R：在Rvest中使用pipechain命令刮掉多個網址

Question

我有一個包含多個url的chr列表。我想從每個這些網址下載內容'。

爲了避免寫出數以百計的命令，我希望通過使用lapply的循環自動執行該過程。

但是，我的命令返回一個錯誤。是否有可能從多個網址中刪除？

電流接近

長法：工作，但我希望它自動化

urls <-c("https://en.wikipedia.org/wiki/Belarus","https://en.wikipedia.org/wiki/Russia","https://en.wikipedia.org/wiki/England") 

library(rvest) 
library(httr) # required for user_agent command 

uastring <- "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36" 
session <- html_session("https://en.wikipedia.org/wiki/Main_Page", user_agent(uastring)) 
session2<-jump_to(session, "https://en.wikipedia.org/wiki/Belarus") 
session3<-jump_to(session, "https://en.wikipedia.org/wiki/Russia") 
writeBin(session2$response$content, "test1.txt") 
writeBin(session3$response$content, "test2.txt") 

自動/循環：不工作。

urls <-c("https://en.wikipedia.org/wiki/Belarus","https://en.wikipedia.org/wiki/Russia","https://en.wikipedia.org/wiki/England") 

library(rvest) 
library(httr) # required for user_agent command 

uastring <- "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36" 
session <- html_session("https://en.wikipedia.org/wiki/Main_Page", user_agent(uastring)) 
lapply(urls, .%>% jump_to(session)) 
Error: is.session(x) is not TRUE 

摘要

我想下面的兩個過程，jump_to()和writeBin()自動化，如下面的代碼中

session2<-jump_to(session, "https://en.wikipedia.org/wiki/Belarus") 
session3<-jump_to(session, "https://en.wikipedia.org/wiki/Russia") 
writeBin(session2$response$content, "test1.txt") 
writeBin(session3$response$content, "test2.txt") 

Answer 1

你可以做這樣的事情：

urls <-c("https://en.wikipedia.org/wiki/Belarus","https://en.wikipedia.org/wiki/Russia","https://en.wikipedia.org/wiki/England") 
require(httr) 
require(rvest) 
uastring <- "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36" 
session <- html_session("https://en.wikipedia.org/wiki/Main_Page", user_agent(uastring)) 

outfile <- sprintf("%s.html", sub(".*/", "", urls)) 

jump_and_write <- function(x, url, out_file){ 
    tmp = jump_to(x, url) 
    writeBin(tmp$response$content, out_file) 
} 

for(i in seq_along(urls)){ 
    jump_and_write(session, urls[i], outfile[i]) 
}