讀取資料、新增變項
dta <- read.table("birth_college.txt",header = T)
dta$Year <- 1981:2009
dta$College <- dta$Entrance-40
tail(dta)## Birth Entrance Year College
## 24 9.6 87 2004 47
## 25 9.1 89 2005 49
## 26 9.0 91 2006 51
## 27 8.9 96 2007 56
## 28 8.6 97 2008 57
## 29 8.3 97 2009 57繪圖
p <- ggplot() +
geom_point(data=dta,aes(Year,Birth),pch=1)+
scale_y_continuous(
name=expression("Birth rate(0.1%)"),limits=c(0,60),breaks = seq(0,60,10),
sec.axis = sec_axis(~.+40,breaks = seq(40,100,10),name="Acceptance rate(%)"))+
geom_point(data=dta,aes(Year,College))+
theme(legend.position = 'topleft')+
theme(legend.background = element_rect(fill = 'white', colour = 'black'))
p + theme_bw()## Warning: Removed 13 rows containing missing values (geom_point).