R中的XML处理：在子节点中使用xmlGetAttr

我有几个XML文件，其结构类似于以下文件：

<?xml version='1.0' encoding='UTF-8'?> 

<text>

  <stage></stage>

    <div>
      <intro agent= "Peter"></intro>
        <dialogue agent= "Peter"></dialogue>
      <outro agent= "Stephen"></outro>
    </div>

    <div>
     <intro agent= "Sandra"></intro>
        <dialogue agent= "Peter"></dialogue>
     <outro agent= "Robert"></outro>
    </div>

  <stage></stage>

</text>

---

我认为现在应该更多地关注XPath而不是R：

txt <- '<?xml version="1.0" encoding="UTF-8"?> 
<text>
  <stage></stage>
    <div>
      <intro agent= "Peter"></intro>
        <dialogue agent= "Peter"></dialogue>
      <outro agent= "Stephen"></outro>
    </div>
    <div>
     <intro agent= "Sandra"></intro>
        <dialogue agent= "Peter"></dialogue>
     <outro agent= "Robert"></outro>
    </div>
  <stage></stage>
</text>'

library(xml2)
library(magrittr)

doc <- read_xml(txt)
xml_find_all(doc, ".//*[@agent]") %>% 
  xml_attr("agent")

---

我认为现在应该更多地关注XPath而不是R：

txt <- '<?xml version="1.0" encoding="UTF-8"?> 
<text>
  <stage></stage>
    <div>
      <intro agent= "Peter"></intro>
        <dialogue agent= "Peter"></dialogue>
      <outro agent= "Stephen"></outro>
    </div>
    <div>
     <intro agent= "Sandra"></intro>
        <dialogue agent= "Peter"></dialogue>
     <outro agent= "Robert"></outro>
    </div>
  <stage></stage>
</text>'

library(xml2)
library(magrittr)

doc <- read_xml(txt)
xml_find_all(doc, ".//*[@agent]") %>% 
  xml_attr("agent")

agents <- xmlApply(xml_processed[["test.xml"]], "/text/div/intro", xmlGetAttr, "agent", default= "-")

get(as.character(FUN), mode = "function", envir = envir)

txt <- '<?xml version="1.0" encoding="UTF-8"?> 
<text>
  <stage></stage>
    <div>
      <intro agent= "Peter"></intro>
        <dialogue agent= "Peter"></dialogue>
      <outro agent= "Stephen"></outro>
    </div>
    <div>
     <intro agent= "Sandra"></intro>
        <dialogue agent= "Peter"></dialogue>
     <outro agent= "Robert"></outro>
    </div>
  <stage></stage>
</text>'

library(xml2)
library(magrittr)

doc <- read_xml(txt)
xml_find_all(doc, ".//*[@agent]") %>% 
  xml_attr("agent")

library(XML)

doc <- xmlParse(txt)
xpathSApply(doc, "//*[@agent]", xmlGetAttr, "agent")