choppervsxml2
Chopper is a tool to extract elements from HTML by preserving ancestors and CSS rules.
Compared to other HTML parsers Chopper is designed to retain original HTML tree but eliminate elements that do not match parsing rules. Meaning, we can parse HTML elements and keep thei structure for machine learning or other tasks where data structure is needed as well as the data value.
The xml2 package is a binding to libxml2, making it easy to work with HTML and XML from R. The API is somewhat inspired by jQuery.
xml2 can be used to parse HTML documents using XPath selectors and is a successor to R's XML package with a few improvements:
- xml2 takes care of memory management for you. It will automatically free the memory used by an XML document as soon as the last reference to it goes away.
- xml2 has a very simple class hierarchy so don't need to think about exactly what type of object you have, xml2 will just do the right thing.
- More convenient handling of namespaces in Xpath expressions - see xml_ns() and xml_ns_strip() to get started.
Example Use
HTML = """
<html>
<head>
<title>Test</title>
</head>
<body>
<div id="header"></div>
<div id="main">
<div class="iwantthis">
HELLO WORLD
<a href="/nope">Do not want</a>
</div>
</div>
<div id="footer"></div>
</body>
</html>
"""
CSS = """
div { border: 1px solid black; }
div#main { color: blue; }
div.iwantthis { background-color: red; }
a { color: green; }
div#footer { border-top: 2px solid red; }
"""
extractor = Extractor.keep('//div[@class="iwantthis"]').discard('//a')
html, css = extractor.extract(HTML, CSS)
# will result in:
html
"""
<html>
<body>
<div id="main">
<div class="iwantthis">
HELLO WORLD
</div>
</div>
</body>
</html>"""
css
"""
div{border:1px solid black;}
div#main{color:blue;}
div.iwantthis{background-color:red;}
"""
library("xml2")
x <- read_xml("<foo> <bar> text <baz/> </bar> </foo>")
x
xml_name(x)
xml_children(x)
xml_text(x)
xml_find_all(x, ".//baz")
h <- read_html("<html><p>Hi <b>!")
h
xml_name(h)