Rvest刮圈

Question

我已经回顾了几个类似问题的答案，这些问题都与这个相似的主题有关，但似乎都不适合我。

(loop across multiple urls in r with rvest)

(Harvest (rvest) multiple HTML pages from a list of urls)

我有一个URL列表，我希望从每个URL中获取该表，并将其附加到主数据框架中。

## get all urls into one list
page<- (0:2)
urls <- list()
for (i in 1:length(page)) {
  url<- paste0("https://www.mlssoccer.com/stats/season?page=",page[i])
  urls[[i]] <- url
}


### loop over the urls and get the table from each page
table<- data.frame()
for (j in urls) {
  tbl<- urls[j] %>% 
    read_html() %>% 
    html_node("table") %>%
    html_table()
  table[[j]] <- tbl
}

第一部分以expect的方式工作，并获取我想要抓取的urls列表。我得到以下错误：

 Error in UseMethod("read_xml") : 
  no applicable method for 'read_xml' applied to an object of class "list"

对于如何纠正这个错误并将3个表环成一个DF，有什么建议吗？我很感激你的任何建议。

Answer 1

试试这个：

library(tidyverse)
library(rvest)

page<- (0:2)
urls <- list()
for (i in 1:length(page)) {
  url<- paste0("https://www.mlssoccer.com/stats/season?page=",page[i])
  urls[[i]] <- url
}

### loop over the urls and get the table from each page
tbl <- list()
j <- 1
for (j in seq_along(urls)) {
  tbl[[j]] <- urls[[j]] %>%   # tbl[[j]] assigns each table from your urls as an element in the tbl list
    read_html() %>% 
    html_node("table") %>%
    html_table()
  j <- j+1                    # j <- j+1 iterates over each url in turn and assigns the table from the second url as an element of tbl list, [[2]] in this case
}

#convert list to data frame
tbl <- do.call(rbind, tbl)

在原始代码中for循环末尾的table[[j]] <- tbl是不必要的，因为我们在这里将每个url分配为tbl列表的一个元素：tbl[[j]] <- urls[[j]]

Answer 2

这是你的问题：

for (j in urls) {
  tbl<- urls[j] %>% 

使用j in urls时，j值不是整数，而是urls本身。

尝试：

for (j in 1:length(urls)) {
  tbl<- urls[[j]] %>% 
    read_html() %>% 
    html_node("table") %>%
    html_table()
  table[[j]] <- tbl
}

您也可以使用seq_along()

for (j in seq_along(urls))