Select elements from an HTML document — html_element (original) (raw)

html_element() and html_elements() find HTML element using CSS selectors or XPath expressions. CSS selectors are particularly useful in conjunction with https://selectorgadget.com/, which makes it very easy to discover the selector you need.

Usage

html_element(x, css, xpath)

html_elements(x, css, xpath)

Arguments

x

Either a document, a node set or a single node.

css, xpath

Elements to select. Supply one of css or xpathdepending on whether you want to use a CSS selector or XPath 1.0 expression.

Value

html_element() returns a nodeset the same length as the input.html_elements() flattens the output so there's no direct way to map the output to the input.

CSS selector support

CSS selectors are translated to XPath selectors by the selectrpackage, which is a port of the python cssselect library,https://pythonhosted.org/cssselect/.

It implements the majority of CSS3 selectors, as described inhttps://www.w3.org/TR/2011/REC-css3-selectors-20110929/. The exceptions are listed below:

• Pseudo selectors that require interactivity are ignored::hover, :active, :focus, :target, :visited.
• The following pseudo classes don't work with the wild card element, *:*:first-of-type, *:last-of-type, *:nth-of-type,*:nth-last-of-type, *:only-of-type
• It supports :contains(text)
• You can use !=, [foo!=bar] is the same as :not([foo=bar])
• :not() accepts a sequence of simple selectors, not just a single simple selector.

Examples

html <- minimal_html("
  <h1>This is a heading</h1>
  <p id='first'>This is a paragraph</p>
  <p class='important'>This is an important paragraph</p>
")

html %>% html_element("h1")
#> {html_node}
#> <h1>
html %>% html_elements("p")
#> {xml_nodeset (2)}
#> [1] <p id="first">This is a paragraph</p>
#> [2] <p class="important">This is an important paragraph</p>
html %>% html_elements(".important")
#> {xml_nodeset (1)}
#> [1] <p class="important">This is an important paragraph</p>
html %>% html_elements("#first")
#> {xml_nodeset (1)}
#> [1] <p id="first">This is a paragraph</p>

# html_element() vs html_elements() --------------------------------------
html <- minimal_html("
  <ul>
    <li><b>C-3PO</b> is a <i>droid</i> that weighs <span class='weight'>167 kg</span></li>
    <li><b>R2-D2</b> is a <i>droid</i> that weighs <span class='weight'>96 kg</span></li>
    <li><b>Yoda</b> weighs <span class='weight'>66 kg</span></li>
    <li><b>R4-P17</b> is a <i>droid</i></li>
  </ul>
")
li <- html %>% html_elements("li")

# When applied to a node set, html_elements() returns all matching elements
# beneath any of the inputs, flattening results into a new node set.
li %>% html_elements("i")
#> {xml_nodeset (3)}
#> [1] <i>droid</i>
#> [2] <i>droid</i>
#> [3] <i>droid</i>

# When applied to a node set, html_element() always returns a vector the
# same length as the input, using a "missing" element where needed.
li %>% html_element("i")
#> {xml_nodeset (4)}
#> [1] <i>droid</i>
#> [2] <i>droid</i>
#> [3] NA
#> [4] <i>droid</i>
# and html_text() and html_attr() will return NA
li %>% html_element("i") %>% html_text2()
#> [1] "droid" "droid" NA      "droid"
li %>% html_element("span") %>% html_attr("class")
#> [1] "weight" "weight" "weight" NA