web scrape with rvest

问题

I'm trying to grab a table of data using read_html from the r package rvest.

I've tried the below code:

library(rvest)
  raw <- read_html("https://demanda.ree.es/movil/peninsula/demanda/tablas/2016-01-02/2")

I don't believe the above pulled the data from the table, since I see 'raw' is a list of 2:

'node:<externalptr>' and  'doc:<externalptr>'

I've tried grabbing the xpath too:

html_nodes(raw,xpath = '//*[(@id = "tabla_generacion")]//*[contains(concat( " ", @class, " " ), concat( " ", "ng-scope", " " ))]')

Any advice on what to try next?

Thanks.

回答1:

This website is using angular to make a call to get the data. You can just use that call to get the raw JSON. The response is not pure JSON, so you can't just run fromJSON(url), you have to download the data and get rid of the non-JSON stuff before you parse it.

library(jsonlite)
library(httr)
url <- "https://demanda.ree.es/WSvisionaMovilesPeninsulaRest/resources/demandaGeneracionPeninsula?callback=angular.callbacks._2&curva=DEMANDA&fecha=2016-01-02"
a <- GET(url)
a <- content(a, as="text")
# get rid of the non-JSON stuff...
a <- gsub("^angular.callbacks._2\\(", "", a)
a <- gsub("\\);$", "", a)
df <- fromJSON(a, simplifyDataFrame = TRUE)

I found this by pushing F12 in Chrome and looking at the "Sources" tab. The data to fill the table had to come from somewhere... so it's just a matter of figuring out where. I was unable to use rvest to scrape the table. I'm not sure if that call to get the data was executed in R as it was in chrome... so there may have been no data for rvest to scrape.

来源：https://stackoverflow.com/questions/36335498/web-scrape-with-rvest