使用rvest

Question

刮HTML表跨度我使用rvest提取如下頁表所示：

https://en.wikipedia.org/wiki/List_of_United_States_presidential_elections_by_popular_vote_margin

下面的代碼工作：

URL <- 'https://en.wikipedia.org/wiki/List_of_United_States_presidential_elections_by_popular_vote_margin' 
table <- URL %>% 
    read_html %>% 
    html_nodes("table") %>% 
    .[[2]] %>% 
    html_table(trim=TRUE) 

但利潤率列總統的名字有一些奇怪的價值。其原因是源代碼有以下幾點：

<td><span style="display:none">00.001</span>−10.44%</td> 

這樣反而讓-10.44％我得到00.001â'10.44％

我怎麼能解決這個問題？

Answer 1

一種選擇是單獨定位並替換問題列。

保證金欄能夠與xpath

# get the html 
html <- URL %>% 
    read_html() 

# Example using the first margin column (column # 6) 
html %>% 
    html_nodes(xpath = '//table[2]') %>%  # get table 2 
    html_nodes(xpath = '//td[6]/text()') %>% # get column 6 using text() 
    iconv("UTF-8", "UTF-8")     # to convert "−" to "-" 
# [1] "−10.44%" "−3.00%" "−0.83%" "−0.51%" "0.09%" "0.17%" "0.57%" 
# [8] "0.70%" "1.45%" "2.06%" "2.46%" "3.01%" "3.12%" "3.86%" 
#[15] "4.31%" "4.48%" "4.79%" "5.32%" "5.56%" "6.05%" "6.12%" 
#[22] "6.95%" "7.27%" "7.50%" "7.72%" "8.51%" "8.53%" "9.74%" 
#[29] "9.96%" "10.08%" "10.13%" "10.85%" "11.80%" "12.20%" "12.25%" 
#[36] "14.20%" "14.44%" "15.40%" "17.41%" "17.76%" "17.81%" "18.21%" 
#[43] "18.83%" "22.58%" "23.15%" "24.26%" "25.22%" "26.17%" 

有針對性做其他保證金列相同。我使用iconv將−轉換爲-，因爲這是一個編碼問題，但您可以使用基於替換的解決方案（例如使用sub）。

要與美國總統的名字目標列，您可以再次使用XPath：

html %>% 
    html_nodes(xpath = '//table[2]') %>% 
    html_nodes(xpath = '//td[3]/a/text()') %>% 
    html_text() 
# [1] "John Quincy Adams"  "Rutherford Hayes"  "Benjamin Harrison"  
# [4] "George W. Bush"   "James Garfield"   "John Kennedy"   
# [7] "Grover Cleveland"  "Richard Nixon"   "James Polk"    
#[10] "Jimmy Carter"   "George W. Bush"   "Grover Cleveland"  
#[13] "Woodrow Wilson"   "Barack Obama"   "William McKinley"  
#[16] "Harry Truman"   "Zachary Taylor"   "Ulysses Grant"   
#[19] "Bill Clinton"   "William Henry Harrison" "William McKinley"  
#[22] "Franklin Pierce"  "Barack Obama"   "Franklin Roosevelt"  
#[25] "George H. W. Bush"  "Bill Clinton"   "William Taft"   
#[28] "Ronald Reagan"   "Franklin Roosevelt"  "Abraham Lincoln"  
#[31] "Abraham Lincoln"  "Dwight Eisenhower"  "Ulysses Grant"   
#[34] "James Buchanan"   "Andrew Jackson"   "Martin Van Buren"  
#[37] "Woodrow Wilson"   "Dwight Eisenhower"  "Herbert Hoover"   
#[40] "Franklin Roosevelt"  "Andrew Jackson"   "Ronald Reagan"   
#[43] "Theodore Roosevelt"  "Lyndon Johnson"   "Richard Nixon"   
#[46] "Franklin Roosevelt"  "Calvin Coolidge"  "Warren Harding"