用xml2解析html-注释

Question

我开始尝试使用xml2-package来解析一些Rmarkdown Files。现在，我非常热衷于分析html-以结构化的方式解析注释，以及解析各节之间的信息(例如，####等)。

我目前试图访问评论的内容可以在下面找到。

library(xml2)
library(magrittr)

# html-output as created by rmarkdown
x <- xml2::read_xml("
  <div id='header-level-1' class='section level1'>
  <h1>Header Level 1</h1>
  <!-- This is a comment, which I want to parse -->
  <div id='header-level-4-1' class='section level4'>
  <h4>Header Level 4 (1)</h4>
  <!-- parse me 4 (1) -->
  <p>Hello!</p>
  </div>
  <div id='header-level-4-2' class='section level4'>
  <h4>Header Level 4 (2)</h4>
  <!-- parse me 4 (2) -->
  <p>How are you?</p>
  <pre class='r'><code>print(&quot;Hello World&quot;)</code></pre>
  </div>
  </div>
")

# inspecting the structure, {comments} are present as a structural element
x %>% 
  html_structure()
#> <div#header-level-1 .section.level1>
#>   <h1>
#>     {text}
#>   {comment}
#>   <div#header-level-4-1 .section.level4>
#>     <h4>
#>       {text}
#>     {comment}
#>     <p>
#>       {text}
#>   <div#header-level-4-2 .section.level4>
#>     <h4>
#>       {text}
#>     {comment}
#>     <p>
#>       {text}
#>     <pre.r>
#>       <code>
#>         {text}

# first attempt to acess content of comments
x %>% 
  xml_find_all("//div") %>%
  sub("^.*<!-- ", "", .) %>% 
  sub(" -->.*$", "", .)
#> [1] "parse me 4 (2)" "parse me 4 (1)" "parse me 4 (2)"

我敢肯定还有更好的办法吗？理想情况下，我会得到评论，并保持层次结构(这些注释属于哪些标题，例如)

Answer 1

xml_find_all(x, ".//*/comment()/../div")
## {xml_nodeset (2)}
## [1] <div id="header-level-4-1" class="section level4">\n  <h4>Header Level 4 (1)</h4>\n  <!-- parse me 4 (1) -->\n  <p>He ...
## [2] <div id="header-level-4-2" class="section level4">\n  <h4>Header Level 4 (2)</h4>\n  <!-- parse me 4 (2) -->\n  <p>Ho ...