[英]rvest HTML table scraping techniques return empty lists
I have had success with rvest
when scraping data from html tables, however, for this particular website, http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/ , when I run the code 我在从html表中抓取数据时获得了
rvest
成功,但是,对于这个特定的网站, http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/ ,当我运行代码时
url <- "http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/"
rankings <- url %>%
read_html %>%
html_nodes("table") %>%
html_table()
All that is returned is an empty list. 返回的所有内容都是一个空列表。 What might be wrong?
可能有什么问题?
The "problem" with this site is that it dynamically loads a javascript file which it then executes via a callback mechanism to create the JS data which it then builds the tables/vis from. 这个站点的“问题”是它动态加载一个javascript文件,然后通过回调机制执行该文件以创建JS数据,然后从中构建表/ vis。
One way to get the data is [R]Selenium, but that's problematic for many folks. 获取数据的一种方法是[R] Selenium,但这对许多人来说都是个问题。
Another way is to use the Developer Tools of your browser to see the JS request, run "Copy as cURL" (right-click, usually) and then use some R-fu to get what you need. 另一种方法是使用浏览器的开发人员工具查看JS请求,运行“复制为cURL”(通常右键单击),然后使用一些R-fu来获取所需内容。 Since this is going to be returning javascript, we'll need to do some mangling before ultimately converting the JSON.
由于这将返回javascript,我们需要在最终转换JSON之前进行一些修改。
library(jsonlite)
library(curlconverter)
library(httr)
# this is the `Copy as cURL` result, but you can leave it in your clipboard
# and not do this in production. Read the `curlconverter` help for more info
CURL <- "curl 'http://omo.akamai.opta.net/competition.php?feed_type=ru3&competition=205&season_id=2016&user=USERNAME&psw=PASSWORD&jsoncallback=RU3_205_2016' -H 'DNT: 1' -H 'Accept-Encoding: gzip, deflate, sdch' -H 'Accept-Language: en-US,en;q=0.8' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.94 Safari/537.36 Vivaldi/1.1.453.54' -H 'Accept: */*' -H 'Referer: http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/' -H 'Connection: keep-alive' -H 'If-Modified-Since: Wed, 11 May 2016 14:47:09 GMT' -H 'Cache-Control: max-age=0' --compressed"
req <- make_req(straighten(CURL))[[1]]
req
# that makes:
# httr::VERB(verb = "GET", url = "http://omo.akamai.opta.net/competition.php?feed_type=ru3&competition=205&season_id=2016&user=USERNAME&psw=PASSWORD&jsoncallback=RU3_205_2016",
# httr::add_headers(DNT = "1", `Accept-Encoding` = "gzip, deflate, sdch",
# `Accept-Language` = "en-US,en;q=0.8", `User-Agent` = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.94 Safari/537.36 Vivaldi/1.1.453.54",
# Accept = "*/*", Referer = "http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/",
# Connection = "keep-alive", `If-Modified-Since` = "Wed, 11 May 2016 14:47:09 GMT",
# `Cache-Control` = "max-age=0"))
# which we can transform into the following after experimenting
URL <- "http://omo.akamai.opta.net/competition.php?feed_type=ru3&competition=205&season_id=2016&user=USERNAME&psw=PASSWORD&jsoncallback=RU3_205_2016"
pg <- GET(URL,
add_headers(
`User-Agent` = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.94 Safari/537.36 Vivaldi/1.1.453.54",
Referer = "http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/"))
# now all we need to do is remove the callback
dat_from_json <- fromJSON(gsub(")$", "", gsub("^RU3_205_2016\\(", "", content(pg, as="text"))), flatten=FALSE)
# we can also try removing the JSON callback, but it will return XML instead of JSON,
# which is fine since we can parse that easily
URL <- "http://omo.akamai.opta.net/competition.php?feed_type=ru3&competition=205&season_id=2016&user=USERNAME&psw=PASSWORD"
pg <- GET(URL,
add_headers(
`User-Agent` = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.94 Safari/537.36 Vivaldi/1.1.453.54",
Referer = "http://www.sanzarrugby.com/superrugby/competition-stats/2016-team-ranking/"))
xml_doc <- content(pg, as="parsed", encoding="UTF-8")
# but then you have to transform the XML, which I'll leave as an exercise to the OP :-)
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