scale "y" axis on a polar plot in ggplot

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I'm trying to restrict the "y" axes (i.e. the radius) of a polar plot in ggplot. My data should range from 0 to 90. It should be simple, but I cannot understand what goes wrong:

foo <- tibble(theta=c(0,10,20),r=c(10,30,90))

foo %>% ggplot()+
  geom_point(aes(x=theta,y=r))+
  coord_polar()+
  scale_y_continuous(limits=c(0,90),expand=c(0,0),breaks=90)+
  scale_x_continuous(limits=c(0,360),expand=c(0,0),breaks=c(0,90,180,270))+
  theme(panel.grid.minor = element_blank(),
        panel.grid.major.y = element_line(colour="red"))

enter image description here

As you can see, the plot expands to 100 instead of 90. In addition I have two circles corresponding to major grid elements, one at 90 as required and one at 100. I added the "theme" statement to demonstrate that it does correspond to a major line. On the other hand the X data is properly scaled as required and "stops" at 360.

How can I force my graph to scale from 0 to 90, and remove this circle at 100 ?

Thanks !

coordinate-systems ggplot2 r
1 Answers

I think this is a bit of a bug, or at least a missing feature (equivalent behaviour in Cartesian co-ordinates could be prevented by setting hard limits via ylim in coord_cartesian, which is not available in coord_polar). There is no outer axis line in coord_polar, and a grid line seems to be used in its place, without respecting axis.line theme elements.

The only workaround I can find is somewhat "hacky", in that you can pass vectorized colours to the grid lines:

foo %>% 
  ggplot() +
  geom_point(aes(x = theta, y = r)) +
  coord_polar(clip = "off") +
  scale_y_continuous(limits = c(0, 90), expand = c(0, 0),  breaks = 90) +
  scale_x_continuous(limits = c(0, 360), expand = c(0, 0), 
                     breaks = c(0, 90, 180, 270)) +
  theme(panel.grid.minor   = element_blank(),
        panel.grid.major.y = element_line(colour = c("red", NA)))

enter image description here

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