从html表中抓取数据

Question

我正在尝试使用rvest包从CABI入侵物种纲要中提取入侵植物物种位置的数据.

看了几个教程,我发现我应该能够很容易地从表中抓取数据.但是,我一直遇到困难.

假设我想要品种Brassica tournefortii的位置数据.我应该能够使用此代码,该代码使用此处概述的技术来获取物种记录位置的详细信息.

 library(rvest)
 isc<-read_html("http://www.cabi.org/isc/datasheet/50069")
 isc %>% 
 html_node("#toDistributionTable td:nth-child(1)") %>%
 html_text()

但是,运行此代码我收到错误

Error: No matches

我是webscraping的新手.我做错了什么吗？

Answer 1

首先,我希望我能更多地投资你.最后一个刮刮问题不是$ SPORTSBALL或$ MONEY相关!:-)

那个网站很邪恶.它使用需要处理的嵌入式命名空间,这也意味着使用xml2包:

library(rvest)
library(xml2)

isc <- read_html("http://www.cabi.org/isc/datasheet/50069")

ns <- xml_ns(isc)

xml_text(xml_find_all(isc, xpath="//div[@id='toDistributionTable']/table/tbody/tr/td[1]", ns))

##  [1] "ASIA"                           "Azerbaijan"                    
##  [3] "Bhutan"                         "China"                         
##  [5] "-Tibet"                         "India"                         
##  [7] "-Delhi"                         "-Indian Punjab"                
##  [9] "-Rajasthan"                     "-Uttar Pradesh"                
## [11] "Iran"                           "Iraq"                          
## [13] "Israel"                         "Jordan"                        
## [15] "Kuwait"                         "Lebanon"                       
## [17] "Oman"                           "Pakistan"                      
## [19] "Qatar"                          "Saudi Arabia"                  
## [21] "Syria"                          "Turkey"                        
## [23] "Turkmenistan"                   "United Arab Emirates"          
## [25] "Uzbekistan"                     "Yemen"                         
## [27] "AFRICA"                         "Algeria"                       
## [29] "Egypt"                          "Libya"                         
## [31] "Morocco"                        "South Africa"                  
## [33] "Tunisia"                        "NORTH AMERICA"                 
## [35] "Mexico"                         "USA"                           
## [37] "-Arizona"                       "-California"                   
## [39] "-Nevada"                        "-New Mexico"                   
## [41] "-Texas"                         "-Utah"                         
## [43] "SOUTH AMERICA"                  "Chile"                         
## [45] "EUROPE"                         "Belgium"                       
## [47] "Cyprus"                         "Denmark"                       
## [49] "France"                         "Greece"                        
## [51] "Ireland"                        "Italy"                         
## [53] "Spain"                          "Sweden"                        
## [55] "UK"                             "-England and Wales"            
## [57] "-Scotland"                      "OCEANIA"                       
## [59] "Australia"                      "-Australian Northern Territory"
## [61] "-New South Wales"               "-Queensland"                   
## [63] "-South Australia"               "-Tasmania"                     
## [65] "-Victoria"                      "-Western Australia"            
## [67] "New Zealand"