dt <- data.frame(
type=c("A","B"),
freq = c(1200,1650),
earn = c(0.94,0.98))
bp <- barplot((dt[,2]),yaxt="n",col="lightblue")
box()
lines(bp, dt[,3]*500, col = 4)
X轴放type A&B
Y1轴是earn 用trend
Y2轴是freq 用直方图呈现
因 2种资料差异很大
但画出来的图不美观
另外 如何显示双Y轴的座标轴

参考 https://goo.gl/HoRwIP