r - 使用 rvest (R) 进行网络抓取时停止使用 url

Question

我构建了一个函数，它接受一个 url 并在抓取网页后返回所需的结果。函数如下:

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"
}

此函数在包含多个 url 的字符向量上使用 sapply 时效果很好，但如果单个 url 中断，则该函数会抛出

Error in open.connection(x, "rb") : HTTP error 404.

我需要一种方法来跳过已停用的网址，以使该功能正常工作。

Answer 1

更好的解决方案是使用 httr 并在响应不正确时有意采取措施:

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")

(我还用更好地使用 rvest 替换了你的正则表达式)