xml to R dataframe, multiple layers of children - r

Question

I was trying to convert an xml into r df using XML package. Was able to get a df successfully, but whenever there were grandchildren under a child, values of grandchildren was merged into one column.
Here is how the xml looks like:
<user>
<created-at type="datetime">2012-12-20T18:32:20+00:00</created-at>
<details></details>
<is-active type="boolean">true</is-active>
<last-login type="datetime">2017-06-22T16:52:11+01:00</last-login>
<time-zone>Pacific Time (US & Canada)</time-zone>
<updated-at type="datetime">2017-06-22T21:00:47+01:00</updated-at>
<is-verified type="boolean">true</is-verified>
<groups type="array">
<group>
<created-at type="datetime">2015-02-09T09:34:41+00:00</created-at>
<id type="integer">23215935</id>
<is-active type="boolean">true</is-active>
<name>Product Managers</name>
<updated-at type="datetime">2015-02-09T09:34:41+00:00</updated-at>
</group>
</groups>
</user>
The code I used were:
users_xml = xmlTreeParse("users.xml")
top_users = xmlRoot(users_xml)
users = xmlSApply(top_users, function(x) xmlSApply(x, xmlValue))
The result I got had all the elements listed fine besides it combined everything under "groups" into one column. Is there anyway I can make each element under "group" a separate column in the final dataframe?
I also tried
nodes=getNodeSet(top_users, "//groups[#group]")
and
nodes=getNodeSet(top_users, "//groups/group[#group]")
and
nodes=getNodeSet(top_users, "//.groups/group[#group]")
and switched "top_users" to "user_xml", but each time got error message:
Error: 1: Input is not proper UTF-8, indicate encoding !
Bytes: 0xC2 0x3C 0x2F 0x6E
Then tried
data.frame(t(xpathSApply(xmlRoot(xmlTreeParse("users.xml", useInternalNodes = T)),
"//user", function(y) xmlSApply(y, xmlValue))))
Which gave me the exact same thing as the first solution.
And finally, I tried
data.frame(t(xpathSApply(xmlRoot(xmlTreeParse("users.xml", useInternalNodes = T)),
"//user/groups/group", function(y) xmlSApply(y, xmlValue))))
Which did give me a dataframe but only with elements in "group", and there is no way I can map it back to the first table I got that has all elements in "user".

Answer 1

Consider column binding with xmlToDataFrame() of user children and groups children:
userdf <- xmlToDataFrame(nodes=getNodeSet(doc, "/user"))
groupdf <- xmlToDataFrame(nodes=getNodeSet(doc, "/user/groups/group"))
df <- transform(cbind(userdf, groupdf), groups = NULL) # REMOVE groups COL
df
# created.at details is.active last.login time.zone
# 1 2012-12-20T18:32:20+00:00 true 2017-06-22T16:52:11+01:00 Pacific Time (US & Canada)
# updated.at is.verified created.at.1 id is.active.1 name
# 1 2017-06-22T21:00:47+01:00 true 2015-02-09T09:34:41+00:00 23215935 true Product Managers
# updated.at.1
# 1 2015-02-09T09:34:41+00:00