提问人：Jelo A 提问时间：10/14/2020 更新时间：10/14/2020 访问量：143
从 R 中的 HTML 节点列表中提取以 .pdf 结尾的 URL
extracting url ending in .pdf from a list of html nodes in R
问：
我有一个 url 列表，每个 url 都包含一个指向 pdf 文档的 url。我想使用 R 提取并下载 pdf 文档。这是我到目前为止的代码：
从 reliefweb.int 下载数据
#get all the results for the Afghanistan HNO search
result <- GET("https://api.reliefweb.int/v1/reports?appname=rwint-user-0&profile=list&preset=latest&slim=1&query[value]=(primary_country.iso3%3A%22afg%22)%20AND%20ocha_product%3A%22Humanitarian%20Needs%20Overview%22%20AND%20source%3A%22UN%20Office%20for%20the%20Coordination%20of%20Humanitarian%20Affairs%22&query[operator]=AND")
#create a list of all the urls listed in the search page
rawToChar(result$content)
result2<- fromJSON(rawToChar(result$content))
urllist<- result2[["data"]][["fields"]][["url"]]
#Extraxt links to the pdf docs
urlpdf<- lapply(urllist,read_html)
有了这段代码，我有一个html节点列表，但我坚持如何从中提取.pdf url。知道我该如何进行，或者是否有更有效的方法可以做到这一点吗？
答：
0赞
Allan Cameron
10/14/2020
#1
您似乎正在使用 ，因此您可以执行以下操作：rvest
library(httr)
library(rvest)
library(jsonlite)
result2<- fromJSON(rawToChar(result$content))
urllist<- result2[["data"]][["fields"]][["url"]]
urlpdf<- lapply(urllist, read_html)
links <- lapply(urlpdf, function(x) html_attr(html_nodes(x, xpath = "//a"), "href"))
pdfs <- lapply(links, function(x) grep("\\.pdf$", x, value = TRUE))
其结果是：
pdfs
#> [[1]]
#> [1] "https://reliefweb.int/sites/reliefweb.int/files/resources/afg_humanitarian_needs_overview_2020.pdf"
#>
#> [[2]]
#> [1] "https://reliefweb.int/sites/reliefweb.int/files/resources/afg_2019_humanitarian_needs_overview.pdf"
#>
#> [[3]]
#> [1] "https://reliefweb.int/sites/reliefweb.int/files/resources/afg_2018_humanitarian_needs_overview_1.pdf"
#>
#> [[4]]
#> [1] "https://reliefweb.int/sites/reliefweb.int/files/resources/afg_2017_hno_english.pdf"
#>
#> [[5]]
#> [1] "https://reliefweb.int/sites/reliefweb.int/files/resources/afg_2016_hno_final_20151209.pdf"
#>
#> [[6]]
#> [1] "https://reliefweb.int/sites/reliefweb.int/files/resources/Afghanistan%20HRP%202015%20HNO%20Final%2023Nov2014%20%281%29.pdf"
#>
#> [[7]]
#> [1] "https://afg.humanitarianresponse.info/system/files/documents/files/Afg_2014HNO_FINALv2_0.pdf"
#> [2] "https://reliefweb.int/sites/reliefweb.int/files/resources/Afg_2014HNO_FINALv2_0.pdf"
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