我正在抓取 http://www.progarchives.com/album.asp?id= 并收到一条警告消息:

Warning message:
XML content does not seem to be XML:
http://www.progarchives.com/album.asp?id=2
http://www.progarchives.com/album.asp?id=3 http://www.progarchives.com/album.asp?id=4
http://www.progarchives.com/album.asp?id=5

抓取器分别对每个页面起作用，但不适用于 url b1=2:b2=1000。

 library(RCurl)
 library(XML)

getUrls <- function(b1,b2){
   root="http://www.progarchives.com/album.asp?id="
   urls <- NULL
     for (bandid in b1:b2){
   urls <- c(urls,(paste(root,bandid,sep="")))
  }
  return(urls)
}

prog.arch.scraper <- function(url){
SOURCE <- getUrls(b1=2,b2=1000)
PARSED <- htmlParse(SOURCE)
album <- xpathSApply(PARSED,"//h1[1]",xmlValue)
date <- xpathSApply(PARSED,"//strong[1]",xmlValue)
band <- xpathSApply(PARSED,"//h2[1]",xmlValue)
return(c(band,album,date))
}

prog.arch.scraper(urls)

最佳答案

这是使用 rvest 和 dplyr 的替代方法:

library(rvest)
library(dplyr)
library(pbapply)

base_url <- "http://www.progarchives.com/album.asp?id=%s"

get_album_info <- function(id) {

  pg <- html(sprintf(base_url, id))
  data.frame(album=pg %>% html_nodes(xpath="//h1[1]") %>% html_text(),
             date=pg %>% html_nodes(xpath="//strong[1]") %>% html_text(),
             band=pg %>% html_nodes(xpath="//h2[1]") %>% html_text(),
             stringsAsFactors=FALSE)

}

albums <- bind_rows(pblapply(2:10, get_album_info))

head(albums)

## Source: local data frame [6 x 3]
## 
##                        album                           date      band
## 1                    FOXTROT Studio Album, released in 1972   Genesis
## 2              NURSERY CRYME Studio Album, released in 1971   Genesis
## 3               GENESIS LIVE         Live, released in 1973   Genesis
## 4        A TRICK OF THE TAIL Studio Album, released in 1976   Genesis
## 5 FROM GENESIS TO REVELATION Studio Album, released in 1969   Genesis
## 6           GRATUITOUS FLASH Studio Album, released in 1984 Abel Ganz

我不想用大量请求来攻击网站，所以提高顺序供您使用。 pblapply 给你一个免费的进度条。

为了善待网站(尤其是因为它没有明确禁止抓取)，您可能需要在 get_album_infoSys.sleep(10)函数。

更新

要处理服务器错误(在本例中为 500，但它也适用于其他错误)，您可以使用 try:

library(rvest)
library(dplyr)
library(pbapply)
library(data.table)

base_url <- "http://www.progarchives.com/album.asp?id=%s"

get_album_info <- function(id) {

  pg <- try(html(sprintf(base_url, id)), silent=TRUE)

  if (inherits(pg, "try-error")) {
    data.frame(album=character(0), date=character(0), band=character(0))
  } else {
    data.frame(album=pg %>% html_nodes(xpath="//h1[1]") %>% html_text(),
               date=pg %>% html_nodes(xpath="//strong[1]") %>% html_text(),
               band=pg %>% html_nodes(xpath="//h2[1]") %>% html_text(),
               stringsAsFactors=FALSE)
  }

}

albums <- rbindlist(pblapply(c(9:10, 23, 28, 29, 30), get_album_info))

##                       album                           date         band
## 1: THE DANGERS OF STRANGERS Studio Album, released in 1988    Abel Ganz
## 2:    THE DEAFENING SILENCE Studio Album, released in 1994    Abel Ganz
## 3:             AD INFINITUM Studio Album, released in 1998 Ad Infinitum

您不会获得错误页面的任何条目(在本例中它只返回 id 9、10 和 30 的条目)。

关于html - 用 R 抓取 .asp 网站，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28933113/