1.The shape palette can deal with a maximum of 6 discrete values because more than 6 becomes difficult to discriminate;.....
解决方法：http://www.sthda.com/english/wiki/ggplot2-point-shapes
总结：ggplot2默认支持六种不同点形，若要增加，如需要七种不同的的点型：
ggplot(data,aes(x=time,y=value))+
geom_point(aes(shape=school),size=0.8)+
geom_line()+
scale_shape_manual(values=c(1,2,4,5,7,8,13))
数字——点型对应如下：