使用"download.file"下载多个文件.功能 [英] Download multiple files using "download.file" function

问题描述

我正在尝试使用R从网站下载PDF.

I am trying to download PDFs from a website using R.

我有一个PDF-URL的向量( pdfurls )和一个目标文件名的向量(目的地):

I have a vector of the PDF-URLs (pdfurls) and a vector of destination file names (destinations):

例如:

pdfurls <- c("http://website/name1.pdf", "http://website/name2.pdf")
destinations <- c("C:/username/name1.pdf", "C:/username/name2.pdf")

我正在使用的代码是:

for(i in 1:length(urls)){
    download.file(urls, destinations, mode="wb")}

但是，当我运行代码时，R访问URL，下载第一个PDF，然后一次又一次地重复下载相同的PDF.

However, when I run the code, R accesses the URL, downloads the first PDF, and repeats downloading the same PDF over and over again.

我已经阅读了这篇文章: for R循环，并且想知道是否这与函数本身有关，还是我的循环有问题?

I have read this post: for loop on R function and was wondering if this has something to do with the function itself or is there a problem with my loop?

代码类似于此处的帖子:如何使用R中的循环下载多个文件?，所以我想知道为什么它不起作用以及是否有更好的方法使用R下载多个文件.

The code is similar to the post here: How to download multiple files using loop in R? so I was wondering why it is not working and if there is a better way to download multiple files using R.

推荐答案

除了您忘记索引urls和destinations对象，我认为您的循环基本上很好.

I think your loop is mostly fine, except you forgot to index the urls and destinations objects.

切切地，我建议在定义for循环时养成使用seq_along而不是1:length()的习惯.

Tangentially, I would recommend getting in the habit of using seq_along instead of 1:length() when defining for loops.

for(i in seq_along(urls)){
    download.file(urls[i], destinations[i], mode="wb")
}

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或按照 @docendodiscimus 的建议使用地图:

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Or using Map as suggested by @docendodiscimus :

Map(function(u, d) download.file(u, d, mode="wb"), urls, destinations)

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