r - 使用 R 中的 Xpath 根据另一个属性及其父属性获取节点的属性

Question

我有具有以下结构的 xml 文档，我想根据 Balance 属性 bsdate 值和 BalanceRow 属性 rowNum 值选择 valueStart 和 valueEnd 属性值。例如:

• bsdate = '2013' 且 rowNum = '200' valueStart 应为 '3000'，valueEnd - '4000'

• bsdate = '2014' 且 rowNum = '102' valueStart 应为 '5500'，valueEnd - '6500'

可以用R实现吗？我花了一整天的时间寻找答案，但找不到它

    <Root
    xmlns:a="http://www.w3.org/TR/html4/">
    <Balance bsdate = '2013' bsregdate = '2014.04.01'>
        <BalanceRows type = 'B' rowNum = '100' valueStart = '1000' valueEnd = '2000'></BalanceRows>
        <BalanceRows type = 'B' rowNum = '101' valueStart = '3000' valueEnd = '4000'></BalanceRows>
        <BalanceRows type = 'B' rowNum = '102' valueStart = '5000' valueEnd = '6000'></BalanceRows>
        <BalanceRows type = 'P' rowNum = '200' valueStart = '7000' valueEnd = '8000'></BalanceRows>
        <BalanceRows type = 'P' rowNum = '201' valueStart = '9000' valueEnd = '10000'></BalanceRows>
    </Balance>
    <Balance bsdate = '2014' bsregdate = '2015.04.02'>
        <BalanceRows type = 'B' rowNum = '100' valueStart = '1500' valueEnd = '2500' ></BalanceRows>
        <BalanceRows type = 'B' rowNum = '101' valueStart = '3500' valueEnd = '4500'></BalanceRows>
        <BalanceRows type = 'B' rowNum = '102' valueStart = '5500' valueEnd = '6500'></BalanceRows>
        <BalanceRows type = 'P' rowNum = '200' valueStart = '7500' valueEnd = '8500'></BalanceRows>
        <BalanceRows type = 'P' rowNum = '201' valueStart = '9500' valueEnd = '15000'></BalanceRows>
    </Balance>
</Root>

Answer 1

使用测试数据

library(xml2)
xx <- read_xml("<Root xmlns:a=\"http://www.w3.org/TR/html4/\">
  <Balance bsdate = '2013' bsregdate = '2014.04.01'>
  <BalanceRows type = 'B' rowNum = '100' valueStart = '1000' valueEnd = '2000'></BalanceRows>
  <BalanceRows type = 'B' rowNum = '101' valueStart = '3000' valueEnd = '4000'></BalanceRows>
  <BalanceRows type = 'B' rowNum = '102' valueStart = '5000' valueEnd = '6000'></BalanceRows>
  <BalanceRows type = 'P' rowNum = '200' valueStart = '7000' valueEnd = '8000'></BalanceRows>
  <BalanceRows type = 'P' rowNum = '201' valueStart = '9000' valueEnd = '10000'></BalanceRows>
  </Balance>
  <Balance bsdate = '2014' bsregdate = '2015.04.02'>
  <BalanceRows type = 'B' rowNum = '100' valueStart = '1500' valueEnd = '2500' ></BalanceRows>
  <BalanceRows type = 'B' rowNum = '101' valueStart = '3500' valueEnd = '4500'></BalanceRows>
  <BalanceRows type = 'B' rowNum = '102' valueStart = '5500' valueEnd = '6500'></BalanceRows>
  <BalanceRows type = 'P' rowNum = '200' valueStart = '7500' valueEnd = '8500'></BalanceRows>
  <BalanceRows type = 'P' rowNum = '201' valueStart = '9500' valueEnd = '15000'></BalanceRows>
  </Balance>
  </Root>")

您可以通过以下方式获取匹配行的属性

xml_attrs(xml_find_all(xx, "//Balance[@bsdate = '2014']/BalanceRows[@rowNum='200']"))
# [[1]]
#       type     rowNum valueStart   valueEnd 
#       "P"      "200"     "7500"     "8500