低级绘图--网格线

grid(nx = NULL, ny = nx, col = "lightgray", lty = "dotted",
     lwd = par("lwd"), equilogs = TRUE)

nx：垂直网格的数据
ny：水平网格的数据

barplot(VADeaths,besides=TRUE,col = cm.colors(5))
grid()
barplot(VADeaths,besides=TRUE,col = cm.colors(5))
grid(NA,7,lty = 2,lwd = 1.5,col = "green")