使用rvest(R)进行网络抓取时停止使用网址

Question

我已经构建了一个功能,它可以获取网址并在抓取网页后返回所需的结果.功能如下:

library(httr) 
library(curl) 
library(rvest) 
library(dplyr)

sd_cat <- function(url){
  cat <- curl(url, handle = new_handle("useragent" = "myua")) %>%
  read_html() %>%
  html_nodes("#breadCrumbWrapper") %>%
  html_text()

x <- cat[1]

#y <- gsub(pattern = "\n", x=x, replacement = " ")

y <- gsub(pattern = "\t", x=x, replacement = " ")

y <- gsub("\\d|,|\t", x=y, replacement = "")

y <- gsub("^ *|(?<= ) | *$", "", y, perl=T)

z <- gsub("\n*{2,}","",y)

z <- gsub(" {2,}",">",z)

final <- substring(z,2)

final <- substring(final,1,nchar(final)-1)

final

#sample discontinued url: "http://www.snapdeal.com//product/givenchy-xeryus-rouge-g-edt/1978028261"
#sample working url: "http://www.snapdeal.com//product/davidoff-cool-water-game-100ml/1339014133"
}

这个函数在包含多个url的字符向量上使用sapply工作正常,但如果停止使用单个url,则该函数抛出

open.connection(x,"rb")出错:HTTP错误404.

我需要一种方法来跳过已停止的URL以使该功能正常工作.

Answer 1

更好的解决方案是使用httr并在响应不正确时故意采取措施:

library(httr) 
library(rvest) 

sd_cat <- function(url){
  r <- GET(url, user_agent("myua"))
  if (status_code(r) >= 300)
    return(NA_character_)

  r %>%
    read_html() %>%
    html_nodes("#breadCrumbWrapper") %>%
    .[[1]] %>% 
    html_nodes("span") %>% 
    html_text()
}

sd_cat("http://www.snapdeal.com//product/givenchy-xeryus-rouge-g-edt/1978028261")
sd_cat("http://www.snapdeal.com//product/davidoff-cool-water-game-100ml/1339014133")

(我也用更好的rvest替换你的正则表达式)