skimr

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For example, a data frame is printed like this<a href="#fn1" class="footnote-ref" id="fnref1">1</a>: <div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb1-1" tabindex="-1"></a>head(mtcars)</code></pre></div> <pre><code> mpg cyl disp hp drat wt qsec vs am gear carb Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1</code></pre> The text representation of the data frame above may look very familiar with most R users, but for reporting purposes, it may not be satisfactory – often times we want to see a table representation instead. That is the problem that the chunk option <code>render</code> and the S3 generic function <code>knit_print()</code> try to solve. <div id="customize-printing" class="section level2"> <h2>Customize Printing</h2> After we evaluate each R expression in a code chunk, there is an object returned. For example, <code>1 + 1</code> returns <code>2</code>. This object is passed to the chunk option <code>render</code>, which is a function with two arguments, <code>x</code> and <code>options</code>, or <code>x</code> and <code>...</code>. The default value for the <code>render</code> option is <code>knit_print</code>, an S3 function in knitr: <div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb3-1" tabindex="-1"></a>library(knitr) <a href="#cb3-2" tabindex="-1"></a>knit_print # an S3 generic function</code></pre></div> <pre><code>## function (x, ...) ## { ## if (need_screenshot(x, ...)) { ## html_screenshot(x) ## } ## else { ## UseMethod("knit_print") ## } ## } ## <bytecode: 0x11ba3fe70> ## <environment: namespace:knitr></code></pre> <div class="sourceCode" id="cb5"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb5-1" tabindex="-1"></a>methods(knit_print)</code></pre></div> <pre><code>## [1] knit_print.css* knit_print.data.frame* ## [3] knit_print.default* knit_print.grouped_df* ## [5] knit_print.html* knit_print.html_dependency* ## [7] knit_print.knit_asis* knit_print.knit_asis_url* ## [9] knit_print.knitr_kable* knit_print.output_format_dependency* ## [11] knit_print.rowwise_df* knit_print.sass* ## [13] knit_print.shiny.tag* knit_print.shiny.tag.list* ## [15] knit_print.tbl_sql* ## see '?methods' for accessing help and source code</code></pre> <div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb7-1" tabindex="-1"></a>getS3method('knit_print', 'default') # the default method</code></pre></div> <pre><code>## function (x, ..., inline = FALSE) ## { ## if (inline) ## x ## else normal_print(x) ## } ## <bytecode: 0x12bf8dbc8> ## <environment: namespace:knitr></code></pre> <div class="sourceCode" id="cb9"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb9-1" tabindex="-1"></a>normal_print</code></pre></div> <pre><code>## function (x, ...) ## if (isS4(x)) methods::show(x) else print(x) ## <bytecode: 0x11bdd4bc0> ## <environment: namespace:evaluate></code></pre> As we can see, <code>knit_print()</code> has a <code>default</code> method, which is basically <code>print()</code> or <code>show()</code>, depending on whether the object is an S4 object. This means it does nothing special when printing R objects: <div class="sourceCode" id="cb11"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb11-1" tabindex="-1"></a>knit_print(1:10) <a href="#cb11-2" tabindex="-1"></a>## [1] 1 2 3 4 5 6 7 8 9 10 <a href="#cb11-3" tabindex="-1"></a>knit_print(head(mtcars)) <a href="#cb11-4" tabindex="-1"></a>## mpg cyl disp hp drat wt qsec vs am gear carb <a href="#cb11-5" tabindex="-1"></a>## Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 <a href="#cb11-6" tabindex="-1"></a>## Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 <a href="#cb11-7" tabindex="-1"></a>## Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 <a href="#cb11-8" tabindex="-1"></a>## Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 <a href="#cb11-9" tabindex="-1"></a>## Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 <a href="#cb11-10" tabindex="-1"></a>## Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1</code></pre></div> S3 generic functions are extensible in the sense that we can define custom methods for them. A method <code>knit_print.foo()</code> will be applied to the object that has the class <code>foo</code>. Here is quick example of how we can print data frames as tables: <div class="sourceCode" id="cb12"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb12-1" tabindex="-1"></a>library(knitr) <a href="#cb12-2" tabindex="-1"></a># define a method for objects of the class data.frame <a href="#cb12-3" tabindex="-1"></a>knit_print.data.frame = function(x, ...) { <a href="#cb12-4" tabindex="-1"></a> res = paste(c('', '', kable(x)), collapse = '\n') <a href="#cb12-5" tabindex="-1"></a> asis_output(res) <a href="#cb12-6" tabindex="-1"></a>} <a href="#cb12-7" tabindex="-1"></a># register the method <a href="#cb12-8" tabindex="-1"></a>registerS3method("knit_print", "data.frame", knit_print.data.frame)</code></pre></div> If you define a method in a code chunk in a knitr document, the call to <code>registerS3method()</code> will be necessary for R >= 3.5.0, because the S3 dispatch mechanism has changed since R 3.5.0. If you are developing an R package, see the section <a href="#for-package-authors">For package authors</a> below. We expect the print method to return a character vector, or an object that can be coerced into a character vector. In the example above, the <code>kable()</code> function returns a character vector, which we pass to the <code>asis_output()</code> function so that later knitr knows that this result needs no special treatment (just write it as is), otherwise it depends on the chunk option <code>results</code> (<code>= 'asis'</code> / <code>'markup'</code> / <code>'hide'</code>) how a normal character vector should be written. The function <code>asis_output()</code> has the same effect as <code>results = 'asis'</code>, but saves us the effort to provide this chunk option explicitly. Now we check how the printing behavior is changed. We print a number, a character vector, a list, a data frame, and write a character value using <code>cat()</code> in the chunk below: <div class="sourceCode" id="cb13"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb13-1" tabindex="-1"></a>1 + 1</code></pre></div> <pre><code>## [1] 2</code></pre> <div class="sourceCode" id="cb15"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb15-1" tabindex="-1"></a>head(letters)</code></pre></div> <pre><code>## [1] "a" "b" "c" "d" "e" "f"</code></pre> <div class="sourceCode" id="cb17"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb17-1" tabindex="-1"></a>list(a = 1, b = 9:4)</code></pre></div> <pre><code>## $a ## [1] 1 ## ## $b ## [1] 9 8 7 6 5 4</code></pre> <div class="sourceCode" id="cb19"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb19-1" tabindex="-1"></a>head(mtcars)</code></pre></div> <table style="width:100%;"> <colgroup> <col width="26%" /> <col width="7%" /> <col width="5%" /> <col width="7%" /> <col width="5%" /> <col width="7%" /> <col width="8%" /> <col width="8%" /> <col width="4%" /> <col width="4%" /> <col width="7%" /> <col width="7%" /> </colgroup> <thead> <tr class="header"> <th align="left"></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">21.0</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">21.0</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">22.8</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">21.4</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">18.7</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> <tr class="even"> <td align="left">Valiant</td> <td align="right">18.1</td> <td align="right">6</td> <td align="right">225</td> <td align="right">105</td> <td align="right">2.76</td> <td align="right">3.460</td> <td align="right">20.22</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 class="sourceCode" id="cb20"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb20-1" tabindex="-1"></a>cat('This is cool.')</code></pre></div> <pre><code>## This is cool.</code></pre> We see all objects except the data frame were printed “normally”<a href="#fn2" class="footnote-ref" id="fnref2">2</a>. The data frame was printed as a real table. Note you do not have to use <code>kable()</code> to create tables – there are many other options such as xtable. Just make sure the print method returns a character string. The <a href="https://github.com/yihui/printr">printr</a> package is a companion to knitr containing printing methods for some common objects like matrices and data frames. Users only need to load this package to get attractive printed results. A major factor to consider (which has been considered in printr) when defining a printing method is the output format. For example, the table syntax can be entirely different when the output is LaTeX vs when it is Markdown. It is strongly recommended that your S3 method has a <code>...</code> argument, so that your method can safely ignore arguments that are passed to <code>knit_print()</code> but not defined in your method. At the moment, a <code>knit_print()</code> method can have two optional arguments: <ul> <li>the <code>options</code> argument takes a list of the current chunk options;</li> <li>the <code>inline</code> argument indicates if the method is called in code chunks or inline R code;</li> </ul> Depending on your application, you may optionally use these arguments. Here are some examples: <div class="sourceCode" id="cb22"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb22-1" tabindex="-1"></a>knit_print.classA = function(x, ...) { <a href="#cb22-2" tabindex="-1"></a> # ignore options and inline <a href="#cb22-3" tabindex="-1"></a>} <a href="#cb22-4" tabindex="-1"></a>knit_print.classB = function(x, options, ...) { <a href="#cb22-5" tabindex="-1"></a> # use the chunk option out.height <a href="#cb22-6" tabindex="-1"></a> asis_output(paste0( <a href="#cb22-7" tabindex="-1"></a> '<iframe src="https://yihui.org" height="', options$out.height, '"></iframe>', <a href="#cb22-8" tabindex="-1"></a> )) <a href="#cb22-9" tabindex="-1"></a>} <a href="#cb22-10" tabindex="-1"></a>knit_print.classC = function(x, inline = FALSE, ...) { <a href="#cb22-11" tabindex="-1"></a> # different output according to inline=TRUE/FALSE <a href="#cb22-12" tabindex="-1"></a> if (inline) { <a href="#cb22-13" tabindex="-1"></a> 'inline output for classC' <a href="#cb22-14" tabindex="-1"></a> } else { <a href="#cb22-15" tabindex="-1"></a> 'chunk output for classC' <a href="#cb22-16" tabindex="-1"></a> } <a href="#cb22-17" tabindex="-1"></a>} <a href="#cb22-18" tabindex="-1"></a>knit_print.classD = function(x, options, inline = FALSE, ...) { <a href="#cb22-19" tabindex="-1"></a> # use both options and inline <a href="#cb22-20" tabindex="-1"></a>}</code></pre></div> Note that when using your (or another) <code>knit_print()</code> method inline (if it supports that), you must not call <code>knit_print()</code> on the object, but just have it return. For example, your inline code should read <code>`r c("foo")`</code> and not <code>`r knit_print(c("foo"))`</code>. The latter inline code would yield the methods’ result for in-chunk (not inline), because, as set up in the above, <code>knit_print()</code> methods default to <code>inline = FALSE</code>. This default gets overwritten depending on the context in which <code>knit_print()</code> is called (inline or in-chunk), only when <code>knit_print()</code> is called by knitr (not you) via the <code>render</code> option (see below). You can, of course, always manually set the inline option <code>`r knit_print(c("foo"), inline = TRUE)`</code>, but that’s a lot of typing. </div> <div id="a-low-level-explanation" class="section level2"> <h2>A Low-level Explanation</h2> You can skip this section if you do not care about the low-level implementation details. <div id="the-render-option" class="section level3"> <h3>The <code>render</code> option</h3> As mentioned before, the chunk option <code>render</code> is a function that defaults to <code>knit_print()</code>. We can certainly use other render functions. For example, we create a dummy function that always says “I do not know what to print” no matter what objects it receives: <div class="sourceCode" id="cb23"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb23-1" tabindex="-1"></a>dummy_print = function(x, ...) { <a href="#cb23-2" tabindex="-1"></a> cat("I do not know what to print!") <a href="#cb23-3" tabindex="-1"></a> # this function implicitly returns an invisible NULL <a href="#cb23-4" tabindex="-1"></a>}</code></pre></div> Now we use the chunk option <code>render = dummy_print</code>: <div class="sourceCode" id="cb24"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb24-1" tabindex="-1"></a>1 + 1 <a href="#cb24-2" tabindex="-1"></a>## I do not know what to print! <a href="#cb24-3" tabindex="-1"></a>head(letters) <a href="#cb24-4" tabindex="-1"></a>## I do not know what to print! <a href="#cb24-5" tabindex="-1"></a>list(a = 1, b = 9:4) <a href="#cb24-6" tabindex="-1"></a>## I do not know what to print! <a href="#cb24-7" tabindex="-1"></a>head(mtcars) <a href="#cb24-8" tabindex="-1"></a>## I do not know what to print! <a href="#cb24-9" tabindex="-1"></a>cat('This is cool.') <a href="#cb24-10" tabindex="-1"></a>## This is cool.</code></pre></div> Note the <code>render</code> function is only applied to visible objects. There are cases in which the objects returned are invisible, e.g. those wrapped in <code>invisible()</code>. <div class="sourceCode" id="cb25"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb25-1" tabindex="-1"></a>1 + 1</code></pre></div> <pre><code>## [1] 2</code></pre> <div class="sourceCode" id="cb27"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb27-1" tabindex="-1"></a>invisible(1 + 1) <a href="#cb27-2" tabindex="-1"></a>invisible(head(mtcars)) <a href="#cb27-3" tabindex="-1"></a>x = 1:10 # invisibly returns 1:10</code></pre></div> </div> <div id="metadata" class="section level3"> <h3>Metadata</h3> The print function can have a side effect of passing “metadata” about objects to knitr, and knitr will collect this information as it prints objects. The motivation of collecting metadata is to store external dependencies of the objects to be printed. Normally we print an object only to obtain a text representation, but there are cases that can be more complicated. For example, a <a href="https://ggvis.rstudio.com/">ggvis</a> graph requires external JavaScript and CSS dependencies such as <code>ggvis.js</code>. The graph itself is basically a fragment of JavaScript code, which will not work unless the required libraries are loaded (in the HTML header). Therefore we need to collect the dependencies of an object beside printing the object itself. One way to specify the dependencies is through the <code>meta</code> argument of <code>asis_output()</code>. Here is a pseudo example: <div class="sourceCode" id="cb28"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb28-1" tabindex="-1"></a># pseudo code <a href="#cb28-2" tabindex="-1"></a>knit_print.ggvis = function(x, ...) { <a href="#cb28-3" tabindex="-1"></a> res = ggvis::print_this_object(x) <a href="#cb28-4" tabindex="-1"></a> knitr::asis_output(res, meta = list( <a href="#cb28-5" tabindex="-1"></a> ggvis = list( <a href="#cb28-6" tabindex="-1"></a> version = '0.1.0', <a href="#cb28-7" tabindex="-1"></a> js = system.file('www', 'js', 'ggvis.js', package = 'ggvis'), <a href="#cb28-8" tabindex="-1"></a> css = system.file('www', 'www', 'ggvis.css', package = 'ggvis') <a href="#cb28-9" tabindex="-1"></a> ) <a href="#cb28-10" tabindex="-1"></a> )) <a href="#cb28-11" tabindex="-1"></a>}</code></pre></div> Then when knitr prints a ggvis object, the <code>meta</code> information will be collected and stored. After knitting is done, we can obtain a list of all the dependencies via <code>knit_meta()</code>. It is very likely that there are duplicate entries in the list, and it is up to the package authors to clean them up, and process the metadata list in their own way (e.g. write the dependencies into the HTML header). We give a few more quick and dirty examples below to see how <code>knit_meta()</code> works. Now we define a print method for <code>foo</code> objects: <div class="sourceCode" id="cb29"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb29-1" tabindex="-1"></a>library(knitr) <a href="#cb29-2" tabindex="-1"></a>knit_print.foo = function(x, ...) { <a href="#cb29-3" tabindex="-1"></a> res = paste('> **This is a `foo` object**:', x) <a href="#cb29-4" tabindex="-1"></a> asis_output(res, meta = list( <a href="#cb29-5" tabindex="-1"></a> js = system.file('www', 'shared', 'shiny.js', package = 'shiny'), <a href="#cb29-6" tabindex="-1"></a> css = system.file('www', 'shared', 'shiny.css', package = 'shiny') <a href="#cb29-7" tabindex="-1"></a> )) <a href="#cb29-8" tabindex="-1"></a>}</code></pre></div> See what happens when we print <code>foo</code> objects: <div class="sourceCode" id="cb30"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb30-1" tabindex="-1"></a>new_foo = function(x) structure(x, class = 'foo') <a href="#cb30-2" tabindex="-1"></a>new_foo('hello')</code></pre></div> <blockquote> This is a <code>foo</code> object: hello </blockquote> Check the metadata now: <div class="sourceCode" id="cb31"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb31-1" tabindex="-1"></a>str(knit_meta(clean = FALSE))</code></pre></div> <pre><code>## List of 2 ## $ js : chr "/Users/yihui/R/shiny/www/shared/shiny.js" ## $ css: chr "" ## - attr(*, "knit_meta_id")= chr [1:2] "unnamed-chunk-9" "unnamed-chunk-9"</code></pre> Another <code>foo</code> object: <div class="sourceCode" id="cb33"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb33-1" tabindex="-1"></a>new_foo('world')</code></pre></div> <blockquote> This is a <code>foo</code> object: world </blockquote> Similarly for <code>bar</code> objects: <div class="sourceCode" id="cb34"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb34-1" tabindex="-1"></a>knit_print.bar = function(x, ...) { <a href="#cb34-2" tabindex="-1"></a> asis_output(x, meta = list(head = '<script>console.log("bar!")</script>')) <a href="#cb34-3" tabindex="-1"></a>} <a href="#cb34-4" tabindex="-1"></a>new_bar = function(x) structure(x, class = 'bar') <a href="#cb34-5" tabindex="-1"></a>new_bar('> **hello** world!')</code></pre></div> <blockquote> hello world! </blockquote> <div class="sourceCode" id="cb35"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb35-1" tabindex="-1"></a>new_bar('> hello **world**!')</code></pre></div> <blockquote> hello world! </blockquote> The final version of the metadata, and clean it up: <div class="sourceCode" id="cb36"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb36-1" tabindex="-1"></a>str(knit_meta())</code></pre></div> <pre><code>## List of 6 ## $ js : chr "/Users/yihui/R/shiny/www/shared/shiny.js" ## $ css : chr "" ## $ js : chr "/Users/yihui/R/shiny/www/shared/shiny.js" ## $ css : chr "" ## $ head: chr "<script>console.log(\"bar!\")</script>" ## $ head: chr "<script>console.log(\"bar!\")</script>" ## - attr(*, "knit_meta_id")= chr [1:6] "unnamed-chunk-9" "unnamed-chunk-9" "unnamed-chunk-11" "unnamed-chunk-11" ...</code></pre> <div class="sourceCode" id="cb38"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb38-1" tabindex="-1"></a>str(knit_meta()) # empty now, because clean = TRUE by default</code></pre></div> <pre><code>## list()</code></pre> </div> <div id="for-package-authors" class="section level3"> <h3>For package authors</h3> If you are implementing a custom print method in your own package, here are two tips: <ol style="list-style-type: decimal"> <li>With R >= 3.6.0 (2019-04-26), you can declare the S3 method in the package <code>NAMESPACE</code> with <code>S3method(knitr::knit_print, class)</code>. If you use roxygen2 package, that means a roxygen comment like this: <div class="sourceCode" id="cb40"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb40-1" tabindex="-1"></a>#' @exportS3Method knitr::knit_print <a href="#cb40-2" tabindex="-1"></a>knit_print.class <- </code></pre></div> With this method, you do not need to import knitr to your package, i.e., knitr can be listed in <code>Suggests</code> and not necessarily <code>Imports</code> in the package <code>DESCRIPTION</code>. The S3 methods will be automatically registered when knitr is actually loaded. For R < 3.6.0, you need to import <code>knit_print</code> in your package namespace via <code>importFrom(knitr, knit_print)</code> (or roxygen: <code>#' @importFrom knitr knit_print</code>) (see <a href="https://github.com/yihui/printr">the printr package</a> for an example).</li> <li><code>asis_output()</code> is simply a function that marks an object with the class <code>knit_asis</code>, and you do not have to import this function to your package, either—just let your print method return <code>structure(x, class = 'knit_asis')</code>, and if there are additional metadata, just put it in the <code>knit_meta</code> attribute; here is the source code of this function: <div class="sourceCode" id="cb41"><pre class="sourceCode r"><code class="sourceCode r"><a href="#cb41-1" tabindex="-1"></a>knitr::asis_output</code></pre></div> <pre><code>## function (x, meta = NULL, cacheable = NA) ## { ## structure(x, class = "knit_asis", knit_meta = meta, knit_cacheable = cacheable) ## } ## <bytecode: 0x10b02cb00> ## <environment: namespace:knitr></code></pre> You may put knitr in the <code>Suggests</code> field in <code>DESCRIPTION</code>, and use <code>knitr::asis_output()</code>, so that you can avoid the “hard” dependency on knitr.</li> </ol> </div> </div> <div class="footnotes footnotes-end-of-document"> <hr /> <ol> <li id="fn1">Note R prints an object without an explicit <code>print()</code> call when it is visible; see <code>?invisible</code><a href="#fnref1" class="footnote-back">↩︎</a></li> <li id="fn2">The two hashes <code>##</code> were from the chunk option <code>comment</code>; you can turn them off by <code>comment = ''</code>.<a href="#fnref2" class="footnote-back">↩︎</a></li> </ol> </div> <script type="text/javascript"> window.onload = function() { var i, fig = 1, caps = document.getElementsByClassName('caption'); for (i = 0; i < caps.length; i++) { var cap = caps[i]; if (cap.parentElement.className !== 'figure' || cap.nodeName !== 'P') continue; cap.innerHTML = 'Figure ' + fig + ': ' + cap.innerHTML; fig++; } fig = 1; caps = document.getElementsByTagName('caption'); for (i = 0; i < caps.length; i++) { var cap = caps[i]; if (cap.parentElement.nodeName !== 'TABLE') continue; cap.innerHTML = 'Table ' + fig + ': ' + cap.innerHTML; fig++; } } </script>   <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>