Apply coord_flip() to single layer - r

Question

I would like to have a boxplot showing the same distribution underneath my histogram.
The code below almost works, but coord_flip() is being applied to all layers, instead of just the geom_boxplot layer.
plot1<-ggplot(newdatahistogram, aes_string(x=newdatahistogram[RawLocation])) +
xlab(GGVar) + ylab("Proportion of Instances") +
geom_histogram(aes(y=..density..), binwidth=1, colour="black", fill="white",origin=-0.5) +
scale_x_continuous(limits=c(-3,6), breaks=seq(0,5,by=1), expand=c(.01,0)) +
geom_boxplot(aes_string(x=-1, y=newdatahistogram[RawLocation])) + coord_flip()
How can I apply coord_flip() to a single layer?
Thank you!

Answer 1

I got it to work with a bit of a hack;
plot1 <- ggplot(newdatahistogram, aes_string(x=newdatahistogram[RawLocation], fill=(newdatahistogram[,"PQ"]))) +
xlab(GGVar) + ylab("Proportion of Observation") +
geom_histogram(aes(y=..density..), binwidth=1, colour="black", origin=-0.5) +
scale_x_continuous(limits=c(-1,6), breaks=seq(0,5,by=1), expand=c(.01,0)) +
scale_y_continuous(limits=c(-.2,1), breaks=seq(0,1,by=.2))
theme(plot.margin = unit(c(0,0,0,0), "cm"))
plot_box <- ggplot(newdatahistogram) +
geom_boxplot(aes_string(x=1, y=newdatahistogram[RawLocation])) +
scale_y_continuous(breaks=(0:5), labels=NULL, limits=c(-1,6), expand=c(.0,-.03)) +
scale_x_continuous(breaks=NULL) + xlab(NULL) + ylab(NULL) +
coord_flip() + theme_bw() +
theme(plot.margin = unit(c(0,0,.0,0), "cm"),
line=element_blank(),text=element_blank(),
axis.line = element_blank(),title=element_blank(), panel.border=theme_blank())
PB = ggplotGrob(plot_box)
plot1 <- plot1 + annotation_custom(grob=PB, xmin=-1.01, xmax=5.95, ymin=-.3,ymax=0)
This saves the rotated boxplot as a grob object and inserts it into the plot under the histogram.
I needed to play with the expansion element a bit to get the scales to line up,
but it works!
Seriously though, I think ggplot should have a horizontal boxplot available without cord_flip()... I tried to edit the boxplot code, but it was way too difficult for me!
Tried to post image, but not enough reputation

Answer 2

You can't: coord_flip always acts on all layers. However, you do have two alternatives:
The solution here shows how to use grid.arrange() to add a marginal histogram. (The comments in the question also link to a nice base-R way to do the same thing)
You could indicate density using a rug plot on of the four sides of the plot with plot1 + geom_rug(sides='r')
ggplot(mpg, aes(x=class, y=cty)) +
geom_boxplot() + geom_rug(sides="r")