我对使用 R 很陌生，对使用 XML 包和 xpath 也很陌生。我需要从一个如下所示的 xml 文件中提取四个元素(除了我已经剪掉了很多其他 xmlnode 以在此处简化它):

<?xml version="1.0" encoding="utf-8"?>
<iati-activities version="1.03" generated-datetime="2015-07-07T16:49:09+00:00">
  <iati-activity last-updated-datetime="2014-08-11T14:36:59+00:00" xml:lang="en" default-currency="EUR">
<iati-identifier>NL-KVK-41160054-100530</iati-identifier>
<title>Improvement of basic health care</title>
<reporting-org ref="NL-KVK-41160054" type="21">Stichting Cordaid</reporting-org>
<participating-org role="Accountable" ref="NL-KVK-41160054" type="21">Cordaid</participating-org>
<participating-org role="Funding" ref="EU" type="15">EU</participating-org>
<participating-org role="Funding" type="21">Cordaid Memisa</participating-org>
<participating-org role="Funding" ref="NL-1" type="10">Dutch Ministry of Foreign Affairs</participating-org>
<participating-org role="Implementing" type="21">CORDAID RCA</participating-org>
<recipient-country percentage="100" code="CF">CENTRAL AFRICAN REPUBLIC</recipient-country>
<budget type="1">
  <period-start iso-date="2010-01-01"></period-start>
  <period-end iso-date="2013-02-28"></period-end>
</budget>
  </iati-activity>
  <iati-activity last-updated-datetime="2013-07-19T14:12:14+00:00" xml:lang="en" default-currency="EUR">
<iati-identifier>NL-KVK-41160054-100625</iati-identifier>
<title>Pigs for Pencils</title>
<reporting-org ref="NL-KVK-41160054" type="21">Stichting Cordaid</reporting-org>
<participating-org role="Funding" ref="NL-1" type="10">Dutch Ministry of Foreign Affairs</participating-org>
<participating-org role="Funding" type="60">Stichting Kapatiran</participating-org>
<participating-org role="Implementing" type="22">PREDA Foundation Inc.</participating-org>
<participating-org role="Accountable" ref="NL-KVK-41160054" type="21">Cordaid</participating-org>
<budget type="2">
  <period-start iso-date="2010-04-20"></period-start>
  <period-end iso-date="2012-10-02"></period-end>
  <value value-date="2010-04-20">12500</value>
</budget>
   </iati-activity>
  <iati-activity last-updated-datetime="2015-04-08T03:01:58+00:00" xml:lang="en" default-currency="EUR">
    <iati-identifier>NL-KVK-41160054-100815</iati-identifier>
<title>Job and housing opportunities for women </title>
<reporting-org ref="NL-KVK-41160054" type="21">Stichting Cordaid</reporting-org>
<participating-org role="Funding" ref="NL-1" type="10">Dutch Ministry of Foreign Affairs</participating-org>
<participating-org role="Implementing" type="22">WISE</participating-org>
<participating-org role="Accountable" ref="NL-KVK-41160054" type="21">Cordaid</participating-org>
<budget type="2">
  <period-start iso-date="2010-10-01"></period-start>
  <period-end iso-date="2011-12-31"></period-end>
  <value value-date="2010-10-01">227000</value>
</budget>
  </iati-activity>
</iati-activities>

这也是我在 StackOverflow 上提出的第一个问题，如果我没有正确地做(而且 xml 没有完全对齐)，我深表歉意。 我需要的元素以及我分配给它们的是:

UniqueID <- "//iati-activity/iati-identifier"

GrantTitle <- "//iati-activity/title"

GrantAmount <- "//iati-activity/budget/value"

Recipient <- "//iati-activity/participatingorg[@role='Implementing']"

到目前为止(经过多次试验和磨难)我想出了这段代码，它遍历当前节点 (x)，拉出 4 个变量，并将它们绑定(bind)成一行，然后使用 xpathApply 循环 iati-事件节点调用该函数并将结果行绑定(bind)在一起。

当所有四个元素都存在于每个事件中时，此代码有效。但是，请注意 xml 示例中没有预算/值(value)节点。这是因为我删除它是为了解决这个缺少节点的问题，这个问题在我需要的几乎所有元素的完整文件中经常出现。

另请注意我的 xpath 表达式末尾的 [1] - 我将这些包括在内是因为还有多个标题、多个所有类型的参与组织等。

鉴于某些元素的倍数和其他元素的不存在，不可能将所有相同的元素简单地拉入一个向量并将其弹出到一个数据框中。因此需要遍历每个事件来拉动它的元素。我的代码目前无法解决缺失的元素(第一个 iati 事件中缺失的预算/值)，因为 cbinding(和 rbinding)忽略空向量。

xmltestNA = xmlInternalTreeParse("XMLtoDF_TestNA.xml", useInternalNodes=TRUE)
bodyToDF <- function(x){
  UniqueID <- xpathSApply(x, "./iati-identifier", xmlValue)
  GrantTitle <- xpathSApply(x, "./title[1]", xmlValue)
  GrantAmount <- xpathSApply(x, "./budget/value[1]", xmlValue)
  Recipient <- xpathSApply(x, "./participating-org[@role='Implementing'][1]", xmlValue)
  cbind(UniqueID=UniqueID, GrantTitle=GrantTitle, GrantAmount=GrantAmount, Recipient=Recipient)
  }
res <-xpathApply(xmltestNA, '//iati-activity', fun=bodyToDF)
IatiNA <-do.call(rbind, res)
IatiNA

如何保留空值/缺失节点，以便将其转换为如下所示的矩阵或数据框:

    UniqueID    GrantTitle  GrantAmount Recipient
1   NL-KVK-41160054-100530  Improvement of basic health care    NA  CORDAID RCA
2   NL-KVK-41160054-100625  Pigs for Pencils    12500   PREDA Foundation Inc.
3   NL-KVK-41160054-100815  Job and housing opportunities for women     227000  WISE

因为我还是新手，所以代码越简单越好。提前致谢!

最佳答案

如果您的 xpath 查询返回的结果太多或太少，我认为使用节点会更容易

doc <- xmlParse( '<your xml here>')
nodes<- getNodeSet(doc, "//iati-activity")

#Compare
xpathSApply(doc, "//budget/value", xmlValue)
xpathSApply(doc, "//participating-org[@role='Funding']", xmlValue)

sapply(nodes, function(x) xpathSApply(x, "./budget/value", xmlValue))
sapply(nodes, function(x) xpathSApply(x, "./participating-org[@role='Funding']", xmlValue))

添加一个函数来处理缺失或多个节点，然后创建 data.frame

xpath2 <-function(x, path, fun = xmlValue, ...){
   y <- xpathSApply(x, path, fun, ...)
   ifelse(length(y) == 0, NA,
    ifelse(length(y) > 1, paste(unlist(y), collapse=", "), y))
}

GrantAmount <- sapply(nodes, xpath2, "./budget/value")
UniqueID    <- sapply(nodes, xpath2, "./iati-identifier")
GrantTitle  <- sapply(nodes, xpath2, "./title")
Recipient   <-  sapply(nodes, xpath2, "./participating-org[@role='Implementing']")
## updated xpath2 so xmlGetAttr will also work
Funding_ref  <- sapply(nodes, xpath2, "./participating-org[@role='Funding']", xmlGetAttr, "ref")
Budget_start <- sapply(nodes, xpath2, ".//period-start", xmlGetAttr, "iso-date")

data.frame(UniqueID, GrantTitle, GrantAmount, Recipient)
                UniqueID                               GrantTitle GrantAmount             Recipient
1 NL-KVK-41160054-100530         Improvement of basic health care        <NA>           CORDAID RCA
2 NL-KVK-41160054-100625                         Pigs for Pencils       12500 PREDA Foundation Inc.
3 NL-KVK-41160054-100815 Job and housing opportunities for women       227000                  WISE

关于xml - R-XML 将节点拉入矩阵/DF 以解决丢失的节点，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31999486/