R dataframe from XML when values are multiple or missing

Question

This question is similar to a previous question, Import all fields (and subfields) of XML as dataframe, but I want to pull out only a subset of the XML data and want to incl

Answer 1

If you're looking to exactly reproduce the desired output you showed in your question, you can convert your XML to a list and then extract the information you want:

xml_list <- xmlToList(xmlParse(xml_data))

First loop through each "building" node and remove those that contain "station":

xml_list <- lapply(xml_list, lapply, function(x) {
  x[!sapply(x, function(y) any(y == "station"))]
})

Then collect data for each city into a data frame

xml_list <- lapply(xml_list, function(x) {
  bldgs <- unlist(x$buildings)
  bldgs <- bldgs[bldgs != "landmark"]
  if(is.null(bldgs)) bldgs <- NA
  data.frame(
    "city" = x$name,
    "landmark" = bldgs,
    stringsAsFactors = FALSE)
})

Then combine information from all cities together:

xml_output <- do.call("rbind", xml_list)
xml_output
           city     landmark
city     London Tower Bridge
city1  New York         
city.1    Paris Eiffel Tower
city.2    Paris       Louvre