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

[Ben Tupper]

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

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