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r - 使用 R 和 rvest 进行网页抓取

问题描述

我有一个项目，我应该从新闻网站上抓取一系列文章。我对新闻的标题和文字感兴趣。在大多数情况下，站点会维护一个基本 URL，例如：

https://www.americanthinker.com /articles/2019/11/why_rich_people_love_poor_immigrants.html https://tmp.americanthinker.com /blog/2015/01/california_begins_giving_drivers_licenses_to_illegal_aliens.html

由于要下载的文章太多（超过1000篇），我想创建一个自动下载所有数据的功能。向量将提供所有网址（每行一个）：

article 
[1] "https://www.americanthinker.com/articles/2019/11/why_rich_people_love_poor_immigrants.html"                   
[2] "https://tmp.americanthinker.com/blog/2015/01/california_begins_giving_drivers_licenses_to_illegal_aliens.html"
[3] "https://www.americanthinker.com/articles/2018/11/immigrants_will_not_fund_our_retirement.html"                
> str(article)
 chr [1:3] "https://www.americanthinker.com/articles/2019/11/why_rich_people_love_poor_immigrants.html" ...
> summary(article)
   Length     Class      Mode 
        3 character character

因此，脚本将使用向量作为地址的来源，并创建一个包含每篇文章的标题和文本的数据框。但是会弹出一些错误。以下是我根据一系列 Stack Overflow 帖子编写的代码：

套餐

library(rvest)
library(purrr)
library(xml2) 
library(dplyr)
library(readr)

导入 CSV 并导出为矢量

base <- read_csv(file.choose(), col_names = FALSE)
article <- pull(base,X1)

第一次尝试

articles_final <- map_df(article, function(i){
  pages<-read_html(article)
  title <-
    article %>%  map_chr(. %>% html_node("h1") %>% html_text())
  content <-
    article %>% map_chr(. %>% html_nodes('.article_body span') %>% html_text() %>% paste(., collapse = ""))
  article_table <- data.frame("Title" = title, "Content" = content)
  return(article_table)
})

第二次尝试

map_df(1:3, function(i){
  page <- read_html(sprintf(article,i))
  data.frame(Title = html_text(html_nodes(page,'.h1')),
             Content= html_text(html_nodes(page,'.article_body span')),
             Site = "American Thinker"
             )
}) -> articles_final

在这两种情况下，我在运行这些函数时都会收到以下错误：

Error in doc_parse_file (con, encoding = encoding, as_html = as_html, options = options):
Expecting a single string value: 
[type = character; extent = 3].

我需要这个来下载和分析文章

非常感谢您的帮助。

编辑

我尝试了下面建议的代码：

I tried and it dod not work, some problem with my coding:
> map_dfc(.x = article,
+         .f = function(x){
+           foo <- tibble(Title = read_html(x) %>%
+                           html_nodes("h1") %>% 
+                           html_text() %>%
+                           .[nchar(.) > 0],
+                         Content = read_html(x) %>% 
+                           html_nodes("p") %>% 
+                           html_text(),
+                         Site = "AmericanThinker")%>%
+             filter(nchar(Content) > 0)
+           }
+         ) -> out
Error: Argument 3 must be length 28, not 46

但是当你看到一个新的错误弹出

标签： rweb-scrapingrvest

解决方案

这是我为你尝试的。我在玩 Selector Gadget 并检查页面源。经过一番检查，我认为您需要使用<title>and <div class="article_body">。该map()部分正在循环浏览三篇文章article并创建一个数据框。每行代表每篇文章。我认为您仍然需要进行一些字符串操作才能获得干净的文本。但这将帮助您抓取所需的内容。

library(tidyverse)
library(rvest)

article <- c("https://www.americanthinker.com/articles/2019/11/why_rich_people_love_poor_immigrants.html",
         "https://tmp.americanthinker.com/blog/2015/01/california_begins_giving_drivers_licenses_to_illegal_aliens.html",
         "https://www.americanthinker.com/articles/2018/11/immigrants_will_not_fund_our_retirement.html")

 map_dfr(.x = article,
         .f = function(x){

                 tibble(Title = read_html(x) %>%
                                html_nodes("title") %>%
                                html_text(),
                        Content = read_html(x) %>%
                                  html_nodes(xpath = "//div[@class='article_body']") %>%
                                  html_text(),
                        Site = "AmericanThinker")}) -> result


#  Title                              Content                                                  Site      
#  <chr>                              <chr>                                                    <chr>     
#1 Why Rich People Love Poor Immigra… "Soon after the Immigration Act of 1965 was passed, rea… AmericanT…
#2 California begins giving driver's… "The largest state in  the union began handing out driv… AmericanT…
#3 Immigrants Will Not Fund Our Reti… "Ask Democrats why they support open borders, and they … AmericanT…

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