[R] how to add a child to a child in XML

[Bond, Stephen]

Just to clarify and hopefully catch the attention of the maintainer:

The newXMLNode function is not mentioned in:

https://cran.r-project.org/web/packages/XML/XML.pdf

which supposedly describes all functions in the package.


Stephen

From: Ben Tupper [mailto:btupper at bigelow.org]
Sent: Thursday, March 22, 2018 10:40 AM
To: Bond, Stephen
Cc: r-help
Subject: Re: [R] how to add a child to a child in XML

Hi,

It's a reasonable question. The answer is that it actually is included, but there are many instances across packages where multiple functions are documented on a single help page.  The following brings up such a page... (for XML_3.98-1.9)

> library(XML)
> ?newXMLNode

You can see the same on line...

https://www.rdocumentation.org/packages/XML/versions/3.98-1.9/topics/newXMLDoc

You have dig in to find it.

If you are just starting out with XML, you might want to spend some time comparison shopping with the xml2 package. https://www.rdocumentation.org/packages/xml2/versions/1.2.0  I like each one, and I use both XML and xml2 (not at the same time). I have been slowly migrating toward xml2 as I use more of the tidyverse stuff.

Cheers,
Ben

On Mar 22, 2018, at 9:19 AM, Bond, Stephen <Stephen.Bond at cibc.com<mailto:Stephen.Bond at cibc.com>> wrote:

Big thanks. newXMLNode works great. Wonder why it is not included in the documentation.
There is newXMLDoc and newXMLNamespace, but no mention of newXMLNode.

Stephen

From: Ben Tupper [mailto:btupper at bigelow.org]
Sent: Wednesday, March 21, 2018 6:18 PM
To: Bond, Stephen
Cc: r-help
Subject: Re: [R] how to add a child to a child in XML

Hi,

XML doesn't use the `$` to access child nodes.  Instead use either `[name]` to get a list of children of that name or `[[name]]` to get the just the first child of that name encountered in the genealogy.  Thus for your example...

> root$child1
NULL

> root[['child1']]
<child1 name1="A" name2="B" name3="C"/>


On the other hand, you might consider using newXMLNode() instead of xmlNode() as it accepts a "parent = " argument.  The alternative using newXMLNode() would look like...

atts_root <- c("val1","val2","val3")
names(atts_root) <- c("att1","att2","att3")
root <- newXMLNode("root", attrs = atts_root)

atts_child <- LETTERS[1:3]
names(atts_child) <- paste("name",1:3,sep="")
child <- newXMLNode("child",attrs = atts_child, parent = root)

atts_grandchild <- letters[1:3]
names(atts_grandchild) <- paste("name",4:6,sep="")
grandchild <- newXMLNode("grandchild",attrs = atts_grandchild, parent = child)

root
#<root att1="val1" att2="val2" att3="val3">
#  <child name1="A" name2="B" name3="C">
#    <grandchild name4="a" name5="b" name6="c"/>
#  </child>
#</root>


Cheers,
Ben

On Mar 21, 2018, at 4:25 PM, Bond, Stephen <Stephen.Bond at cibc.com<mailto:Stephen.Bond at cibc.com>> wrote:

I am trying to add a child to a child using XML package in R. the following fails

library(XML)

node1 <- c("val1","val2","val3")

names(node1) <- c("att1","att2","att3")

root <- xmlNode("root", attrs=node1)

node2 <- LETTERS[1:3]

names(node2) <- paste("name",1:3,sep="")

root <- addChildren(root,xmlNode("child1",attrs=node2))

node3 <- letters[1:3]

names(node3) <- paste("name",4:6,sep="")

root <- addChildren(root$child1,xmlNode("child2",attrs=node3))



Error in UseMethod("addChildren") : no applicable method for 'addChildren' applied to an object of class "NULL"


Stephen B


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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org

Tick Forecasting: https://eco.bigelow.org/




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