r - 通过循环 rvest::follow_link() 函数来抓取链接的 HTML 网页

Question

如何循环该rvest::follow_link()功能以抓取链接的网页？

用例：

1. 识别所有乐高电影演员
2. 关注所有乐高电影演员链接
3. 为所有演员获取每部电影（+ 年）的表格

我需要的所需选择器如下：

library(rvest)
lego_movie <- html("http://www.imdb.com/title/tt1490017/")
lego_movie <- lego_movie %>%
  html_nodes(".itemprop , .character a") %>%
  html_text()

# follow cast links
(".itemprop .itemprop") 

# grab tables of all movies and dates for each cast member
(".year_column , b a")

期望的输出：

castMember       movie    year
Will Arnett      Lego     2017
Will Arnett      BoJack   2014
Will Arnett      Wander   2014
        ............
Elizabeth Banks  Moonbeam 2015
Elizabeth Banks  Wet Hot  2015
        ............
Alison Brie      Get Hard 2015
Alison Brie      GetaJob  2015
        .....etc.....

Answer 1

也许这样的事情可以奏效。

library(rvest)
library(stringr)
library(data.table)
lego_movie <- read_html("http://www.imdb.com/title/tt1490017/")
cast <- lego_movie %>%
    html_nodes("#titleCast .itemprop span") %>%
    html_text()
cast

s <- html_session("http://www.imdb.com/title/tt1490017/")

cast_movies <- list()

for(i in cast[1:3]){
    actorpage <- s %>% follow_link(i) %>% read_html()
    cast_movies[[i]]$movies <-  actorpage %>% 
        html_nodes("b a") %>% html_text() %>% head(10)
    cast_movies[[i]]$years <- actorpage %>%
        html_nodes("#filmography .year_column") %>% html_text() %>% 
        head(10) %>% str_extract("[0-9]{4}")
    cast_movies[[i]]$name <- rep(i, length(cast_movies[[i]]$years))
}

cast_movies
as.data.frame(cast_movies[[1]])
rbindlist(cast_movies)

Answer 2

这是未经测试的，所以它可能是错误的。我会一步一步地检查它并验证它是否正确。我不确定如何在这种情况下使用 follow_link ......但这就是我想出的......

library("rvest")
library("stringr")
lego_movie <- html("http://www.imdb.com/title/tt1490017/")
links <- lego_movie %>%
            html() %>%
            html_nodes(".itemprop , a") %>% xml_attr("href")
links[is.na(links)] <- ""

actors <- lego_movie %>%
  html() %>%
  html_nodes(".itemprop , a") %>%
html_text()

df <- data.frame(name=actors, link=links, stringsAsFactors=F)
df <- subset(df, substring(link, 2, 5)=="name")
df <- subset(df, name!="")
df$name <- gsub("\\n", "", df$name)
df$name <- str_trim(df$name)
df <- df[order(df$name),]
df <- subset(df, !duplicated(df$name))

get_movies <- function(name, link){
  url <- paste0("http://www.imdb.com", link)
  movies <- url %>%
    html() %>%
    html_nodes(".year_column , b a") %>%
    html_text()
  # take care of random date at top of some actors stuff...
  if(length(movies)%%2==1){movies <- movies[-1]}
  movies <- gsub("\\n", "", movies)
  movies <- str_trim(movies)
  df <- data.frame(date=movies[seq(1, length(movies), 2)], 
                   movie=movies[seq(2, length(movies), 2)],
                   stringsAsFactors=F)
  df <- cbind(name=rep(name, nrow(df)), df)
  return(df)
}

final_df <- data.frame()
for(i in 1:nrow(df)){
  final_df <- rbind(final_df, get_movies(df$name[i], df$link[i]))
}