如何获取某个类之前的HTML元素? [英] How to get HTML element that is before a certain class?

问题描述

我正在抓取并遇到麻烦，使"th"标记的元素出现在另一个包含"type2"类的"th"元素之前.我更喜欢通过在类"type2"的"th"之前确定它是"th"元素，因为我的HTML有很多"th"，这是我在表之间发现的唯一区别.

I'm scraping and having trouble getting the element of the "th" tag that comes before the other "th" element that contains the "type2" class. I prefer to take it by identifying that it is the element "th" before the "th" with class "type2" because my HTML has a lot of "th" and that was the only difference I found between the tables.

使用rvest或xml2(或其他R包)，我可以得到这个父对象吗?我想要的内容是"text_that_I_want".

Using rvest or xml2 (or other R package), can I get this parent? The content which I want is "text_that_I_want".

谢谢！

<tr>
    <th class="array">text_that_I_want</th>
    <td class="array">
        <table>
            <thead>
                <tr>
                    <th class="string type2">name</th>
                    <th class="array type2">answers</th>
                </tr>
            </thead>

推荐答案

相对于给定节点导航xpath的正式且更具通用性的方法是通过 ancestor preceding-sibling :

The formal and more generalizable way to navigate xpath relative to a given node is via ancestor preceding-sibling:

read_html(htmldoc) %>% 
html_nodes(xpath = "//th[@class = 'string type2']/ancestor::td/preceding-sibling::th") %>% 
html_text()
#> [1] "text_that_I_want"

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