我之前已经使用过XML包来解析HTML和XML，并且对xPath有了初步的掌握。然而，我被要求考虑 XML 数据，其中重要位是由元素本身以及相关节点中的文本和属性的组合确定的。我从来没有这样做过。例如
[更新的示例，稍微更广泛]
<Catalogue>
<Bookstore id="ID910705541">
<location>foo bar</location>
<books>
<book category="A" id="1">
<title>Alpha</title>
<author ref="1">Matthew</author>
<author>Mark</author>
<author>Luke</author>
<author ref="2">John</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="B" id="10">
<title>Beta</title>
<author ref="1">Huey</author>
<author>Duey</author>
<author>Louie</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="D" id="100">
<title>Gamma</title>
<author ref="1">Tweedle Dee</author>
<author ref="2">Tweedle Dum</author>
<year>2005</year>
<price>29.99</price>
</book>
</books>
</Bookstore>
<Bookstore id="ID910700051">
<location>foo</location>
<books>
<book category="A" id="1">
<title>Happy</title>
<author>Dopey</author>
<author>Bashful</author>
<author>Doc</author>
<author ref="1">Grumpy</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="B" id="10">
<title>Ni</title>
<author ref="1">John</author>
<author ref="2">Paul</author>
<author ref="3">George</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="D" id="100">
<title>San</title>
<author ref="1">Ringo</author>
<year>2005</year>
<price>29.99</price>
</book>
</books>
</Bookstore>
<Bookstore id="ID910715717">
<location>bar</location>
<books>
<book category="A" id="1">
<title>Un</title>
<author ref="1">Winkin</author>
<author>Blinkin</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="B" id="10">
<title>Deux</title>
<author>Nod</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="D" id="100">
<title>Trois</title>
<author>Manny</author>
<author>Moe</author>
<year>2005</year>
<price>29.99</price>
</book>
</books>
</Bookstore>
</Catalogue>
我想提取所有作者姓名: 1) location 元素的文本值包含“NY” 2)author 元素不包含“ref”属性；这就是作者标签中不存在 ref 的地方
我最终需要将给定书店内提取的作者连接在一起，以便我生成的数据帧是每个商店一行。我想将书店 ID 保留为数据框中的附加字段，以便我可以唯一地引用每个商店。 由于只有第一家书店位于纽约，因此这个简单示例的结果将类似于:
1 Jane Smith John Doe Karl Pearson William Gosset
如果另一家书店的位置包含“NY”，则它将构成第二行，依此类推。
在这些复杂的条件下，我对 R 解析器的要求是否过高？
最佳答案
require(XML)
xdata <- xmlParse(apptext)
xpathSApply(xdata,'//*/location[text()[contains(.,"NY")]]/following-sibling::books/.//author[not(@ref)]')
#[[1]]
#<author>Jane Smith</author>
#[[2]]
#<author>John Doe</author>
#[[3]]
#<author>Karl Pearson</author>
#[[4]]
#<author>William Gosset</author>
分割:
获取包含“NY”的所有位置
//*/location[text()[contains(.,"NY")]]
获取这些节点的兄弟书籍
/following-sibling::books
从这些注释中获取所有没有 ref 属性的作者
/.//author[not(@ref)]
如果需要文本，请使用 xmlValue:
> xpathSApply(xdata,'//*/location[text()[contains(.,"NY")]]/following-sibling::books/.//author[not(@ref)]',xmlValue)
[1] "Jane Smith" "John Doe" "Karl Pearson" "William Gosset"
更新:
child.nodes <- xpathSApply(xdata,'//*/location[text()[contains(.,"NY")]]/following-sibling::books/.//author[not(@ref)]')
ans.func<-function(x){
xpathSApply(x,'.//ancestor::bookstore[@id]/@id')
}
sapply(child.nodes,ans.func)
# id id id id
#"1" "1" "1" "1"
更新2:
使用更改后的数据
xdata <- '<Catalogue>
<Bookstore id="ID910705541">
<location>foo bar</location>
<books>
<book category="A" id="1">
<title>Alpha</title>
<author ref="1">Matthew</author>
<author>Mark</author>
<author>Luke</author>
<author ref="2">John</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="B" id="10">
<title>Beta</title>
<author ref="1">Huey</author>
<author>Duey</author>
<author>Louie</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="D" id="100">
<title>Gamma</title>
<author ref="1">Tweedle Dee</author>
<author ref="2">Tweedle Dum</author>
<year>2005</year>
<price>29.99</price>
</book>
</books>
</Bookstore>
<Bookstore id="ID910700051">
<location>foo</location>
<books>
<book category="A" id="1">
<title>Happy</title>
<author>Dopey</author>
<author>Bashful</author>
<author>Doc</author>
<author ref="1">Grumpy</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="B" id="10">
<title>Ni</title>
<author ref="1">John</author>
<author ref="2">Paul</author>
<author ref="3">George</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="D" id="100">
<title>San</title>
<author ref="1">Ringo</author>
<year>2005</year>
<price>29.99</price>
</book>
</books>
</Bookstore>
<Bookstore id="ID910715717">
<location>bar</location>
<books>
<book category="A" id="1">
<title>Un</title>
<author ref="1">Winkin</author>
<author>Blinkin</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="B" id="10">
<title>Deux</title>
<author>Nod</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="D" id="100">
<title>Trois</title>
<author>Manny</author>
<author>Moe</author>
<year>2005</year>
<price>29.99</price>
</book>
</books>
</Bookstore>
</Catalogue>'
请注意，以前您有书店，现在有书店。 NY 消失了，所以我使用了 foo
require(XML)
xdata <- xmlParse(xdata)
child.nodes <- getNodeSet(xdata,'//*/location[text()[contains(.,"foo")]]/following-sibling::books/.//author[not(@ref)]')
ans.func<-function(x){
xpathSApply(x,'.//ancestor::Bookstore[@id]/@id')
}
sapply(child.nodes,ans.func)
# id id id id id
#"ID910705541" "ID910705541" "ID910705541" "ID910705541" "ID910700051"
# id id
#"ID910700051" "ID910700051"
xpathSApply(xdata,'//*/location[text()[contains(.,"foo")]]/following-sibling::books/.//author[not(@ref)]',xmlValue)
# [1] "Mark" "Luke" "Duey" "Louie" "Dopey" "Bashful" "Doc"
关于r - 根据相关节点的属性和文本值解析XML，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16238043/