如何将XML的一部分转换为数据框？ (正确)

发布时间：2020-12-16 07:59:27 所属栏目：百科来源：网络整理

导读：我试图从ClinicalTrials.gov的XML文件中提取信息.该文件按以下方式组织： clinical_study ... brief_title ... location facility name address city state zip country /facility status contact last_name phone email /contact /location location ... /l

我试图从ClinicalTrials.gov的XML文件中提取信息.该文件按以下方式组织：

<clinical_study>
  ...
  <brief_title>
  ...
  <location>
    <facility>
      <name>
      <address>
        <city>
        <state>
        <zip>
        <country>
    </facility>
    <status>
    <contact>
      <last_name>
      <phone>
      <email>
    </contact>
  </location>
  <location>
    ...
  </location>
  ...
</clinical_study>

我可以在以下代码中使用CRAN的R XML包从XML文件中提取所有位置节点：

library(XML)
clinicalTrialUrl <- "http://clinicaltrials.gov/ct2/show/NCT01480479?resultsxml=true"
xmlDoc <- xmlParse(clinicalTrialUrl,useInternalNode=TRUE)
locations <- xmlToDataFrame(getNodeSet(xmlDoc,"//location"))

这样做很好.但是,如果您查看数据框,您会注意到xmlToDataFrame函数将< facility>下的所有内容集中在一起.成一个连接的字符串.解决方案是编写代码以逐列生成数据框,例如,您可以生成

您可以先将XML展平.

flatten_xml <- function(x) {
  if (length(xmlChildren(x)) == 0) structure(list(xmlValue(x)),.Names = xmlName(xmlParent(x)))
  else Reduce(append,lapply(xmlChildren(x),flatten_xml))
}

dfs <- lapply(getNodeSet(xmlDoc,"//location"),function(x) data.frame(flatten_xml(x)))
allnames <- unique(c(lapply(dfs,colnames),recursive = TRUE))
df <- do.call(rbind,lapply(dfs,function(df) { df[,setdiff(allnames,colnames(df))] <- NA; df }))
head(df)

 #          city      state   zip       country     status          last_name        phone                    email               last_name.1
 # 1  Birmingham    Alabama 35294 United States Recruiting Louis B Nabors,MD 205-934-1813          bnabors@uab.edu        Louis B Nabors,MD
 # 2      Mobile    Alabama 36604 United States Recruiting Melanie Alford,RN 251-445-9649     malford@usouthal.edu    Pamela Francisco,CCRP
 # 3     Phoenix    Arizona 85013 United States Recruiting     Lynn Ashby,MD 602-406-6262           LASHBY@CHW.EDU            Lynn Ashby,MD
 # 4      Tucson    Arizona 85724 United States Recruiting         Jamie Holt 520-626-6800 jholt1@email.arizona.edu Baldassarre Stea,MD,PhD
 # 5 Little Rock   Arkansas 72205 United States Recruiting   Wilma Brooks,RN 501-686-8530       ALEubanks@uams.edu       Amanda Eubanks,APN
 # 6    Berkeley California 94704 United States  Withdrawn               <NA>         <NA>                     <NA>                      <NA>

（编辑：李大同）

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