r - ggplot and axis numbers and labels

Question

i tried to build the following sample plot (see here for an example of a CIELAB Color Wheel). It is nearly finished, but there are still some small issues (see demo): - the numbers on the axis (the numbers, not sure how it is called in english) should be directly on the x/y axis (x=0 and y=0). at the moment i am using hline and vline to "add" the axis. Is there a way to move the whole axis? - the axis labels are next to the axis, but should be at the end of the axis as in the sample image. I am not sure if there is a solution for that. Tried to find the solution in the books of wickham and chang, but failed. not sure if such a plot is possible with ggplot2.

Sorry for the links, as a new user i am not allowed to post images :(

thanks a lot simon!

library(ggplot2)
circleFun <- function(center = c(0,0),diameter = 1, npoints = 100){
  r = diameter / 2
  tt <- seq(0,2*pi,length.out = npoints)
  xx <- center[1] + r * cos(tt)
  yy <- center[2] + r * sin(tt)
  return(data.frame(x = xx, y = yy))
}

# sample data for yellow
colorvals <- data.frame(file = 'Yellow.csv', L = 88.94026, a = -9.8599137, b=88.77139)

# build the circles for the plot
r20 <- circleFun(center = c(0, 0), diameter = 40, npoints = 100)
r40 <- circleFun(center = c(0, 0), diameter = 80, npoints = 100)
r60 <- circleFun(center = c(0, 0), diameter = 120, npoints = 100)
r80 <- circleFun(center = c(0, 0), diameter = 160, npoints = 100)
r100 <- circleFun(center = c(0, 0), diameter = 200, npoints = 100)
r120 <- circleFun(center = c(0, 0), diameter = 240, npoints = 100)
dat <- rbind(r20, r40, r60, r80, r100, r120)

# plot the data
ggplot(data = dat, aes(x, y)) +
  geom_path() +
  geom_hline() +
  geom_vline() +
  theme(legend.position = c(1,0), legend.justification=c(1,0)) +
  xlab("a* (Grün/Rot)") +
  ylab("b* (Gelb/Blau)") +
  labs(colour="L*") +
  geom_point(data = colorvals, aes(x = a, y = b), size=3) +
  geom_text(data = colorvals, aes(x = a, y = b, label = gsub(".csv", "", file)), size = 3, vjust=0,hjust=1.2)

Answer 1

moving the whole axis inside the plot panel is not straight-forward (arguably for good reasons). You can do it like this,

g <- ggplotGrob(p)

library(gtable)
# move the axis up in the gtable
g$layout[g$layout$name == "axis-b", c("t", "b")] <- 
  g$layout[g$layout$name == "panel", c("t", "b")] 
# extract the axis gTree and modify its viewport 
a <- g$grobs[[which(g$layout$name == "axis-b")]] 
a$vp <- modifyList(a$vp, list(y=unit(0.5, "npc")))
g$grobs[[which(g$layout$name == "axis-b")]] <- a


g$layout[g$layout$name == "axis-l", c("l", "r")] <- 
  g$layout[g$layout$name == "panel", c("l", "r")] 
# extract the axis gTree and modify its viewport 
b <- g$grobs[[which(g$layout$name == "axis-l")]] 
b$vp <- modifyList(b$vp, list(x=unit(0.5, "npc")))
g$grobs[[which(g$layout$name == "axis-l")]] <- b

#grid.newpage()
#grid.draw(g)


## remove all cells but panel
panel <- g$layout[g$layout$name == "panel",] 

gtrim <- g[panel$b, panel$r]
## add new stuff
gtrim <- gtable_add_rows(gtrim, unit(1,"line"), pos=0)
gtrim <- gtable_add_rows(gtrim, unit(1,"line"), pos=-1)
gtrim <- gtable_add_cols(gtrim, unit(1,"line"), pos=0)
gtrim <- gtable_add_cols(gtrim, unit(1,"line"), pos=-1)

gtrim <- gtable_add_grob(gtrim, list(textGrob("top"),
                                     textGrob("left", rot=90),
                                     textGrob("right", rot=90),
                                     textGrob("bottom")), 
                         t=c(1,2,2,3),
                         l=c(2,1,3,2))

grid.newpage()
grid.draw(gtrim)