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 xpath
depending 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