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r - Scrape and Loop with Rvest

问题描述

I have reviewed several answers to similar questions on SO related to this similar topic but neither seem to work for me.

(loop across multiple urls in r with rvest)

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

I have a list of URLs and I wish to grab the table from each and append it to a master dataframe.

## 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
}

The first section works as expect and gets the list of urls I want to scrape. I get the following error:

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

Any suggestions on how to get correct for this error and get the 3 tables looped into a single DF? I appreciate any tips or pointers.

标签： rfor-loopweb-scrapingrvest

解决方案

尝试这个：

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)

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

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