How to set different "size" in one ggplot() object

[Ming Little]

Hi,

I want to draw a plot with both geom_point() and geon_segment(), and I need to adjust the size of the points or the lines in the plot. It is easy to do this with scale_size(range= c(0,any value)).

An example plot code:

ggplot(data = data.frame(a=1:3,b=2:4,s=3:5,c=as.character(4:6)))+
  geom_segment(mapping = aes(x=a,xend=b,y=b,yend=a,size=s))+
  geom_point(mapping = aes(x=a,y=b,size=s,color=c))+

  scale_size(range(0,5))

But if i want to set different range to points and lines, i found i can't do that because a ggplot() can have only one scale. I cant set a range of c(0,5) to points and set a different range of c(0,2) to the lines. 

I usually the same problem encounter the same problem when i want to set more than one scale of color to different layers in one plot.

I have solved the problem by modifing the GeomPoint and geom_point(), set a new aes name like point_size to make it separate from the normal size aes. 

 But i don't think all the ggplot2 users can do this and maybe there is any "normal way" or "offical way" to set different size in one ggplot() without modifing the original code?

[wouter...@hotmail.com]

There's no "normal way" using just ggplot2. But there are extension packages, like ggnewscale (https://github.com/eliocamp/ggnewscale) or relayer (https://github.com/clauswilke/relayer). These make it a lot easier than having to modify the geoms.

Something like:

library(ggnewscale)

ggplot(data = data.frame(a=1:3,b=2:4,s=3:5,c=as.character(4:6)))+
  geom_segment(mapping = aes(x=a,xend=b,y=b,yend=a,size=s))+

  scale_size(range = c(0, 2)) +

  new_scale('size') +

  geom_point(mapping = aes(x=a,y=b,size=s,color=c))+

  scale_size(range = c(0,5))

Do note that in your example, this isn't necessary, since the size of lines should now be mapped to linewidth, not size:

ggplot(data = data.frame(a=1:3,b=2:4,s=3:5,c=as.character(4:6)))+

    geom_segment(mapping = aes(x=a,xend=b,y=b,yend=a,linewidth=s))+
    geom_point(mapping = aes(x=a,y=b,size=s,color=c))+
    scale_linewidth(range = c(0, 2)) +
    scale_size(range = c(0, 5))