set.seed(4230)   #设置种子数，大家取随机数一样
sample.ids <- sample(levels(yo$id),24)   #随机取ID

ggplot(aes(x=time,y=price),data = subset(yo,id %in% sample.ids))+     
  facet_wrap(~ id)+
  geom_line()+
  geom_point(aes(size=all.purchases),pch=1)    #按照大小来画圆圈