当我们用启动R安装一些R包的时候 提示: Warning: unable to access index for repository https://mirrors.eliteu.cn/CRAN/src/contrib: cannot open URL 'https://mirrors.eliteu.cn/CRAN/src/contrib/PACKAGES' Warning message: package 'RPMM' is not available (for R version 3.6.
A data frame is used for storing data tables. It is a list of vectors of equal length. For example, the following variable df is a data frame containing three vectors n, s, b. n = c(2, 3, 5) s = c("aa", "bb", "cc") b = c(TRUE