How to update xml attributes without using a loop with the xml2 R package -


i have xml object update using r's xml2 package. there 2 things need do:

  1. update text inside nodes <c>{text}</c>
  2. update attributes of nodes <c name={text}/>

i'd avoid looping on xml structure because slower identifying node set , assigning entire vector of values @ once.

xml <- read_xml("<root>         <c name='test' db_name='test'><d>this column desc</d></c>         <c name='test2' db_name='test2'><d>this column desc</d></c>         <c name='test3' db_name='test3'><d>this column desc</d></c>     </root>")  df <- data.frame(     db_name = c("test2", "test", "test3"),      desc = c("new desc!", "you want desc", "good vector"),     disp_name = c("okay", "now", "happy"), stringsasfactors = f)

we on #1

c_nodes           <- xml %>% xml_find_all("//c") c_db_names        <- c_nodes %>% xml_find_all("@db_name") %>% xml_text     xml_text(c_nodes) <- df$desc[match(c_db_names, df$db_name)]

bad on #2

disp_names <- df$disp_name[match(c_db_names, df$db_name)]  (i in seq_along(c_nodes)) {   xml_attr(c_nodes[i], "name") <- disp_names[i] }

when try xml_attr(c_nodes, "name") <- df$disp_name[match(c_db_names, df$db_name)], following error:

error in node_set_attr(x$node, name = attr, nsmap = ns, value) : expecting single value

if provide single value updates entire node set 1 value, need make different updates each node attribute. thus, i'm using loop, want replace vectorized equivalent produce this:

{xml_document} <root> [1] <c name="now" db_name="test">\n  <d>you want desc</d>\n</c> [2] <c name="okay" db_name="test2">\n  <d>new desc!</d>\n</c> [3] <c name="happy" db_name="test3">\n  <d>good vector</d>\n</c>

xml_set_attrs correct function use, must pass in list of named character vectors value parameter. can create list using apply function, , pass function follows:

new_attrs<-lapply(df$disp_name[match(c_db_names, df$db_name)],                    function(x) {                                 names(x)<- "name"                                 x                                })  xml_set_attrs(c_nodes, new_attrs)

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