I'm working with the really awesome library ggplot2. I figured out how to set the aspect ratio of a plot by using coord_fixed
. Now, I'd like to save the plot to a PDF with a specified width (e.g 10 cm) and let required height get calculated. I did not figure out how to achieve this. Is this even possible?
You can use grid functions to calculate the full size of the ggplot grob, but there are (edit: at least) two caveats:
an extra device window will open, to do the unit conversion
the plot panel size will be 0 by default, as it is meant to be calculated on-the-fly according to the device (viewport) it lives in, not the opposite.
That being said, the following function attempts to open a device that fits the ggplot exactly,
library(ggplot2)
library(grid)
sizeit <- function(p, panel.size = 2, default.ar=1){
gb <- ggplot_build(p)
# first check if theme sets an aspect ratio
ar <- gb$plot$coordinates$ratio
# second possibility: aspect ratio is set by the coordinates, which results in
# the use of 'null' units for the gtable layout. let's find out
g <- ggplot_gtable(gb)
nullw <- sapply(g$widths, attr, "unit")
nullh <- sapply(g$heights, attr, "unit")
# ugly hack to extract the aspect ratio from these weird units
if(any(nullw == "null"))
ar <- unlist(g$widths[nullw == "null"]) / unlist(g$heights[nullh == "null"])
if(is.null(ar)) # if the aspect ratio wasn't specified by the plot
ar <- default.ar
# ensure that panel.size is always the larger dimension
if(ar <= 1 ) panel.size <- panel.size / ar
g$fullwidth <- convertWidth(sum(g$widths), "in", valueOnly=TRUE) +
panel.size
g$fullheight <- convertHeight(sum(g$heights), "in", valueOnly=TRUE) +
panel.size / ar
class(g) <- c("sizedgrob", class(g))
g
}
print.sizedgrob <- function(x){
# note: dev.new doesn't seem to respect those parameters
# when called from Rstudio; in this case it
# may be replaced by x11 or quartz or ...
dev.new(width=x$fullwidth, height=x$fullheight)
grid.draw(x)
}
p1 <- ggplot(mtcars, aes(x = wt, y = mpg)) + geom_point() + coord_fixed() +
theme(plot.background = element_rect(colour = "red"))
p2 <- p1 + aes(x = mpg, y = wt)
# need for an explicit dummy device open, otherwise it's a bit off
# for no apparent reason that I can understand
dev.new()
sizeit(p1, 0.1)
sizeit(p2, 2)