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

[Ben Tupper]

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 <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> 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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> 
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
> 
>  
> Ben Tupper
> Bigelow Laboratory for Ocean Sciences
> 60 Bigelow Drive, P.O. Box 380
> East Boothbay, Maine 04544
> http://www.bigelow.org <http://www.bigelow.org/>
>  
> Tick Forecasting: https://eco.bigelow.org/ <https://eco.bigelow.org/>
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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