Reduce margins around ggplot2 pie chart

Question

I am including a pie chart in a document and the other charts are in ggplot2 , so I'd like to use ggplot2 to keep the charts consistent. However, the pie chart does not extend to the margins

dat <- structure(list(y = c(0.0714285714285714, 
                            0.0714285714285714, 
                            0.107142857142857, 
                            0.160714285714286, 
                            0.25, 
                            0.339285714285714), 
                      x = structure(c(1L, 3L, 4L, 5L, 6L, 2L), 
                                    .Label = c("1 to 5", "6", "7", "8", "9", "10"), 
                                    class = "factor")), 
                 class = "data.frame", 
                 .Names = c("y", "x"), row.names = c(NA, -6L))

ggplot(dat, aes(x = factor(1), y = y, fill = factor(x))) + 
  geom_bar(width = 1, stat = "identity") + 
  coord_polar(theta  = "y") + 
  theme_grey()

I'd be using theme_void() ; I've used theme_grey to illustrate the point: the edges of the pie chart don't extend far enough in the panel. How can I make the diameter of the pie equal (or very close to) the width of the panel? Modifying width=1 or scale_x_discrete(expand = c(0,0)) has no effect. The arguments to coord_polar don't seem to provide any clue either.

Answer 1

This doesn't actually solve your the problem but it does enlarge the area of the pie chart to approximately the initial size of the panel.

ggplot(dat, aes(x = factor(1), y = y, fill = factor(x))) + 
geom_bar(width = 1, stat = "identity") + 
coord_polar(theta  = "y") + 
guides(fill=guide_legend(override.aes=list(colour=NA))) +
theme(panel.grid.major = element_blank(),
      panel.grid.minor = element_blank(),
      axis.text.x=element_blank(),
      plot.margin = unit(c(-.75,-.75,-.75,-.75),"cm")
      )