解决R/RStudio中安装包“无法与服务器建立连接”

　　这几天在用RStudio写程序的时候突然出现无法从网络直接安装r包的问题，也无法从本地直接安装。通过多方尝试找到了问题解决的办法，现在记录在这里。程序报错如下：
　　

> install.packages('REmap')
Warning in install.packages :
  unable to access index for repository https://cran.rstudio.com/src/contrib:
  cannot open URL 'https://cran.rstudio.com/src/contrib/PACKAGES'
Warning in install.packages :
  unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin/src/contrib:
  cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/src/contrib/PACKAGES'
Warning in install.packages :
  unable to access index for repository https://cran.rstudio.com/src/contrib:
  cannot open URL 'https://cran.rstudio.com/src/contrib/PACKAGES'
Warning in install.packages :
  unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin/src/contrib:
  cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/src/contrib/PACKAGES'
Warning in install.packages :
  package ‘REmap’ is not available (for R version 3.4.1)
Warning in install.packages :
  unable to access index for repository https://cran.rstudio.com/bin/windows/contrib/3.4:
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.4/PACKAGES'
Warning in install.packages :
  unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.4:
  cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.4/PACKAGES'
Warning: unable to access index for repository https://cran.rstudio.com/src/contrib:
  cannot open URL 'https://cran.rstudio.com/src/contrib/PACKAGES'
Warning: unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin/src/contrib:
  cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/src/contrib/PACKAGES'

　　网络上主流的解决方式是在tools-global options-packages中切换下载的镜像，有很多人反映他们的问题通过这个方法得到了解决，但是我换过很多镜像都没有用。
　　另一种方式是修改文件，在安装文件夹中找到Rprofile.site文件，我的路径是D:\Program Files\R\R-3.4.1\etc，用记事本打开，在里面添加语句：
　　

# set a CRAN mirror
local({r <- getOption(“repos”)
r[“CRAN”] <- “http://mirrors.tuna.tsinghua.edu.cn/CRAN/”
options(repos=r)}

　　这也是设置镜像的方法，与方法一相同。对我也没用。

　　之后了解到R中install.packages()是从ie浏览器中连接镜像的，所以无法连接服务器很可能是在ie这一环节出现了问题。打开电脑的ie浏览器看能不能正常上网，如果显示代理问题，在工具-internet选项-连接中将局域网设置里的代理服务器这一项去掉勾选。这样就可以正常上网了。再检查RStudio也能够正常安装r包了。

　　之后出现另外一个问题：
　　

> install.packages('sp')
trying URL 'https://cran.wu.ac.at/bin/windows/contrib/3.4/sp_1.2-5.zip'
Content type 'application/zip' length 1538503 bytes (1.5 MB)
downloaded 1.5 MB

package ‘sp’ successfully unpacked and MD5 sums checked
Warning in install.packages :
  unable to move temporary installation ‘D:\Program Files\R\R-3.4.1\library\file4041367c44\sp’ to ‘D:\Program Files\R\R-3.4.1\library\sp’

The downloaded binary packages are in
    C:\Users\asus\AppData\Local\Temp\RtmpWOz6Xu\downloaded_packages

　　无法将安装包从临时目录中转移，原因是杀毒软件可能禁止了这样的操作。在杀毒软件的白名单中加入R安装在的文件夹，重新启动RStudio问题即可解决。或者比较麻烦一点的话就是在临时目录中解压这个压缩文件到R安装目录中的library文件夹中。