library(ggplot2)
library(ggpubr)

var_list <- rep(names(iris[1:4]),2)
plot_list <-  list()
for (i in 1:8) {
    p = ggplot(iris) +
        geom_boxplot(aes_string(x=var_list[i]))
    plot_list[[i]] = p
}
ggarrange(
    plotlist = plot_list,
    ncol=4,
    nrow=2
)