本文介绍了如何使用 xmlValue 制作长度节点的 xpathSApply 输出向量?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
假设我有以下内容:
library(XML)
my.xml <- '
<tv>
<show>
<name>Star Trek TNG</name>
<rating>1.0</rating>
</show>
<show>
<name>Doctor Who</name>
</show>
<show>
<name>Babylon 5</name>
<rating>2.0</rating>
</show>
</tv>
'
doc <- xmlParse(my.xml)
xpathSApply(doc, "/tv/show/rating", xmlValue)
# [1] "1.0" "2.0"
有三个显示"节点.我怎样才能使输出成为:
There are three 'show' nodes. How can I instead make the output be:
# [1] "1.0" NULL "2.0"
为了解释Doctor Who在xml中没有评级但长度仍然是3?
so as to account for Doctor Who not having a rating in the xml but the length still being 3?
推荐答案
如果您提供一直到 'rating' 的路径,节点列表将已经只有 2 个元素开始.因此,当您将 xmlValue()
应用于此节点列表时,输出也将只有 2 个元素.您可以通过从树中的上一层开始来解决这个问题:
If you supply the path all the way to 'rating', the node list will already only have the 2 elements to begin with. So when you apply xmlValue()
to this node list, the output will also only have 2 elements. You can get around this by just starting from one level up in the tree:
> xpathSApply(doc, '/tv/show', function(x) xmlValue(xmlChildren(x)$rating))
[1] "1.0" NA "2.0"
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