需要帮助解释错误：“read_xml.raw”

Question

我正在关注本教程RSelenium and scraping 在我开始测试 navigate_click() 函数之前一切正常。 （set_names 与教程不同，因为我的源网站不同。）

navigate_click <- function() {
  webElem <- remDr$findElement(using = "class name",
                               "google-visualization-table-div-page")

  Sys.sleep(0.5)
  webElem$clickElement()

  remDr$getPageSource()[[1]] %>% 
    read_xml() %>%
    xml_ns_strip() %>%
    xml_find_all(xpath = '//td') %>%
    xml_text() %>%
    set_names(c("PublicationTitle", "County", "Place_of_Publication", "Library")) %>%
    as.list() %>% as_tibble()
}

它返回一个错误：

read_xml.raw(charToRaw(enc2utf8(x)), "UTF-8", ..., as_html = as_html, 中的错误： xmlParseEntityRef: 没有名字 [68]

这是回溯...

> navigate_click()
Error in read_xml.raw(charToRaw(enc2utf8(x)), "UTF-8", ..., as_html = as_html,  : 
  xmlParseEntityRef: no name [68] 
11. read_xml.raw(charToRaw(enc2utf8(x)), "UTF-8", ..., as_html = as_html, 
    options = options) 
10. read_xml.character(.) 
9. read_xml(.) 
8. function_list[[i]](value) 
7. freduce(value, `_function_list`) 
6. `_fseq`(`_lhs`) 
5. eval(quote(`_fseq`(`_lhs`)), env, env) 
4. eval(quote(`_fseq`(`_lhs`)), env, env) 
3. withVisible(eval(quote(`_fseq`(`_lhs`)), env, env)) 
2. remDr$getPageSource()[[1]] %>% read_xml() %>% xml_ns_strip() %>% 
    xml_find_all(xpath = "//td") %>% xml_text() %>% set_names(c("PublicationTitle", 
    "County", "Place_of_Publication", "Library")) %>% as.list() %>% 
    as_tibble() 
1. navigate_click() 

Answer 1

我发现您正在查看的博客有点令人费解；我不清楚 navigate_click 函数是如何工作的，因为它正在获取 HTML 源代码并在其上调用 read_xml()。尽管某些 HTML 页面可能符合严格的 XML 格式，但大多数不是格式良好的 XML。在这些情况下，read_xml 将抛出错误。

幸运的是，xml2 包还有一个read_html 函数，它可以毫无问题地解析您的页面。但是，这不会修复您的函数，因为当您选择 td 元素并获取它们的文本内容时，您会得到一个单一的字符向量，然后您将无法应用 set_names。

无论如何，rvest 包使从已解析的 html 中读取表格变得更加容易。

假设您已经按照您的示例完成了install.packages("rvest") 并创建了remDr，以下应该可以工作：

remDr$navigate("https://view-awesome-table.com/-Lz90gtPDhIyGUzmdMrE/view")
webElem <- remDr$findElement(using = "class name", "google-visualization-table-div-page")
Sys.sleep(0.5)
webElem$clickElement()

remDr$getPageSource()[[1]] %>%
  read_html(x) %>% 
  xml_find_all(xpath = "//*[@class = 'google-visualization-table-table']") %>%
  rvest::html_table() %>%
  `[[`(1) %>%
  `[`(c(1, 2, 3, 7)) %>%
  as_tibble()

#> # A tibble: 15 x 4
#>    PublicationTitle              County    Place_of_Publicati~ Library               
#>    <chr>                         <chr>     <chr>               <chr>                 
#>  1 ALFRETON AND DISTRICT ADVERT~ Derbyshi~ "Alfreton and Ripl~ British Library       
#>  2 ALFRETON AND DISTRICT ADVERT~ Derbyshi~ "Alfreton and Ripl~ Derbyshire: County Ha~
#>  3 ALFRETON AND DISTRICT COMING~ Derbyshi~ "Alfreton"          British Library       
#>  4 ALFRETON AND DISTRICT COMING~ Derbyshi~ "Alfreton"          Derbyshire: County Ha~
#>  5 ALFRETON AND DISTRICT ECHO    Derbyshi~ "Alfreton"          British Library       
#>  6 ALFRETON AND DISTRICT ECHO    Derbyshi~ "Alfreton"          Derbyshire: County Ha~
#>  7 ALFRETON AND RIPLEY ECHO      Derbyshi~ "Chesterfield"      British Library       
#>  8 ALFRETON AND RIPLEY ECHO      Derbyshi~ "Chesterfield"      Derbyshire: Alfreton  
#>  9 ALFRETON ARGUS                Derbyshi~ "Alfreton"          British Library       
#> 10 ALFRETON ARGUS                Derbyshi~ "Alfreton"          Derbyshire: County Ha~
#> 11 ALFRETON JOURNAL              Derbyshi~ ""                  British Library       
#> 12 ALFRETON JOURNAL              Derbyshi~ ""                  Derbyshire: Alfreton  
#> 13 ALFRETON JOURNAL              Derbyshi~ ""                  Derbyshire: County Ha~
#> 14 ALFRETON JOURNAL              Derbyshi~ ""                  Derbyshire: Magic Att~
#> 15 ALFRETON TRADER               Derbyshi~ ""                  British Library