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Html 使用R-can'；无法访问某些节点

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Html 使用R-can'；无法访问某些节点,html,r,web-scraping,rvest,Html,R,Web Scraping,Rvest,我在网上有大量取水许可证，我想从中提取一些数据。比如说 url <- "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1" 或使用css选择器： url %>% read_html() %>% html_nodes(css = "#main") %>% html_nodes(css = "div") %>% html_nodes(css = "h1") %>

我在网上有大量取水许可证，我想从中提取一些数据。比如说

url <- "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1"
或使用css选择器：

url %>% 
read_html() %>% 
html_nodes(css = "#main") %>% 
html_nodes(css = "div") %>% 
html_nodes(css = "h1") %>% 
html_text()
[1] "Details for CRC000002.1"
到目前为止，一切都很好，但我真正想要的信息被埋藏得更深了，我似乎无法找到它。例如，客户端名称字段（“在本例中为Killermont Station Limited”）具有以下xpath：

clientxpath <- '//*[@id="main"]/div/div[1]/div/table/tbody/tr[1]/td[2]'
url %>% 
read_html() %>% 
html_nodes(xpath = clientxpath) %>%
html_text()
character(0)
但是它没有给我任何关于在xpath中使用替代前缀的线索（如果我知道html，这可能很明显）

我的朋友指出，一些文档是用javascript（ajax）编写的，这可能也是问题的一部分。也就是说，上面我想说的内容显示在html中，但它位于一个名为“div.ajax-block”的节点中

css selectors: #main > div > div.ajax-block > div > table > tbody > tr:nth-child(1) > td:nth-child(4)
有人能帮忙吗？谢谢

非常令人不安的是，大多数（如果不是全部的话）SoR贡献者在抓取时默认在简短的“答案”中“使用重量级的第三方依赖关系”。99%的时间你不需要硒。你只需要锻炼一下小的灰色细胞

首先，页面异步加载内容的一个重要线索是出现的等待微调器。第二个是在您的代码片段中，
div
实际上有一部分选择器名称，其中包含
ajax
。XHR请求正在发挥作用的信号装置

如果在浏览器中打开“开发人员工具”并重新加载页面，然后转到“网络”，然后单击“XHR”选项卡，您将看到：

页面上的大多数“真实”数据都是动态加载的。我们可以编写模仿浏览器调用的
httr
调用

然而

我们首先需要对主页进行一次
GET
调用，为我们提供一些cookie，然后找到一个用于防止网站被滥用的每生成会话令牌。它是使用JavaScript定义的，因此我们将使用
V8
包对其进行评估。我们可以使用正则表达式来查找字符串。做你喜欢做的事

library(httr)
library(rvest)
library(dplyr)
library(V8)

ctx <- v8() # we need this to eval some javascript

# Prime Cookies -----------------------------------------------------------

res <- httr::GET("https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1")

httr::cookies(res)
##          domain flag path secure          expiration                 name
## 1 .ecan.govt.nz TRUE    /  FALSE 2019-11-24 11:46:13   visid_incap_927063
## 2 .ecan.govt.nz TRUE    /  FALSE                <NA> incap_ses_148_927063
##                                                              value
## 1 +p8XAM6uReGmEnVIdnaxoxWL+VsAAAAAQUIPAAAAAABjdOjQDbXt7PG3tpBpELha
## 2         nXJSYz8zbCRj8tGhzNANAhaL+VsAAAAA7JyOH7Gu4qeIb6KKk/iSYQ==
pg <- httr::content(res)

html_node(pg, xpath=".//script[contains(., '_monsido')]") %>%
  html_text() %>%
  ctx$eval()
## [1] "2"
monsido_token <- ctx$get("_monsido")[1,2]
以下是“同意概述”部分：

以下是“同意条件”：

httr:：GET(
url=”https://www.ecan.govt.nz/data/consent-search/consentconditions/CRC000002.1",
httr：：添加_头(
Referer=”https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
Authority=“www.ecan.govt.nz”，
`X-request-With`=“XMLHttpRequest”
),
httr:：set_cookies(
monsido=monsido_代币
)
)->res
httr:：含量（分辨率）%>%
as.character（）%>%
子串（1300）%
猫（）
## 
## 
##
    
##
  • 
##           
##             
##1
以下是“同意相关”：

httr:：GET(
url=”https://www.ecan.govt.nz/data/consent-search/consentrelated/CRC000002.1",
httr：：添加_头(
Referer=”https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
Authority=“www.ecan.govt.nz”，
`X-request-With`=“XMLHttpRequest”
),
httr:：set_cookies(
monsido=monsido_代币
)
)->res
httr:：含量（分辨率）%>%
as.character（）%>%
子串（1300）%
猫（）
## 
## 
##没有相关文件

## 
## 
## 
## 
##   
##     
##       
## 
##关系
##记录
以下是“工作流程：

httr::GET(
  url = "https://www.ecan.govt.nz/data/consent-search/consentworkflow/CRC000002.1",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    Authority = "www.ecan.govt.nz",
    `X-Requested-With` = "XMLHttpRequest"
  ),
  httr::set_cookies(
    monsido = monsido_token
  )
) -> res

httr::content(res)
## {xml_document}
## <html>
## [1] <body><p>No workflow</p></body>

httr:：GET(
url=”https://www.ecan.govt.nz/data/consent-search/consentworkflow/CRC000002.1",
httr：：添加_头(
Referer=”https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
Authority=“www.ecan.govt.nz”，
`X-request-With`=“XMLHttpRequest”
),
httr:：set_cookies(
monsido=monsido_代币
)
)->res
httr：：内容（res）
##{xml_文档}
## 
##[1]没有工作流
以下是“同意流限制”：

httr:：GET(
url=”https://www.ecan.govt.nz/data/consent-search/consentflowrestrictions/CRC000002.1",
httr：：添加_头(
Referer=”https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
Authority=“www.ecan.govt.nz”，
`X-request-With`=“XMLHttpRequest”
),
httr:：set_cookies(
monsido=monsido_代币
)
)->res
httr:：含量（分辨率）%>%
as.character（）%>%
子串（1300）%
猫（）
## 
## 
##     
## 
##低流量场地
##今日流量（m3/s）
##
您仍然需要解析HTML，但现在您只需使用普通的R包即可完成所有工作。

首先，您从该页面获取数据是否合法？是的，这都是公共信息。它是动态页面，使用Selenium。您将如何在RSelenium中提取数据？我快速查看了一下，似乎非常复杂！请查看我的答案。这“使用硒”“疯狂就是疯狂。谢谢，太棒了！工作非常完美，现在我开始用文本模式匹配将我的头撞到墙上。你能简单地解释一下如何选择GET的参数吗？在这种情况下，它们工作得很好，但我不认为我可以复制它，而且R中的帮助文件有点不透明。如果这不是时间敏感的，请让我明天把它放到GitHub中，我会在这里删除一个链接，我们可以解决GitHub的问题。酷。如果你能把你对这个答案的最初评论作为一个问题写在我的文章里，我会在明天写一个便条。今晚是我大学一年级儿子回家过感恩节的最后一晚，所以我明天就可以满怀热情地开始了。 
library(httr)
library(rvest)
library(dplyr)
library(V8)

ctx <- v8() # we need this to eval some javascript

# Prime Cookies -----------------------------------------------------------

res <- httr::GET("https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1")

httr::cookies(res)
##          domain flag path secure          expiration                 name
## 1 .ecan.govt.nz TRUE    /  FALSE 2019-11-24 11:46:13   visid_incap_927063
## 2 .ecan.govt.nz TRUE    /  FALSE                <NA> incap_ses_148_927063
##                                                              value
## 1 +p8XAM6uReGmEnVIdnaxoxWL+VsAAAAAQUIPAAAAAABjdOjQDbXt7PG3tpBpELha
## 2         nXJSYz8zbCRj8tGhzNANAhaL+VsAAAAA7JyOH7Gu4qeIb6KKk/iSYQ==
pg <- httr::content(res)

html_node(pg, xpath=".//script[contains(., '_monsido')]") %>%
  html_text() %>%
  ctx$eval()
## [1] "2"
monsido_token <- ctx$get("_monsido")[1,2]

httr::VERB(
  verb = "POST", url = "https://www.ecan.govt.nz/data/document-library/searchlist",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    `X-Requested-With` = "XMLHttpRequest",
    TE = "Trailers"
  ), httr::set_cookies(
    monsido = monsido_token
  ),
  body = list(
    name = "CRC000002.1",
    pageSize = "999999"
  ),
  encode = "form"
) -> res

httr::content(res)
## NULL ## <<=== this is OK as there is no response

httr::GET(
  url = "https://www.ecan.govt.nz/data/consent-search/consentoverview/CRC000002.1",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    Authority = "www.ecan.govt.nz",
    `X-Requested-With` = "XMLHttpRequest"
  ),
  httr::set_cookies(
    monsido = monsido_token
  )
) -> res

httr::content(res) %>%
  html_table() %>%
  glimpse()
## List of 1
##  $ :'data.frame':    5 obs. of  4 variables:
##   ..$ X1: chr [1:5] "RMA Authorisation Number" "Consent Location" "To" "Commencement Date" ...
##   ..$ X2: chr [1:5] "CRC000002.1" "Manuka Creek, KILLERMONT STATION" "To take water from Manuka Creek at or about map reference NZMS 260 H39:5588-2366 for irrigation of up to 40.8 hectares." "29 Apr 2010" ...
##   ..$ X3: chr [1:5] "Client Name" "State" "To take water from Manuka Creek at or about map reference NZMS 260 H39:5588-2366 for irrigation of up to 40.8 hectares." "29 Apr 2010" ...
##   ..$ X4: chr [1:5] "Killermont Station Limited" "Issued - Active" "To take water from Manuka Creek at or about map reference NZMS 260 H39:5588-2366 for irrigation of up to 40.8 hectares." "29 Apr 2010" ...

httr::GET(
  url = "https://www.ecan.govt.nz/data/consent-search/consentconditions/CRC000002.1",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    Authority = "www.ecan.govt.nz",
    `X-Requested-With` = "XMLHttpRequest"
  ),
  httr::set_cookies(
    monsido = monsido_token
  )
) -> res

httr::content(res) %>%
  as.character() %>%
  substring(1, 300) %>%
  cat()
## <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
## <html><body><div class="consentDetails">
##     <ul class="unstyled-list">
## <li>
##           
##             
##             <strong class="pull-left">1</strong> <div class="pad-left1">The rate at which wa

httr::GET(
  url = "https://www.ecan.govt.nz/data/consent-search/consentrelated/CRC000002.1",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    Authority = "www.ecan.govt.nz",
    `X-Requested-With` = "XMLHttpRequest"
  ),
  httr::set_cookies(
    monsido = monsido_token
  )
) -> res

httr::content(res) %>%
  as.character() %>%
  substring(1, 300) %>%
  cat()
## <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
## <html><body>
## <p>There are no related documents.</p>
## 
## 
## 
## 
##   
##     <div class="summary-table-wrapper">
##       <table class="summary-table left">
## <thead><tr>
## <th>Relationship</th>
##           <th>Recor

httr::GET(
  url = "https://www.ecan.govt.nz/data/consent-search/consentworkflow/CRC000002.1",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    Authority = "www.ecan.govt.nz",
    `X-Requested-With` = "XMLHttpRequest"
  ),
  httr::set_cookies(
    monsido = monsido_token
  )
) -> res

httr::content(res)
## {xml_document}
## <html>
## [1] <body><p>No workflow</p></body>

httr::GET(
  url = "https://www.ecan.govt.nz/data/consent-search/consentflowrestrictions/CRC000002.1",
  httr::add_headers(
    Referer = "https://www.ecan.govt.nz/data/consent-search/consentdetails/CRC000002.1",
    Authority = "www.ecan.govt.nz",
    `X-Requested-With` = "XMLHttpRequest"
  ),
  httr::set_cookies(
    monsido = monsido_token
  )
) -> res

httr::content(res) %>%
  as.character() %>%
  substring(1, 300) %>%
  cat()
## <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
## <html><body><div class="summary-table-wrapper">
##     <table class="summary-table left">
## <thead>
## <th colspan="2">Low Flow Site</th>
##       <th>Todays Flow <span class="lower">(m3/s)</span>
## </th>