library(ggplot2)
a <- ggplot(mpg,aes(hwy,cty)) + geom_point()
b <- ggplot(mpg,aes(class)) + geom_bar(aes(fill=class))
b + coord_cartesian()
b + coord_flip()
a + coord_fixed(ratio=1) + geom_abline()
a + coord_equal() + geom_abline()
b + coord_equal() + coord_flip()? ? ? ? ? ? ? #后坐標(biāo)系覆蓋前坐標(biāo)系
#Coordinate system already present. Adding new coordinate system, which will replace the existing one.
b + coord_polar(theta='x')
