EVOLUTION-MANAGER
Edit File: transformers.html
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This allows you to write things like <code>glue_sql()</code>, which automatically quotes variables for you or add a syntax for automatically collapsing outputs.</p> <p>The transformer functions simply take two arguments <code>text</code> and <code>envir</code>, where <code>text</code> is the unparsed string inside the glue block and <code>envir</code> is the execution environment. Most transformers will then call <code>eval(parse(text = text, keep.source = FALSE), envir)</code> which parses and evaluates the code.</p> <p>You can then supply the transformer function to glue with the <code>.transformer</code> argument. In this way users can manipulate the text before parsing and change the output after evaluation.</p> <p>It is often useful to write a <code>glue()</code> wrapper function which supplies a <code>.transformer</code> to <code>glue()</code> or <code>glue_data()</code> and potentially has additional arguments. One important consideration when doing this is to include <code>.envir = parent.frame()</code> in the wrapper to ensure the evaluation environment is correct.</p> <p>Some example implementations of potentially useful transformers follow. The aim right now is not to include most of these custom functions within the <code>glue</code> package. Rather, users are encouraged to create custom functions using transformers to fit their individual needs.</p> <div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1"></a><span class="kw">library</span>(glue)</span></code></pre></div> <div id="collapse-transformer" class="section level3"> <h3>collapse transformer</h3> <p>A transformer which automatically collapses any glue block ending with <code>*</code>.</p> <div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb2-1"><a href="#cb2-1"></a>collapse_transformer <-<span class="st"> </span><span class="cf">function</span>(<span class="dt">regex =</span> <span class="st">"[*]$"</span>, ...) {</span> <span id="cb2-2"><a href="#cb2-2"></a> <span class="cf">function</span>(text, envir) {</span> <span id="cb2-3"><a href="#cb2-3"></a> collapse <-<span class="st"> </span><span class="kw">grepl</span>(regex, text)</span> <span id="cb2-4"><a href="#cb2-4"></a> <span class="cf">if</span> (collapse) {</span> <span id="cb2-5"><a href="#cb2-5"></a> text <-<span class="st"> </span><span class="kw">sub</span>(regex, <span class="st">""</span>, text)</span> <span id="cb2-6"><a href="#cb2-6"></a> }</span> <span id="cb2-7"><a href="#cb2-7"></a> res <-<span class="st"> </span><span class="kw">identity_transformer</span>(text, envir)</span> <span id="cb2-8"><a href="#cb2-8"></a> <span class="cf">if</span> (collapse) {</span> <span id="cb2-9"><a href="#cb2-9"></a> <span class="kw">glue_collapse</span>(res, ...) </span> <span id="cb2-10"><a href="#cb2-10"></a> } <span class="cf">else</span> {</span> <span id="cb2-11"><a href="#cb2-11"></a> res</span> <span id="cb2-12"><a href="#cb2-12"></a> }</span> <span id="cb2-13"><a href="#cb2-13"></a> }</span> <span id="cb2-14"><a href="#cb2-14"></a>}</span> <span id="cb2-15"><a href="#cb2-15"></a></span> <span id="cb2-16"><a href="#cb2-16"></a><span class="kw">glue</span>(<span class="st">"{1:5*}</span><span class="ch">\n</span><span class="st">{letters[1:5]*}"</span>, <span class="dt">.transformer =</span> <span class="kw">collapse_transformer</span>(<span class="dt">sep =</span> <span class="st">", "</span>))</span> <span id="cb2-17"><a href="#cb2-17"></a><span class="co">#> 1, 2, 3, 4, 5</span></span> <span id="cb2-18"><a href="#cb2-18"></a><span class="co">#> a, b, c, d, e</span></span> <span id="cb2-19"><a href="#cb2-19"></a></span> <span id="cb2-20"><a href="#cb2-20"></a><span class="kw">glue</span>(<span class="st">"{1:5*}</span><span class="ch">\n</span><span class="st">{letters[1:5]*}"</span>, <span class="dt">.transformer =</span> <span class="kw">collapse_transformer</span>(<span class="dt">sep =</span> <span class="st">", "</span>, <span class="dt">last =</span> <span class="st">" and "</span>))</span> <span id="cb2-21"><a href="#cb2-21"></a><span class="co">#> 1, 2, 3, 4 and 5</span></span> <span id="cb2-22"><a href="#cb2-22"></a><span class="co">#> a, b, c, d and e</span></span> <span id="cb2-23"><a href="#cb2-23"></a></span> <span id="cb2-24"><a href="#cb2-24"></a>x <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"one"</span>, <span class="st">"two"</span>)</span> <span id="cb2-25"><a href="#cb2-25"></a><span class="kw">glue</span>(<span class="st">"{x}: {1:5*}"</span>, <span class="dt">.transformer =</span> <span class="kw">collapse_transformer</span>(<span class="dt">sep =</span> <span class="st">", "</span>))</span> <span id="cb2-26"><a href="#cb2-26"></a><span class="co">#> one: 1, 2, 3, 4, 5</span></span> <span id="cb2-27"><a href="#cb2-27"></a><span class="co">#> two: 1, 2, 3, 4, 5</span></span></code></pre></div> </div> <div id="shell-quoting-transformer" class="section level3"> <h3>Shell quoting transformer</h3> <p>A transformer which automatically quotes variables for use in shell commands, e.g. via <code>system()</code> or <code>system2()</code>.</p> <div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1"></a>shell_transformer <-<span class="st"> </span><span class="cf">function</span>(<span class="dt">type =</span> <span class="kw">c</span>(<span class="st">"sh"</span>, <span class="st">"csh"</span>, <span class="st">"cmd"</span>, <span class="st">"cmd2"</span>)) {</span> <span id="cb3-2"><a href="#cb3-2"></a> type <-<span class="st"> </span><span class="kw">match.arg</span>(type)</span> <span id="cb3-3"><a href="#cb3-3"></a> <span class="cf">function</span>(text, envir) {</span> <span id="cb3-4"><a href="#cb3-4"></a> res <-<span class="st"> </span><span class="kw">eval</span>(<span class="kw">parse</span>(<span class="dt">text =</span> text, <span class="dt">keep.source =</span> <span class="ot">FALSE</span>), envir)</span> <span id="cb3-5"><a href="#cb3-5"></a> <span class="kw">shQuote</span>(res)</span> <span id="cb3-6"><a href="#cb3-6"></a> }</span> <span id="cb3-7"><a href="#cb3-7"></a>}</span> <span id="cb3-8"><a href="#cb3-8"></a></span> <span id="cb3-9"><a href="#cb3-9"></a>glue_sh <-<span class="st"> </span><span class="cf">function</span>(..., <span class="dt">.envir =</span> <span class="kw">parent.frame</span>(), <span class="dt">.type =</span> <span class="kw">c</span>(<span class="st">"sh"</span>, <span class="st">"csh"</span>, <span class="st">"cmd"</span>, <span class="st">"cmd2"</span>)) {</span> <span id="cb3-10"><a href="#cb3-10"></a> .type <-<span class="st"> </span><span class="kw">match.arg</span>(.type)</span> <span id="cb3-11"><a href="#cb3-11"></a> <span class="kw">glue</span>(..., <span class="dt">.envir =</span> .envir, <span class="dt">.transformer =</span> <span class="kw">shell_transformer</span>(.type))</span> <span id="cb3-12"><a href="#cb3-12"></a></span> <span id="cb3-13"><a href="#cb3-13"></a>}</span> <span id="cb3-14"><a href="#cb3-14"></a></span> <span id="cb3-15"><a href="#cb3-15"></a>filename <-<span class="st"> "test"</span></span> <span id="cb3-16"><a href="#cb3-16"></a><span class="kw">writeLines</span>(<span class="dt">con =</span> filename, <span class="st">"hello!"</span>)</span> <span id="cb3-17"><a href="#cb3-17"></a></span> <span id="cb3-18"><a href="#cb3-18"></a>command <-<span class="st"> </span><span class="kw">glue_sh</span>(<span class="st">"cat {filename}"</span>)</span> <span id="cb3-19"><a href="#cb3-19"></a>command</span> <span id="cb3-20"><a href="#cb3-20"></a><span class="co">#> cat 'test'</span></span> <span id="cb3-21"><a href="#cb3-21"></a><span class="kw">system</span>(command)</span></code></pre></div> </div> <div id="emoji-transformer" class="section level3"> <h3>emoji transformer</h3> <p>A transformer which converts the text to the equivalent emoji.</p> <div class="sourceCode" id="cb4"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb4-1"><a href="#cb4-1"></a>emoji_transformer <-<span class="st"> </span><span class="cf">function</span>(text, envir) {</span> <span id="cb4-2"><a href="#cb4-2"></a> <span class="cf">if</span> (<span class="kw">grepl</span>(<span class="st">"[*]$"</span>, text)) {</span> <span id="cb4-3"><a href="#cb4-3"></a> text <-<span class="st"> </span><span class="kw">sub</span>(<span class="st">"[*]$"</span>, <span class="st">""</span>, text)</span> <span id="cb4-4"><a href="#cb4-4"></a> <span class="kw">glue_collapse</span>(<span class="kw">ji_find</span>(text)<span class="op">$</span>emoji)</span> <span id="cb4-5"><a href="#cb4-5"></a> } <span class="cf">else</span> {</span> <span id="cb4-6"><a href="#cb4-6"></a> <span class="kw">ji</span>(text)</span> <span id="cb4-7"><a href="#cb4-7"></a> }</span> <span id="cb4-8"><a href="#cb4-8"></a>}</span> <span id="cb4-9"><a href="#cb4-9"></a></span> <span id="cb4-10"><a href="#cb4-10"></a>glue_ji <-<span class="st"> </span><span class="cf">function</span>(..., <span class="dt">.envir =</span> <span class="kw">parent.frame</span>()) {</span> <span id="cb4-11"><a href="#cb4-11"></a> <span class="kw">glue</span>(..., <span class="dt">.open =</span> <span class="st">":"</span>, <span class="dt">.close =</span> <span class="st">":"</span>, <span class="dt">.envir =</span> .envir, <span class="dt">.transformer =</span> emoji_transformer)</span> <span id="cb4-12"><a href="#cb4-12"></a>}</span> <span id="cb4-13"><a href="#cb4-13"></a><span class="kw">glue_ji</span>(<span class="st">"one :heart:"</span>)</span> <span id="cb4-14"><a href="#cb4-14"></a><span class="kw">glue_ji</span>(<span class="st">"many :heart*:"</span>)</span></code></pre></div> </div> <div id="sprintf-transformer" class="section level3"> <h3>sprintf transformer</h3> <p>A transformer which allows succinct sprintf format strings.</p> <div class="sourceCode" id="cb5"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb5-1"><a href="#cb5-1"></a>sprintf_transformer <-<span class="st"> </span><span class="cf">function</span>(text, envir) {</span> <span id="cb5-2"><a href="#cb5-2"></a> m <-<span class="st"> </span><span class="kw">regexpr</span>(<span class="st">":.+$"</span>, text)</span> <span id="cb5-3"><a href="#cb5-3"></a> <span class="cf">if</span> (m <span class="op">!=</span><span class="st"> </span><span class="dv">-1</span>) {</span> <span id="cb5-4"><a href="#cb5-4"></a> format <-<span class="st"> </span><span class="kw">substring</span>(<span class="kw">regmatches</span>(text, m), <span class="dv">2</span>)</span> <span id="cb5-5"><a href="#cb5-5"></a> <span class="kw">regmatches</span>(text, m) <-<span class="st"> ""</span></span> <span id="cb5-6"><a href="#cb5-6"></a> res <-<span class="st"> </span><span class="kw">eval</span>(<span class="kw">parse</span>(<span class="dt">text =</span> text, <span class="dt">keep.source =</span> <span class="ot">FALSE</span>), envir)</span> <span id="cb5-7"><a href="#cb5-7"></a> <span class="kw">do.call</span>(sprintf, <span class="kw">list</span>(<span class="kw">glue</span>(<span class="st">"%{format}f"</span>), res))</span> <span id="cb5-8"><a href="#cb5-8"></a> } <span class="cf">else</span> {</span> <span id="cb5-9"><a href="#cb5-9"></a> <span class="kw">eval</span>(<span class="kw">parse</span>(<span class="dt">text =</span> text, <span class="dt">keep.source =</span> <span class="ot">FALSE</span>), envir)</span> <span id="cb5-10"><a href="#cb5-10"></a> }</span> <span id="cb5-11"><a href="#cb5-11"></a>}</span> <span id="cb5-12"><a href="#cb5-12"></a></span> <span id="cb5-13"><a href="#cb5-13"></a>glue_fmt <-<span class="st"> </span><span class="cf">function</span>(..., <span class="dt">.envir =</span> <span class="kw">parent.frame</span>()) {</span> <span id="cb5-14"><a href="#cb5-14"></a> <span class="kw">glue</span>(..., <span class="dt">.transformer =</span> sprintf_transformer, <span class="dt">.envir =</span> .envir)</span> <span id="cb5-15"><a href="#cb5-15"></a>}</span> <span id="cb5-16"><a href="#cb5-16"></a><span class="kw">glue_fmt</span>(<span class="st">"π = {pi:.2}"</span>)</span> <span id="cb5-17"><a href="#cb5-17"></a><span class="co">#> π = 3.14</span></span></code></pre></div> </div> <div id="safely-transformer" class="section level3"> <h3>safely transformer</h3> <p>A transformer that acts like <code>purrr::safely()</code>, which returns a value instead of an error.</p> <div class="sourceCode" id="cb6"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb6-1"><a href="#cb6-1"></a>safely_transformer <-<span class="st"> </span><span class="cf">function</span>(<span class="dt">otherwise =</span> <span class="ot">NA</span>) {</span> <span id="cb6-2"><a href="#cb6-2"></a> <span class="cf">function</span>(text, envir) {</span> <span id="cb6-3"><a href="#cb6-3"></a> <span class="kw">tryCatch</span>(</span> <span id="cb6-4"><a href="#cb6-4"></a> <span class="kw">eval</span>(<span class="kw">parse</span>(<span class="dt">text =</span> text, <span class="dt">keep.source =</span> <span class="ot">FALSE</span>), envir),</span> <span id="cb6-5"><a href="#cb6-5"></a> <span class="dt">error =</span> <span class="cf">function</span>(e) <span class="cf">if</span> (<span class="kw">is.language</span>(otherwise)) <span class="kw">eval</span>(otherwise) <span class="cf">else</span> otherwise)</span> <span id="cb6-6"><a href="#cb6-6"></a> }</span> <span id="cb6-7"><a href="#cb6-7"></a>}</span> <span id="cb6-8"><a href="#cb6-8"></a></span> <span id="cb6-9"><a href="#cb6-9"></a>glue_safely <-<span class="st"> </span><span class="cf">function</span>(..., <span class="dt">.otherwise =</span> <span class="ot">NA</span>, <span class="dt">.envir =</span> <span class="kw">parent.frame</span>()) {</span> <span id="cb6-10"><a href="#cb6-10"></a> <span class="kw">glue</span>(..., <span class="dt">.transformer =</span> <span class="kw">safely_transformer</span>(.otherwise), <span class="dt">.envir =</span> .envir)</span> <span id="cb6-11"><a href="#cb6-11"></a>}</span> <span id="cb6-12"><a href="#cb6-12"></a></span> <span id="cb6-13"><a href="#cb6-13"></a><span class="co"># Default returns missing if there is an error</span></span> <span id="cb6-14"><a href="#cb6-14"></a><span class="kw">glue_safely</span>(<span class="st">"foo: {xyz}"</span>)</span> <span id="cb6-15"><a href="#cb6-15"></a><span class="co">#> foo: NA</span></span> <span id="cb6-16"><a href="#cb6-16"></a></span> <span id="cb6-17"><a href="#cb6-17"></a><span class="co"># Or an empty string</span></span> <span id="cb6-18"><a href="#cb6-18"></a><span class="kw">glue_safely</span>(<span class="st">"foo: {xyz}"</span>, <span class="dt">.otherwise =</span> <span class="st">"Error"</span>)</span> <span id="cb6-19"><a href="#cb6-19"></a><span class="co">#> foo: Error</span></span> <span id="cb6-20"><a href="#cb6-20"></a></span> <span id="cb6-21"><a href="#cb6-21"></a><span class="co"># Or output the error message in red</span></span> <span id="cb6-22"><a href="#cb6-22"></a><span class="kw">library</span>(crayon)</span> <span id="cb6-23"><a href="#cb6-23"></a><span class="kw">glue_safely</span>(<span class="st">"foo: {xyz}"</span>, <span class="dt">.otherwise =</span> <span class="kw">quote</span>(<span class="kw">glue</span>(<span class="st">"{red}Error: {conditionMessage(e)}{reset}"</span>)))</span> <span id="cb6-24"><a href="#cb6-24"></a><span class="co">#> foo: Error: object 'xyz' not found</span></span></code></pre></div> </div> <div id="variables-and-values-transformer" class="section level3"> <h3>“Variables and Values” transformer</h3> <p>A transformer that expands input of the form <code>{var_name=}</code> into <code>var_name = var_value</code>, i.e. a shorthand for exposing variable names with their values. This is inspired by an <a href="https://docs.python.org/3.8/whatsnew/3.8.html#f-strings-now-support-for-quick-and-easy-debugging">f-strings feature coming in Python 3.8</a>. It’s actually more general: you can use it with an expression input such as <code>{expr=}</code>.</p> <div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1"></a>vv_transformer <-<span class="st"> </span><span class="cf">function</span>(text, envir) {</span> <span id="cb7-2"><a href="#cb7-2"></a> regex <-<span class="st"> "=$"</span></span> <span id="cb7-3"><a href="#cb7-3"></a> <span class="cf">if</span> (<span class="op">!</span><span class="kw">grepl</span>(regex, text)) {</span> <span id="cb7-4"><a href="#cb7-4"></a> <span class="kw">return</span>(<span class="kw">identity_transformer</span>(text, envir))</span> <span id="cb7-5"><a href="#cb7-5"></a> }</span> <span id="cb7-6"><a href="#cb7-6"></a></span> <span id="cb7-7"><a href="#cb7-7"></a> text <-<span class="st"> </span><span class="kw">sub</span>(regex, <span class="st">""</span>, text)</span> <span id="cb7-8"><a href="#cb7-8"></a> res <-<span class="st"> </span><span class="kw">identity_transformer</span>(text, envir)</span> <span id="cb7-9"><a href="#cb7-9"></a> n <-<span class="st"> </span><span class="kw">length</span>(res)</span> <span id="cb7-10"><a href="#cb7-10"></a> res <-<span class="st"> </span><span class="kw">glue_collapse</span>(res, <span class="dt">sep =</span> <span class="st">", "</span>)</span> <span id="cb7-11"><a href="#cb7-11"></a> <span class="cf">if</span> (n <span class="op">></span><span class="st"> </span><span class="dv">1</span>) {</span> <span id="cb7-12"><a href="#cb7-12"></a> res <-<span class="st"> </span><span class="kw">c</span>(<span class="st">"["</span>, res, <span class="st">"]"</span>)</span> <span id="cb7-13"><a href="#cb7-13"></a> }</span> <span id="cb7-14"><a href="#cb7-14"></a> <span class="kw">glue_collapse</span>(<span class="kw">c</span>(text, <span class="st">" = "</span>, res))</span> <span id="cb7-15"><a href="#cb7-15"></a>}</span></code></pre></div> <div class="sourceCode" id="cb8"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb8-1"><a href="#cb8-1"></a><span class="kw">set.seed</span>(<span class="dv">1234</span>)</span> <span id="cb8-2"><a href="#cb8-2"></a>description <-<span class="st"> "some random"</span></span> <span id="cb8-3"><a href="#cb8-3"></a>numbers <-<span class="st"> </span><span class="kw">sample</span>(<span class="dv">100</span>, <span class="dv">4</span>)</span> <span id="cb8-4"><a href="#cb8-4"></a>average <-<span class="st"> </span><span class="kw">mean</span>(numbers)</span> <span id="cb8-5"><a href="#cb8-5"></a>sum <-<span class="st"> </span><span class="kw">sum</span>(numbers)</span> <span id="cb8-6"><a href="#cb8-6"></a></span> <span id="cb8-7"><a href="#cb8-7"></a><span class="kw">glue</span>(<span class="st">"For {description} {numbers=}, {average=}, {sum=}."</span>, <span class="dt">.transformer =</span> vv_transformer)</span> <span id="cb8-8"><a href="#cb8-8"></a><span class="co">#> For some random numbers = [28, 80, 22, 9], average = 34.75, sum = 139.</span></span> <span id="cb8-9"><a href="#cb8-9"></a></span> <span id="cb8-10"><a href="#cb8-10"></a>a <-<span class="st"> </span><span class="dv">3</span></span> <span id="cb8-11"><a href="#cb8-11"></a>b <-<span class="st"> </span><span class="fl">5.6</span></span> <span id="cb8-12"><a href="#cb8-12"></a><span class="kw">glue</span>(<span class="st">"{a=}</span><span class="ch">\n</span><span class="st">{b=}</span><span class="ch">\n</span><span class="st">{a * 9 + b * 2=}"</span>, <span class="dt">.transformer =</span> vv_transformer)</span> <span id="cb8-13"><a href="#cb8-13"></a><span class="co">#> a = 3</span></span> <span id="cb8-14"><a href="#cb8-14"></a><span class="co">#> b = 5.6</span></span> <span id="cb8-15"><a href="#cb8-15"></a><span class="co">#> a * 9 + b * 2 = 38.2</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>