|
||
code {
|
||
font-family: Consolas, Monaco, 'Courier New', monospace;
|
||
font-size: 85%;
|
||
}
|
||
p > code, li > code {
|
||
padding: 2px 0px;
|
||
}
|
||
div.figure {
|
||
text-align: center;
|
||
}
|
||
img {
|
||
background-color: #FFFFFF;
|
||
padding: 2px;
|
||
border: 1px solid #DDDDDD;
|
||
border-radius: 3px;
|
||
border: 1px solid #CCCCCC;
|
||
margin: 0 5px;
|
||
}
|
||
h1 {
|
||
margin-top: 0;
|
||
font-size: 35px;
|
||
line-height: 40px;
|
||
}
|
||
h2 {
|
||
border-bottom: 4px solid #f7f7f7;
|
||
padding-top: 10px;
|
||
padding-bottom: 2px;
|
||
font-size: 145%;
|
||
}
|
||
h3 {
|
||
border-bottom: 2px solid #f7f7f7;
|
||
padding-top: 10px;
|
||
font-size: 120%;
|
||
}
|
||
h4 {
|
||
border-bottom: 1px solid #f7f7f7;
|
||
margin-left: 8px;
|
||
font-size: 105%;
|
||
}
|
||
h5, h6 {
|
||
border-bottom: 1px solid #ccc;
|
||
font-size: 105%;
|
||
}
|
||
a {
|
||
color: #0033dd;
|
||
text-decoration: none;
|
||
}
|
||
a:hover {
|
||
color: #6666ff; }
|
||
a:visited {
|
||
color: #800080; }
|
||
a:visited:hover {
|
||
color: #BB00BB; }
|
||
a[href^="http:"] {
|
||
text-decoration: underline; }
|
||
a[href^="https:"] {
|
||
text-decoration: underline; }
|
||
|
||
code > span.kw { color: #555; font-weight: bold; }
|
||
code > span.dt { color: #902000; }
|
||
code > span.dv { color: #40a070; }
|
||
code > span.bn { color: #d14; }
|
||
code > span.fl { color: #d14; }
|
||
code > span.ch { color: #d14; }
|
||
code > span.st { color: #d14; }
|
||
code > span.co { color: #888888; font-style: italic; }
|
||
code > span.ot { color: #007020; }
|
||
code > span.al { color: #ff0000; font-weight: bold; }
|
||
code > span.fu { color: #900; font-weight: bold; }
|
||
code > span.er { color: #a61717; background-color: #e3d2d2; }
|
||
</style>
|
||
|
||
|
||
|
||
|
||
</head>
|
||
|
||
<body>
|
||
|
||
|
||
|
||
|
||
<h1 class="title toc-ignore">Introduction to glue</h1>
|
||
|
||
|
||
|
||
<p>The glue package contains functions for string interpolation: gluing
|
||
together character strings and R code.</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>(glue)</span></code></pre></div>
|
||
<div id="gluing-and-interpolating" class="section level2">
|
||
<h2>Gluing and interpolating</h2>
|
||
<p><code>glue()</code> can be used to glue together pieces of text:</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><span class="fu">glue</span>(<span class="st">"glue "</span>, <span class="st">"some "</span>, <span class="st">"text "</span>, <span class="st">"together"</span>)</span>
|
||
<span id="cb2-2"><a href="#cb2-2" tabindex="-1"></a><span class="co">#> glue some text together</span></span></code></pre></div>
|
||
<p>But glue’s real power comes with <code>{}</code>: anything inside of
|
||
<code>{}</code> is evaluated and pasted into the string. This makes it
|
||
easy to interpolate variables:</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>name <span class="ot"><-</span> <span class="st">"glue"</span></span>
|
||
<span id="cb3-2"><a href="#cb3-2" tabindex="-1"></a><span class="fu">glue</span>(<span class="st">"We are learning how to use the {name} R package."</span>)</span>
|
||
<span id="cb3-3"><a href="#cb3-3" tabindex="-1"></a><span class="co">#> We are learning how to use the glue R package.</span></span></code></pre></div>
|
||
<p>As well as more complex expressions:</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>release_date <span class="ot"><-</span> <span class="fu">as.Date</span>(<span class="st">"2017-06-13"</span>)</span>
|
||
<span id="cb4-2"><a href="#cb4-2" tabindex="-1"></a><span class="fu">glue</span>(<span class="st">"Release was on a {format(release_date, '%A')}."</span>)</span>
|
||
<span id="cb4-3"><a href="#cb4-3" tabindex="-1"></a><span class="co">#> Release was on a Tuesday.</span></span></code></pre></div>
|
||
</div>
|
||
<div id="control-of-line-breaks" class="section level2">
|
||
<h2>Control of line breaks</h2>
|
||
<p><code>glue()</code> honors the line breaks in its input:</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><span class="fu">glue</span>(<span class="st">"</span></span>
|
||
<span id="cb5-2"><a href="#cb5-2" tabindex="-1"></a><span class="st"> A formatted string</span></span>
|
||
<span id="cb5-3"><a href="#cb5-3" tabindex="-1"></a><span class="st"> Can have multiple lines</span></span>
|
||
<span id="cb5-4"><a href="#cb5-4" tabindex="-1"></a><span class="st"> with additional indention preserved</span></span>
|
||
<span id="cb5-5"><a href="#cb5-5" tabindex="-1"></a><span class="st"> "</span></span>
|
||
<span id="cb5-6"><a href="#cb5-6" tabindex="-1"></a>)</span>
|
||
<span id="cb5-7"><a href="#cb5-7" tabindex="-1"></a><span class="co">#> A formatted string</span></span>
|
||
<span id="cb5-8"><a href="#cb5-8" tabindex="-1"></a><span class="co">#> Can have multiple lines</span></span>
|
||
<span id="cb5-9"><a href="#cb5-9" tabindex="-1"></a><span class="co">#> with additional indention preserved</span></span></code></pre></div>
|
||
<p>The example above demonstrates some other important facts about the
|
||
pre-processing of the template string:</p>
|
||
<ul>
|
||
<li>An empty first or last line is automatically trimmed.</li>
|
||
<li>Leading whitespace that is common across all lines is trimmed.</li>
|
||
</ul>
|
||
<p>The elimination of common leading whitespace is advantageous, because
|
||
you aren’t forced to choose between indenting your code normally and
|
||
getting the output you actually want. This is easier to appreciate when
|
||
you have <code>glue()</code> inside a function body (this example also
|
||
shows an alternative way of styling the end of a <code>glue()</code>
|
||
call):</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>foo <span class="ot"><-</span> <span class="cf">function</span>() {</span>
|
||
<span id="cb6-2"><a href="#cb6-2" tabindex="-1"></a> <span class="fu">glue</span>(<span class="st">"</span></span>
|
||
<span id="cb6-3"><a href="#cb6-3" tabindex="-1"></a><span class="st"> A formatted string</span></span>
|
||
<span id="cb6-4"><a href="#cb6-4" tabindex="-1"></a><span class="st"> Can have multiple lines</span></span>
|
||
<span id="cb6-5"><a href="#cb6-5" tabindex="-1"></a><span class="st"> with additional indention preserved"</span>)</span>
|
||
<span id="cb6-6"><a href="#cb6-6" tabindex="-1"></a>}</span>
|
||
<span id="cb6-7"><a href="#cb6-7" tabindex="-1"></a><span class="fu">foo</span>()</span>
|
||
<span id="cb6-8"><a href="#cb6-8" tabindex="-1"></a><span class="co">#> A formatted string</span></span>
|
||
<span id="cb6-9"><a href="#cb6-9" tabindex="-1"></a><span class="co">#> Can have multiple lines</span></span>
|
||
<span id="cb6-10"><a href="#cb6-10" tabindex="-1"></a><span class="co">#> with additional indention preserved</span></span></code></pre></div>
|
||
<p>On the other hand, what if you don’t want a line break in the output,
|
||
but you also like to limit the length of lines in your source code to,
|
||
e.g., 80 characters? The first option is to use <code>\\</code> to break
|
||
the template string into multiple lines, without getting line breaks in
|
||
the output:</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>release_date <span class="ot"><-</span> <span class="fu">as.Date</span>(<span class="st">"2017-06-13"</span>)</span>
|
||
<span id="cb7-2"><a href="#cb7-2" tabindex="-1"></a><span class="fu">glue</span>(<span class="st">"</span></span>
|
||
<span id="cb7-3"><a href="#cb7-3" tabindex="-1"></a><span class="st"> The first version of the glue package was released on </span><span class="sc">\\</span></span>
|
||
<span id="cb7-4"><a href="#cb7-4" tabindex="-1"></a><span class="st"> a {format(release_date, '%A')}."</span>)</span>
|
||
<span id="cb7-5"><a href="#cb7-5" tabindex="-1"></a><span class="co">#> The first version of the glue package was released on a Tuesday.</span></span></code></pre></div>
|
||
<p>This comes up fairly often when an expression to evaluate inside
|
||
<code>{}</code> takes up more characters than its result,
|
||
i.e. <code>format(release_date, '%A')</code> versus
|
||
<code>Tuesday</code>. A second way to achieve the same result is to
|
||
break the template into individual pieces, which are then
|
||
concatenated.</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><span class="fu">glue</span>(</span>
|
||
<span id="cb8-2"><a href="#cb8-2" tabindex="-1"></a> <span class="st">"The first version of the glue package was released on "</span>,</span>
|
||
<span id="cb8-3"><a href="#cb8-3" tabindex="-1"></a> <span class="st">"a {format(release_date, '%A')}."</span></span>
|
||
<span id="cb8-4"><a href="#cb8-4" tabindex="-1"></a>)</span>
|
||
<span id="cb8-5"><a href="#cb8-5" tabindex="-1"></a><span class="co">#> The first version of the glue package was released on a Tuesday.</span></span></code></pre></div>
|
||
<p>If you want an explicit newline at the start or end, include an extra
|
||
empty line.</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><span class="co"># no leading or trailing newline</span></span>
|
||
<span id="cb9-2"><a href="#cb9-2" tabindex="-1"></a>x <span class="ot"><-</span> <span class="fu">glue</span>(<span class="st">"</span></span>
|
||
<span id="cb9-3"><a href="#cb9-3" tabindex="-1"></a><span class="st"> blah</span></span>
|
||
<span id="cb9-4"><a href="#cb9-4" tabindex="-1"></a><span class="st"> "</span>)</span>
|
||
<span id="cb9-5"><a href="#cb9-5" tabindex="-1"></a><span class="fu">unclass</span>(x)</span>
|
||
<span id="cb9-6"><a href="#cb9-6" tabindex="-1"></a><span class="co">#> [1] "blah"</span></span>
|
||
<span id="cb9-7"><a href="#cb9-7" tabindex="-1"></a></span>
|
||
<span id="cb9-8"><a href="#cb9-8" tabindex="-1"></a><span class="co"># both a leading and trailing newline</span></span>
|
||
<span id="cb9-9"><a href="#cb9-9" tabindex="-1"></a>y <span class="ot"><-</span> <span class="fu">glue</span>(<span class="st">"</span></span>
|
||
<span id="cb9-10"><a href="#cb9-10" tabindex="-1"></a></span>
|
||
<span id="cb9-11"><a href="#cb9-11" tabindex="-1"></a><span class="st"> blah</span></span>
|
||
<span id="cb9-12"><a href="#cb9-12" tabindex="-1"></a></span>
|
||
<span id="cb9-13"><a href="#cb9-13" tabindex="-1"></a><span class="st"> "</span>)</span>
|
||
<span id="cb9-14"><a href="#cb9-14" tabindex="-1"></a><span class="fu">unclass</span>(y)</span>
|
||
<span id="cb9-15"><a href="#cb9-15" tabindex="-1"></a><span class="co">#> [1] "\nblah\n"</span></span></code></pre></div>
|
||
<p>We use <code>unclass()</code> above to make it easier to see the
|
||
absence and presence of the newlines, i.e. to reveal the literal
|
||
<code>\n</code> escape sequences. <code>glue()</code> and friends
|
||
generally return a glue object, which is a character vector with the S3
|
||
class <code>"glue"</code>. The <code>"glue"</code> class exists
|
||
primarily for the sake of a print method, which displays the natural
|
||
formatted result of a glue string. Most of the time this is
|
||
<em>exactly</em> what the user wants to see. The example above happens
|
||
to be an exception, where we really do want to see the underlying string
|
||
representation.</p>
|
||
<p>Here’s another example to drive home the difference between printing
|
||
a glue object and looking at its string representation.
|
||
<code>as.character()</code> is a another way to do this that is arguably
|
||
more expressive.</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>x <span class="ot"><-</span> <span class="fu">glue</span>(<span class="st">'</span></span>
|
||
<span id="cb10-2"><a href="#cb10-2" tabindex="-1"></a><span class="st"> abc</span></span>
|
||
<span id="cb10-3"><a href="#cb10-3" tabindex="-1"></a><span class="st"> " }</span></span>
|
||
<span id="cb10-4"><a href="#cb10-4" tabindex="-1"></a></span>
|
||
<span id="cb10-5"><a href="#cb10-5" tabindex="-1"></a><span class="st"> xyz'</span>)</span>
|
||
<span id="cb10-6"><a href="#cb10-6" tabindex="-1"></a><span class="fu">class</span>(x)</span>
|
||
<span id="cb10-7"><a href="#cb10-7" tabindex="-1"></a><span class="co">#> [1] "glue" "character"</span></span>
|
||
<span id="cb10-8"><a href="#cb10-8" tabindex="-1"></a></span>
|
||
<span id="cb10-9"><a href="#cb10-9" tabindex="-1"></a>x</span>
|
||
<span id="cb10-10"><a href="#cb10-10" tabindex="-1"></a><span class="co">#> abc</span></span>
|
||
<span id="cb10-11"><a href="#cb10-11" tabindex="-1"></a><span class="co">#> " }</span></span>
|
||
<span id="cb10-12"><a href="#cb10-12" tabindex="-1"></a><span class="co">#> </span></span>
|
||
<span id="cb10-13"><a href="#cb10-13" tabindex="-1"></a><span class="co">#> xyz</span></span>
|
||
<span id="cb10-14"><a href="#cb10-14" tabindex="-1"></a><span class="fu">unclass</span>(x)</span>
|
||
<span id="cb10-15"><a href="#cb10-15" tabindex="-1"></a><span class="co">#> [1] "abc\n\"\t}\n\nxyz"</span></span>
|
||
<span id="cb10-16"><a href="#cb10-16" tabindex="-1"></a><span class="fu">as.character</span>(x)</span>
|
||
<span id="cb10-17"><a href="#cb10-17" tabindex="-1"></a><span class="co">#> [1] "abc\n\"\t}\n\nxyz"</span></span></code></pre></div>
|
||
</div>
|
||
<div id="delimiters" class="section level2">
|
||
<h2>Delimiters</h2>
|
||
<p>By default, code to be evaluated goes inside <code>{}</code> in a
|
||
glue string. If want a literal curly brace in your string, double
|
||
it:</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><span class="fu">glue</span>(<span class="st">"The name of the package is {name}, not {{name}}."</span>)</span>
|
||
<span id="cb11-2"><a href="#cb11-2" tabindex="-1"></a><span class="co">#> The name of the package is glue, not {name}.</span></span></code></pre></div>
|
||
<p>Sometimes it’s just more convenient to use different delimiters
|
||
altogether, especially if the template text comes from elsewhere or is
|
||
subject to external requirements. Consider this example where we want to
|
||
interpolate the function name into a code snippet that defines a
|
||
function:</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>fn_def <span class="ot"><-</span> <span class="st">"</span></span>
|
||
<span id="cb12-2"><a href="#cb12-2" tabindex="-1"></a><span class="st"> <<NAME>> <- function(x) {</span></span>
|
||
<span id="cb12-3"><a href="#cb12-3" tabindex="-1"></a><span class="st"> # imagine a function body here</span></span>
|
||
<span id="cb12-4"><a href="#cb12-4" tabindex="-1"></a><span class="st"> }"</span></span>
|
||
<span id="cb12-5"><a href="#cb12-5" tabindex="-1"></a><span class="fu">glue</span>(fn_def, <span class="at">NAME =</span> <span class="st">"my_function"</span>, <span class="at">.open =</span> <span class="st">"<<"</span>, <span class="at">.close =</span> <span class="st">">>"</span>)</span>
|
||
<span id="cb12-6"><a href="#cb12-6" tabindex="-1"></a><span class="co">#> my_function <- function(x) {</span></span>
|
||
<span id="cb12-7"><a href="#cb12-7" tabindex="-1"></a><span class="co">#> # imagine a function body here</span></span>
|
||
<span id="cb12-8"><a href="#cb12-8" tabindex="-1"></a><span class="co">#> }</span></span></code></pre></div>
|
||
<p>In this glue string, <code>{</code> and <code>}</code> have very
|
||
special meaning. If we forced ourselves to double them, suddenly it
|
||
doesn’t look like normal R code anymore. Using alternative delimiters is
|
||
a nice option in cases like this.</p>
|
||
</div>
|
||
<div id="where-glue-looks-for-values" class="section level2">
|
||
<h2>Where glue looks for values</h2>
|
||
<p>By default, <code>glue()</code> evaluates the code inside
|
||
<code>{}</code> in the caller environment:</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><span class="fu">glue</span>(..., <span class="at">.envir =</span> <span class="fu">parent.frame</span>())</span></code></pre></div>
|
||
<p>So, for a top-level <code>glue()</code> call, that means the global
|
||
environment.</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>x <span class="ot"><-</span> <span class="st">"the caller environment"</span></span>
|
||
<span id="cb14-2"><a href="#cb14-2" tabindex="-1"></a><span class="fu">glue</span>(<span class="st">"By default, `glue()` evaluates code in {x}."</span>)</span>
|
||
<span id="cb14-3"><a href="#cb14-3" tabindex="-1"></a><span class="co">#> By default, `glue()` evaluates code in the caller environment.</span></span></code></pre></div>
|
||
<p>But you can provide more narrowly scoped values by passing them to
|
||
<code>glue()</code> in <code>name = value</code> form:</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>x <span class="ot"><-</span> <span class="st">"the local environment"</span></span>
|
||
<span id="cb15-2"><a href="#cb15-2" tabindex="-1"></a><span class="fu">glue</span>(</span>
|
||
<span id="cb15-3"><a href="#cb15-3" tabindex="-1"></a> <span class="st">"`glue()` can access values from {x} or from {y}. {z}"</span>,</span>
|
||
<span id="cb15-4"><a href="#cb15-4" tabindex="-1"></a> <span class="at">y =</span> <span class="st">"named arguments"</span>,</span>
|
||
<span id="cb15-5"><a href="#cb15-5" tabindex="-1"></a> <span class="at">z =</span> <span class="st">"Woo!"</span></span>
|
||
<span id="cb15-6"><a href="#cb15-6" tabindex="-1"></a>)</span>
|
||
<span id="cb15-7"><a href="#cb15-7" tabindex="-1"></a><span class="co">#> `glue()` can access values from the local environment or from named arguments. Woo!</span></span></code></pre></div>
|
||
<p>If the relevant data lives in a data frame (or list or environment),
|
||
use <code>glue_data()</code> instead:</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>mini_mtcars <span class="ot"><-</span> <span class="fu">head</span>(<span class="fu">cbind</span>(<span class="at">model =</span> <span class="fu">rownames</span>(mtcars), mtcars))</span>
|
||
<span id="cb16-2"><a href="#cb16-2" tabindex="-1"></a><span class="fu">rownames</span>(mini_mtcars) <span class="ot"><-</span> <span class="cn">NULL</span></span>
|
||
<span id="cb16-3"><a href="#cb16-3" tabindex="-1"></a><span class="fu">glue_data</span>(mini_mtcars, <span class="st">"{model} has {hp} hp."</span>)</span>
|
||
<span id="cb16-4"><a href="#cb16-4" tabindex="-1"></a><span class="co">#> Mazda RX4 has 110 hp.</span></span>
|
||
<span id="cb16-5"><a href="#cb16-5" tabindex="-1"></a><span class="co">#> Mazda RX4 Wag has 110 hp.</span></span>
|
||
<span id="cb16-6"><a href="#cb16-6" tabindex="-1"></a><span class="co">#> Datsun 710 has 93 hp.</span></span>
|
||
<span id="cb16-7"><a href="#cb16-7" tabindex="-1"></a><span class="co">#> Hornet 4 Drive has 110 hp.</span></span>
|
||
<span id="cb16-8"><a href="#cb16-8" tabindex="-1"></a><span class="co">#> Hornet Sportabout has 175 hp.</span></span>
|
||
<span id="cb16-9"><a href="#cb16-9" tabindex="-1"></a><span class="co">#> Valiant has 105 hp.</span></span></code></pre></div>
|
||
<p><code>glue_data()</code> is very natural to use with the pipe:</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>mini_mtcars <span class="sc">|></span></span>
|
||
<span id="cb17-2"><a href="#cb17-2" tabindex="-1"></a> <span class="fu">glue_data</span>(<span class="st">"{model} gets {mpg} miles per gallon."</span>)</span>
|
||
<span id="cb17-3"><a href="#cb17-3" tabindex="-1"></a><span class="co">#> Mazda RX4 gets 21 miles per gallon.</span></span>
|
||
<span id="cb17-4"><a href="#cb17-4" tabindex="-1"></a><span class="co">#> Mazda RX4 Wag gets 21 miles per gallon.</span></span>
|
||
<span id="cb17-5"><a href="#cb17-5" tabindex="-1"></a><span class="co">#> Datsun 710 gets 22.8 miles per gallon.</span></span>
|
||
<span id="cb17-6"><a href="#cb17-6" tabindex="-1"></a><span class="co">#> Hornet 4 Drive gets 21.4 miles per gallon.</span></span>
|
||
<span id="cb17-7"><a href="#cb17-7" tabindex="-1"></a><span class="co">#> Hornet Sportabout gets 18.7 miles per gallon.</span></span>
|
||
<span id="cb17-8"><a href="#cb17-8" tabindex="-1"></a><span class="co">#> Valiant gets 18.1 miles per gallon.</span></span></code></pre></div>
|
||
<p>Returning to <code>glue()</code>, recall that it defaults to
|
||
evaluation in the caller environment. This has happy implications inside
|
||
a <code>dplyr::mutate()</code> pipeline. The data-masking feature of
|
||
<code>mutate()</code> means the columns of the target data frame are “in
|
||
scope” for a <code>glue()</code> call:</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><span class="fu">library</span>(dplyr)</span>
|
||
<span id="cb18-2"><a href="#cb18-2" tabindex="-1"></a></span>
|
||
<span id="cb18-3"><a href="#cb18-3" tabindex="-1"></a>mini_mtcars <span class="sc">|></span></span>
|
||
<span id="cb18-4"><a href="#cb18-4" tabindex="-1"></a> <span class="fu">mutate</span>(<span class="at">note =</span> <span class="fu">glue</span>(<span class="st">"{model} gets {mpg} miles per gallon."</span>)) <span class="sc">|></span></span>
|
||
<span id="cb18-5"><a href="#cb18-5" tabindex="-1"></a> <span class="fu">select</span>(note, cyl, disp)</span>
|
||
<span id="cb18-6"><a href="#cb18-6" tabindex="-1"></a><span class="co">#> note cyl disp</span></span>
|
||
<span id="cb18-7"><a href="#cb18-7" tabindex="-1"></a><span class="co">#> 1 Mazda RX4 gets 21 miles per gallon. 6 160</span></span>
|
||
<span id="cb18-8"><a href="#cb18-8" tabindex="-1"></a><span class="co">#> 2 Mazda RX4 Wag gets 21 miles per gallon. 6 160</span></span>
|
||
<span id="cb18-9"><a href="#cb18-9" tabindex="-1"></a><span class="co">#> 3 Datsun 710 gets 22.8 miles per gallon. 4 108</span></span>
|
||
<span id="cb18-10"><a href="#cb18-10" tabindex="-1"></a><span class="co">#> 4 Hornet 4 Drive gets 21.4 miles per gallon. 6 258</span></span>
|
||
<span id="cb18-11"><a href="#cb18-11" tabindex="-1"></a><span class="co">#> 5 Hornet Sportabout gets 18.7 miles per gallon. 8 360</span></span>
|
||
<span id="cb18-12"><a href="#cb18-12" tabindex="-1"></a><span class="co">#> 6 Valiant gets 18.1 miles per gallon. 6 225</span></span></code></pre></div>
|
||
</div>
|
||
<div id="sql" class="section level2">
|
||
<h2>SQL</h2>
|
||
<p>glue has explicit support for constructing SQL statements. Use
|
||
backticks to quote identifiers. Normal strings and numbers are quoted
|
||
appropriately for your backend.</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>con <span class="ot"><-</span> DBI<span class="sc">::</span><span class="fu">dbConnect</span>(RSQLite<span class="sc">::</span><span class="fu">SQLite</span>(), <span class="st">":memory:"</span>)</span>
|
||
<span id="cb19-2"><a href="#cb19-2" tabindex="-1"></a><span class="fu">colnames</span>(iris) <span class="ot"><-</span> <span class="fu">gsub</span>(<span class="st">"[.]"</span>, <span class="st">"_"</span>, <span class="fu">tolower</span>(<span class="fu">colnames</span>(iris)))</span>
|
||
<span id="cb19-3"><a href="#cb19-3" tabindex="-1"></a>DBI<span class="sc">::</span><span class="fu">dbWriteTable</span>(con, <span class="st">"iris"</span>, iris)</span>
|
||
<span id="cb19-4"><a href="#cb19-4" tabindex="-1"></a>var <span class="ot"><-</span> <span class="st">"sepal_width"</span></span>
|
||
<span id="cb19-5"><a href="#cb19-5" tabindex="-1"></a>tbl <span class="ot"><-</span> <span class="st">"iris"</span></span>
|
||
<span id="cb19-6"><a href="#cb19-6" tabindex="-1"></a>num <span class="ot"><-</span> <span class="dv">2</span></span>
|
||
<span id="cb19-7"><a href="#cb19-7" tabindex="-1"></a>val <span class="ot"><-</span> <span class="st">"setosa"</span></span>
|
||
<span id="cb19-8"><a href="#cb19-8" tabindex="-1"></a><span class="fu">glue_sql</span>(<span class="st">"</span></span>
|
||
<span id="cb19-9"><a href="#cb19-9" tabindex="-1"></a><span class="st"> SELECT {`var`}</span></span>
|
||
<span id="cb19-10"><a href="#cb19-10" tabindex="-1"></a><span class="st"> FROM {`tbl`}</span></span>
|
||
<span id="cb19-11"><a href="#cb19-11" tabindex="-1"></a><span class="st"> WHERE {`tbl`}.sepal_length > {num}</span></span>
|
||
<span id="cb19-12"><a href="#cb19-12" tabindex="-1"></a><span class="st"> AND {`tbl`}.species = {val}</span></span>
|
||
<span id="cb19-13"><a href="#cb19-13" tabindex="-1"></a><span class="st"> "</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb19-14"><a href="#cb19-14" tabindex="-1"></a><span class="co">#> <SQL> SELECT `sepal_width`</span></span>
|
||
<span id="cb19-15"><a href="#cb19-15" tabindex="-1"></a><span class="co">#> FROM `iris`</span></span>
|
||
<span id="cb19-16"><a href="#cb19-16" tabindex="-1"></a><span class="co">#> WHERE `iris`.sepal_length > 2</span></span>
|
||
<span id="cb19-17"><a href="#cb19-17" tabindex="-1"></a><span class="co">#> AND `iris`.species = 'setosa'</span></span></code></pre></div>
|
||
<p><code>glue_sql()</code> can be used in conjunction with parameterized
|
||
queries using <code>DBI::dbBind()</code> to provide protection for SQL
|
||
Injection attacks.</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>sql <span class="ot"><-</span> <span class="fu">glue_sql</span>(<span class="st">"</span></span>
|
||
<span id="cb20-2"><a href="#cb20-2" tabindex="-1"></a><span class="st"> SELECT {`var`}</span></span>
|
||
<span id="cb20-3"><a href="#cb20-3" tabindex="-1"></a><span class="st"> FROM {`tbl`}</span></span>
|
||
<span id="cb20-4"><a href="#cb20-4" tabindex="-1"></a><span class="st"> WHERE {`tbl`}.sepal_length > ?</span></span>
|
||
<span id="cb20-5"><a href="#cb20-5" tabindex="-1"></a><span class="st">"</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb20-6"><a href="#cb20-6" tabindex="-1"></a>query <span class="ot"><-</span> DBI<span class="sc">::</span><span class="fu">dbSendQuery</span>(con, sql)</span>
|
||
<span id="cb20-7"><a href="#cb20-7" tabindex="-1"></a>DBI<span class="sc">::</span><span class="fu">dbBind</span>(query, <span class="fu">list</span>(num))</span>
|
||
<span id="cb20-8"><a href="#cb20-8" tabindex="-1"></a>DBI<span class="sc">::</span><span class="fu">dbFetch</span>(query, <span class="at">n =</span> <span class="dv">4</span>)</span>
|
||
<span id="cb20-9"><a href="#cb20-9" tabindex="-1"></a><span class="co">#> sepal_width</span></span>
|
||
<span id="cb20-10"><a href="#cb20-10" tabindex="-1"></a><span class="co">#> 1 3.5</span></span>
|
||
<span id="cb20-11"><a href="#cb20-11" tabindex="-1"></a><span class="co">#> 2 3.0</span></span>
|
||
<span id="cb20-12"><a href="#cb20-12" tabindex="-1"></a><span class="co">#> 3 3.2</span></span>
|
||
<span id="cb20-13"><a href="#cb20-13" tabindex="-1"></a><span class="co">#> 4 3.1</span></span>
|
||
<span id="cb20-14"><a href="#cb20-14" tabindex="-1"></a>DBI<span class="sc">::</span><span class="fu">dbClearResult</span>(query)</span></code></pre></div>
|
||
<p><code>glue_sql()</code> can be used to build up more complex queries
|
||
with interchangeable sub queries. It returns <code>DBI::SQL()</code>
|
||
objects which are properly protected from quoting.</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>sub_query <span class="ot"><-</span> <span class="fu">glue_sql</span>(<span class="st">"</span></span>
|
||
<span id="cb21-2"><a href="#cb21-2" tabindex="-1"></a><span class="st"> SELECT *</span></span>
|
||
<span id="cb21-3"><a href="#cb21-3" tabindex="-1"></a><span class="st"> FROM {`tbl`}</span></span>
|
||
<span id="cb21-4"><a href="#cb21-4" tabindex="-1"></a><span class="st"> "</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb21-5"><a href="#cb21-5" tabindex="-1"></a></span>
|
||
<span id="cb21-6"><a href="#cb21-6" tabindex="-1"></a><span class="fu">glue_sql</span>(<span class="st">"</span></span>
|
||
<span id="cb21-7"><a href="#cb21-7" tabindex="-1"></a><span class="st"> SELECT s.{`var`}</span></span>
|
||
<span id="cb21-8"><a href="#cb21-8" tabindex="-1"></a><span class="st"> FROM ({sub_query}) AS s</span></span>
|
||
<span id="cb21-9"><a href="#cb21-9" tabindex="-1"></a><span class="st"> "</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb21-10"><a href="#cb21-10" tabindex="-1"></a><span class="co">#> <SQL> SELECT s.`sepal_width`</span></span>
|
||
<span id="cb21-11"><a href="#cb21-11" tabindex="-1"></a><span class="co">#> FROM (SELECT *</span></span>
|
||
<span id="cb21-12"><a href="#cb21-12" tabindex="-1"></a><span class="co">#> FROM `iris`) AS s</span></span></code></pre></div>
|
||
<p>If you want to input multiple values for use in SQL IN statements put
|
||
<code>*</code> at the end of the value and the values will be collapsed
|
||
and quoted appropriately.</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><span class="fu">glue_sql</span>(<span class="st">"SELECT * FROM {`tbl`} WHERE sepal_length IN ({vals*})"</span>,</span>
|
||
<span id="cb22-2"><a href="#cb22-2" tabindex="-1"></a> <span class="at">vals =</span> <span class="dv">1</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb22-3"><a href="#cb22-3" tabindex="-1"></a><span class="co">#> <SQL> SELECT * FROM `iris` WHERE sepal_length IN (1)</span></span>
|
||
<span id="cb22-4"><a href="#cb22-4" tabindex="-1"></a></span>
|
||
<span id="cb22-5"><a href="#cb22-5" tabindex="-1"></a><span class="fu">glue_sql</span>(<span class="st">"SELECT * FROM {`tbl`} WHERE sepal_length IN ({vals*})"</span>,</span>
|
||
<span id="cb22-6"><a href="#cb22-6" tabindex="-1"></a> <span class="at">vals =</span> <span class="dv">1</span><span class="sc">:</span><span class="dv">5</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb22-7"><a href="#cb22-7" tabindex="-1"></a><span class="co">#> <SQL> SELECT * FROM `iris` WHERE sepal_length IN (1, 2, 3, 4, 5)</span></span>
|
||
<span id="cb22-8"><a href="#cb22-8" tabindex="-1"></a></span>
|
||
<span id="cb22-9"><a href="#cb22-9" tabindex="-1"></a><span class="fu">glue_sql</span>(<span class="st">"SELECT * FROM {`tbl`} WHERE species IN ({vals*})"</span>,</span>
|
||
<span id="cb22-10"><a href="#cb22-10" tabindex="-1"></a> <span class="at">vals =</span> <span class="st">"setosa"</span>, <span class="at">.con =</span> con)</span>
|
||
<span id="cb22-11"><a href="#cb22-11" tabindex="-1"></a><span class="co">#> <SQL> SELECT * FROM `iris` WHERE species IN ('setosa')</span></span>
|
||
<span id="cb22-12"><a href="#cb22-12" tabindex="-1"></a></span>
|
||
<span id="cb22-13"><a href="#cb22-13" tabindex="-1"></a><span class="fu">glue_sql</span>(<span class="st">"SELECT * FROM {`tbl`} WHERE species IN ({vals*})"</span>,</span>
|
||
<span id="cb22-14"><a href="#cb22-14" tabindex="-1"></a> <span class="at">vals =</span> <span class="fu">c</span>(<span class="st">"setosa"</span>, <span class="st">"versicolor"</span>), <span class="at">.con =</span> con)</span>
|
||
<span id="cb22-15"><a href="#cb22-15" tabindex="-1"></a><span class="co">#> <SQL> SELECT * FROM `iris` WHERE species IN ('setosa', 'versicolor')</span></span></code></pre></div>
|
||
</div>
|
||
|
||
|
||
|
||
<!-- code folding -->
|
||
|
||
|
||
<!-- dynamically load mathjax for compatibility with self-contained -->
|
||
<script>
|
||
(function () {
|
||
var script = document.createElement("script");
|
||
script.type = "text/javascript";
|
||
script.src = "https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML";
|
||
document.getElementsByTagName("head")[0].appendChild(script);
|
||
})();
|
||
</script>
|
||
|
||
</body>
|
||
</html>
|