html - xpath表达式不起作用

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7年前关闭。

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<p class="c1"><span class="c2">Dokument 1 von 3</span></p>
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<br><p class="c1"><span class="c2">Associated Press Financial Wire</span></p>
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<p class="c1"><span class="c2">April 25, 2012 Wednesday 9:18 PM GMT </span></p>
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<p class="c5"><span class="c6">Apple CEO Tim Cook emerges from Steve Jobs' shadow</span></p>
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<p class="c5"><span class="c7">BYLINE: </span><span class="c2">By PETER SVENSSON, AP Technology Writer</span></p>
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<p class="c5"><span class="c7">SECTION: </span><span class="c2">BUSINESS NEWS</span></p>
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<p class="c5"><span class="c7">LENGTH: </span><span class="c2">794 words</span></p>
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<p class="c5"><span class="c7">DATELINE: </span><span class="c2">NEW YORK </span></p>
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<p class="c8"><span class="c2"> MAIN TEXT 1</span></p>
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<p class="c5"><span class="c7">LOAD-DATE: </span><span class="c2">April 26, 2012</span></p>
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<p class="c5"><span class="c7">LANGUAGE: </span><span class="c2">ENGLISH</span></p>
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<p class="c5"><span class="c7">PUBLICATION-TYPE: </span><span class="c2">Newswire</span></p>
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<br><p class="c1"><span class="c2">Copyright 2012 Associated Press<br>All Rights Reserved</span></p>
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我是XPath的新手，我想结合R（盾灿朗的XML包）使用它来查询我从ListSnExxIS接收到的HTML文档。文档包含多篇新闻文章，每篇文章都由<DOC NUMBER=1> <DOCFULL>标记限定。我想为每个文档提取一些信息，例如，为了提取节信息，我已经做到了：

doc <- htmlParse("hmtldoc.HTML")
xpathSApply(doc,"//span[text()='SECTION: ']/..", xmlValue)

这给了我：

[1] "SECTION: BUSINESS NEWS" "SECTION: BUSINESS NEWS" "SECTION: BUSINESS NEWS"

这是我可以使用的输出。主要的问题是不是每一篇文章都有章节信息。我需要知道的是哪篇文章提供了这些信息，哪些没有，最好是返回NA或空list元素，这样我就可以自己推断出这些信息。
与此问题相关：我试图提出一个解决方案，首先选择DOC或DOCFULL节点，然后从那里继续，例如：

xpathSApply(doc,"//DOCFULL/*/span[text()='SECTION: ']/..", xmlValue)

我认为这应该返回与上面相同的文本，但它没有。无论如何，我对这门语言还是很陌生的，感谢任何帮助。

最佳答案

因为在DOCFULL和span之间有多个“level”子元素，您将需要
含糊其辞

//DOCFULL//*/span[text()='SECTION: ']/..

或者
具体说明级别（div和p）

//DOCFULL/*/*/span[text()='SECTION: ']/..