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xmlr

An Element has three “interests”, name, attributes and child nodes. text is handled in a special way (there is a Text class) since the form <foo>Som text here</foo> is very common.

This set the name of the Element (the tag) e.g. to create the element you can either do e <- Element$new("foo") or use the setName(name) function:

e <- Element$new()
e$setName("foo")

To get the Element name you use the function getName()

The following functions are available for attributes:

• getAttribute(name) This gets the attribute value for the name argument supplied, e.g. child$getAttribute("class")
• getAttributes() This gives you the list of attributes for this Element. You can navigate the list just like normal e.g. child$getAttributes()[["class"]] or use in a loop or apply etc.
• setAttribute(name, value) Creates or updates an existing attribute for the name and value supplied. E.g. root$setAttribute("xmlns", "http://www.w3.org/TR/html4/").
• setAttributes(attributes) This sets all the attributes of the Element to the list given. Note that you MUST supply a named list for this to work. Any existing attribute will vanish.
• addAttributes(attributes) Similar to setAttributes but will not erase any existing attributes.
• hasAttributes() TRUE if any attributes are defined for the element.

Content can be either other Element(s) or Text.

For the xml

<foo>
  <Bar note='Some text'</Bar>
  <Baz note='More stuff'</Baz>
</foo>

…you can do something like this:

e <- Element$new("foo")$addContent(
  Element$new("Bar")$setAttribute("note", "Some text")
)$addContent(
  Element$new("Baz")$setAttribute("note", "More stuff")
)
e
#> <foo><Bar note='Some text'></Bar><Baz note='More stuff'></Baz></foo>

To retrieve content there are several ways:

• getContent() This will get you the complete list of content regardless if they are Elements or Text nodes.
• getChildren() This will give you a list of Elements belonging to this element.
• removeContent(content) This will remove the content supplied from this Elements content list.
• removeContentAt(index) Same as above but for the position in the list matching the index supplied.
• contentIndex(content) Gives you the index of the content supplied or -1 if no content was found.
• getChild(name) Gives you the first occurrence of the Element that is a child of this element with the name matching the name supplied
• hasContent() TRUE if there is any content belonging to this element
• hasChildren() TRUE if there is any child elements for this element

As mentioned above Text is treated a bit special. You typically use the setText(text) function to set text content e.g. to create <car>Volvo</car> you would do:

e <- Element$new("car")$setText("Volvo")

However, for more complex cases it is possible to mix text and elements using addContent(). E.g. for the xml <cars>Volvo<value sek='200000'></value></cars>

You can create it by creating and adding a Text node explicitly rather than using the setText function.

  xml <- "<car>Volvo<value sek='200000'></value></car>"
  e <- Element$new("car")
  e$addContent(Text$new("Volvo"))
  e$addContent(Element$new("value")$setAttribute("sek", "200000"))
  stopifnot(e$toString() == xml)

To check if there is any text defined for this element you can use the function hasText()

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