Isolating data from single XML nodeset in R xml2 - r

Question

I am trying to iteratively isolate and manipulate nodesets from an XML document, but I am getting a strange behavior in the xml_find_all() function in the xml2 package in R. Can someone please help me understand the scope of functions applied to a nodeset?
Here is an example:
library( xml2 )
library( dplyr )
doc <- read_xml( "<MEMBERS>
<CUSTOMER>
<ID>178</ID>
<FIRST.NAME>Alvaro</FIRST.NAME>
<LAST.NAME>Juarez</LAST.NAME>
<ADDRESS>123 Park Ave</ADDRESS>
<ZIP>57701</ZIP>
</CUSTOMER>
<CUSTOMER>
<ID>934</ID>
<FIRST.NAME>Janette</FIRST.NAME>
<LAST.NAME>Johnson</LAST.NAME>
<ADDRESS>456 Candy Ln</ADDRESS>
<ZIP>57701</ZIP>
</CUSTOMER>
</MEMBERS>" )
doc %>% xml_find_all( '//*') %>% xml_path()
# [1] "/MEMBERS" "/MEMBERS/CUSTOMER[1]"
# [3] "/MEMBERS/CUSTOMER[1]/ID" "/MEMBERS/CUSTOMER[1]/FIRST.NAME"
# [5] "/MEMBERS/CUSTOMER[1]/LAST.NAME" "/MEMBERS/CUSTOMER[1]/ADDRESS"
# [7] "/MEMBERS/CUSTOMER[1]/ZIP" "/MEMBERS/CUSTOMER[2]"
# [9] "/MEMBERS/CUSTOMER[2]/ID" "/MEMBERS/CUSTOMER[2]/FIRST.NAME"
#[11] "/MEMBERS/CUSTOMER[2]/LAST.NAME" "/MEMBERS/CUSTOMER[2]/ADDRESS"
#[13] "/MEMBERS/CUSTOMER[2]/ZIP"
The object customer.01 is a nodeset that contains data from that customer only.
kids <- xml_children( doc )
customer.01 <- kids[[1]]
customer.01
# {xml_node}
# <CUSTOMER>
# [1] <ID>178</ID>
# [2] <FIRST.NAME>Alvaro</FIRST.NAME>
# [3] <LAST.NAME>Juarez</LAST.NAME>
# [4] <ADDRESS>123 Park Ave</ADDRESS>
# [5] <ZIP>57701</ZIP>
Why does the function, applied to the customer.01 nodeset, return the ID for customer.02 as well?
xml_find_all( customer.01, "//MEMBERS/CUSTOMER/ID" )
# {xml_nodeset (2)}
# [1] <ID>178</ID>
# [2] <ID>934</ID>
How do I return only values from that nodeset?
~~~
Ok, so here's a small wrinkle in the solution below, again related to scope of the xml_find_all() function. It says that it can be applied to a document, node, or nodeset. However...
This case works when applied to a nodeset:
library( xml2 )
url <- "https://s3.amazonaws.com/irs-form-990/201501279349300635_public.xml"
doc <- read_xml( url )
xml_ns_strip( doc )
nd <- xml_find_all( doc, "//LiquidationOfAssetsDetail|//LiquidationDetail" )
nodei <- nd[[1]]
nodei
# {xml_node}
# <LiquidationOfAssetsDetail>
# [1] <AssetsDistriOrExpnssPaidDesc>LAND</AssetsDistriOrExpnssPaidDesc>
# [2] <DistributionDt>2014-11-04</DistributionDt>
# [3] <MethodOfFMVDeterminationTxt>SEE ATTACH</MethodOfFMVDeterminationTxt>
# [4] <EIN>abcdefghi</EIN>
# [5] <BusinessName>\n <BusinessNameLine1Txt>GREENSBURG PUBLIC LIBRARY</BusinessNameLine1Txt>\n</BusinessName>
# [6] <USAddress>\n <AddressLine1Txt>1110 E MAIN ST</AddressLine1Txt>\n <CityNm>GREENSBURG</CityNm>\n <StateAbbreviationCd>IN</StateAb ...
# [7] <IRCSectionTxt>501(C)(3)</IRCSectionTxt>
xml_text( xml_find_all( nodei, "AssetsDistriOrExpnssPaidDesc" ) )
# [1] "LAND"
But not this one:
nodei <- xml_children( nd[[i]] )
nodei
# {xml_nodeset (7)}
# [1] <AssetsDistriOrExpnssPaidDesc>LAND</AssetsDistriOrExpnssPaidDesc>
# [2] <DistributionDt>2014-11-04</DistributionDt>
# [3] <MethodOfFMVDeterminationTxt>SEE ATTACH</MethodOfFMVDeterminationTxt>
# [4] <EIN>abcdefghi</EIN>
# [5] <BusinessName>\n <BusinessNameLine1Txt>GREENSBURG PUBLIC LIBRARY</BusinessNameLine1Txt>\n</BusinessName>
# [6] <USAddress>\n <AddressLine1Txt>1110 E MAIN ST</AddressLine1Txt>\n <CityNm>GREENSBURG</CityNm>\n <StateAbbreviationCd>IN</StateAb ...
# [7] <IRCSectionTxt>501(C)(3)</IRCSectionTxt>
xml_text( xml_find_all( nodei, "AssetsDistriOrExpnssPaidDesc" ) )
# character(0)
I'm guessing this is a problem applying xml_find_all() to all elements of a nodeset rather than a scoping issue?

Answer 1

Currently, you are using the absolute path search from root with XPath's double forward slash, //, which means find all items in document that match this path which includes both customers' ID.
For particular child nodes under a specific node, simply use a relative path under selected node:
xml_find_all(customer.01, "ID")
# {xml_nodeset (1)}
# [1] <ID>178</ID>
xml_find_all(customer.01, "FIRST.NAME|LAST.NAME")
# {xml_nodeset (2)}
# [1] <FIRST.NAME>Alvaro</FIRST.NAME>
# [2] <LAST.NAME>Juarez</LAST.NAME>
xml_find_all(customer.01, "*")
# {xml_nodeset (5)}
# [1] <ID>178</ID>
# [2] <FIRST.NAME>Alvaro</FIRST.NAME>
# [3] <LAST.NAME>Juarez</LAST.NAME>
# [4] <ADDRESS>123 Park Ave</ADDRESS>
# [5] <ZIP>57701</ZIP>