如下面所示
install.packages("ggplot2")
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  unable to access index for repository http://cran.rstudio.com/src/contrib:
  cannot open URL 'http://cran.rstudio.com/src/contrib/PACKAGES'
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
    InternetOpenUrl failed: ''
Warning in install.packages :
  unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin/src/contrib:[/url]
  cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/src/contrib/PACKAGES'
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  unable to access index for repository http://cran.rstudio.com/src/contrib:
  cannot open URL 'http://cran.rstudio.com/src/contrib/PACKAGES'
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  InternetOpenUrl failed: ''
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 ‘ggplot2’ is not available (for R version 3.3.0)
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  unable to access index for repository http://cran.rstudio.com/bin/windows/contrib/3.3:
  cannot open URL 'http://cran.rstudio.com/bin/windows/contrib/3.3/PACKAGES'
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  InternetOpenUrl failed: ''
Warning in install.packages :
  unable to access index for repository [url]http://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.3:
  cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.3/PACKAGES'
Error in nchar(homeDir) : invalid multibyte string, element 1
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