这个情况该怎么办呢
install.packages("ggplot2")
Installing package into ‘/Users/oujiro/Library/R/3.6/library’
(as ‘lib’ is unspecified)
Warning: unable to access index for repository https://mirrors.tongji.edu.cn/CRAN/src/contrib:
cannot open URL 'https://mirrors.tongji.edu.cn/CRAN/src/contrib/PACKAGES'
Warning: unable to access index for repository https://mirrors.tongji.edu.cn/CRAN/bin/macosx/el-capitan/contrib/3.6:
cannot open URL 'https://mirrors.tongji.edu.cn/CRAN/bin/macosx/el-capitan/contrib/3.6/PACKAGES'
Warning message:
package ‘ggplot2’ is not available (for R version 3.6.1)