R：修改下载安装包install.package的默认存储位置

参考文献：
R语言修改下载安装包install.package的默认存储位置

下载 ISLR、pls 这2个包。
install.packages(c(“ISLR”, “pls”))
发现：
（1）压缩包位于C:\Users\Administrator\AppData\Local\Temp\RtmpgnBETz\downloaded_packages
（2）解压后的包位于
E:\R\R-3.6.2\library（也就是R软件自带包的地址）

目的：更改压缩包地址变为E:\R\RStudiowork\downloaded_packages

方法：
（1）先卸载已安装的包 ISLR、pls：在 RStudio 界面里的 Packages 里卸载。原有的压缩包与解压包都将被删除。
（2）重启 RStudio
（3）修改 destdir 参数
install.packages(c(“ISLR”, “pls”), destdir = “E:/R/RStudiowork/downloaded_packages”)

未修改路径的下载包方法：

> install.packages(c("ISLR", "pls"))
WARNING: Rtools is required to build R packages but is not currently installed. Please download and install the appropriate version of Rtools before proceeding:

https://cran.rstudio.com/bin/windows/Rtools/
试开URL’https://cran.rstudio.com/bin/windows/contrib/3.6/ISLR_1.2.zip'
Content type 'application/zip' length 2924273 bytes (2.8 MB)
downloaded 2.8 MB

试开URL’https://cran.rstudio.com/bin/windows/contrib/3.6/pls_2.7-2.zip'
Content type 'application/zip' length 1230264 bytes (1.2 MB)
downloaded 1.2 MB

package ‘ISLR’ successfully unpacked and MD5 sums checked
package ‘pls’ successfully unpacked and MD5 sums checked

The downloaded binary packages are in
	C:\Users\Administrator\AppData\Local\Temp\RtmpgnBETz\downloaded_packages

修改路径的下载包方法：

> install.packages(c("ISLR", "pls"), destdir = "E:/R/RStudiowork/downloaded_packages")
WARNING: Rtools is required to build R packages but is not currently installed. Please download and install the appropriate version of Rtools before proceeding:

https://cran.rstudio.com/bin/windows/Rtools/
试开URL’https://cran.rstudio.com/bin/windows/contrib/3.6/ISLR_1.2.zip'
Content type 'application/zip' length 2924273 bytes (2.8 MB)
downloaded 2.8 MB

试开URL’https://cran.rstudio.com/bin/windows/contrib/3.6/pls_2.7-2.zip'
Content type 'application/zip' length 1230264 bytes (1.2 MB)
downloaded 1.2 MB

package ‘ISLR’ successfully unpacked and MD5 sums checked
package ‘pls’ successfully unpacked and MD5 sums checked