api=read.table("clipboard",header=T)
library(ggplot2)
api2=subset(api,City %in% c("Shenyang","Changchun","Harbin","Beijing","Tianjin","Shijiazhuang","Taiyuan","Hohhot"))
ggplot(api2, aes(x=Year, y=api, group=Season,shape=Season)) + geom_line() + geom_point(aes(x=Year, y=api, group=Season,shape=c(1,12,4,19))) + theme_bw()+
facet_wrap(~City, ncol=4,shrink=T) +
opts(axis.text.x=theme_text(angle=-90, hjust=0), legend.position="right") + ylab("Quarterly average of DAPI")+xlab("Years")