直接
install.packages("forecast")
就可以了

注意安装包和你用不用Rstudio没有关系。Rstudio只是一个R的GUI，也就是一个很好用的外壳，里面的东西都是R的

非常感谢，这个函数太有帮助了，以后就这么用了，谢谢大神

输入install.packages("forecast")后，
显示
package ‘fracdiff’ successfully unpacked and MD5 sums checked
Error in read.dcf(file.path(pkgname, "DESCRIPTION"), c("Package", "Type")) :
  cannot open the connection
In addition: Warning messages:
1: In download.file(url, destfile, method, mode = "wb", ...) :
  downloaded length 43533 != reported length 3004766
2: In unzip(zipname, exdir = dest) : error 1 in extracting from zip file
3: In read.dcf(file.path(pkgname, "DESCRIPTION"), c("Package", "Type")) :
  cannot open compressed file 'Rcpp/DESCRIPTION', probable reason 'No such file or directory'
>
这是什么状况啊……

哥 说你没法链接啊 你关了重开试试