使用“download.file"下载多个文件功能

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 向量 (pdfurls) 和一个目标文件名向量 (destinations):

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")

我使用的代码是:

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

然而，当我运行代码时，R 访问 URL，下载第一个 PDF，并一遍又一遍地重复下载同一个 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:R 函数的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?

代码类似于这里的帖子:如何在 R 中使用循环下载多个文件? 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

我认为你的循环基本没问题，只是你忘记索引 urls 和 destinations 对象.

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

实际上，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")
}

或者按照 @docendodiscimus 的建议使用 Map :

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

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