Convert plot to grob and ggplot object (original) (raw)

grid
ggplot2
Align plots

grid

library("grid")
library("ggplotify")

p1 <- as.grob(~barplot(1:10))
p2 <- as.grob(expression(plot(rnorm(10))))
p3 <- as.grob(function() plot(sin))

library("vcd")
data(Titanic)
p4 <- as.grob(~mosaic(Titanic))

library("lattice")
data(mtcars)
p5 <- as.grob(densityplot(~mpg|cyl, data=mtcars))

as.grob function accepts plot function call asexpression or formula, or a function that plots to an R graphics device. The plots can be generated by base graphics (p1, p2, p3) orgrid (p4). If the plot function produce graphic object, it can be directly used as input (p5, can be trellis object by lattice package,meme object by meme package,upset object by ‘UpSetR’ package, etc.).

It will convert the plot to grob object, so that it can be compatible with grid system and related packages.

We can now use grid.draw to plot p1 andp2, and use pushViewport to embed plot inside another plot.

grid.newpage()
grid.draw(p1)
vp = viewport(x=.35, y=.75, width=.35, height=.3)
pushViewport(vp)
grid.draw(p2)
upViewport()

If you are not family with grid, you can useggplot2 to do similar task (e.g. p8in the below example).

ggplot2

All the plots that can be converted to grob are supported to be converted to ggplot object by usingas.ggplot function.

library(ggplot2)
p1 <- as.ggplot(~barplot(1:10)) +
    annotate("text", x = .6, y = .5,
             label = "Hello Base Plot", size = 5,
             color = 'firebrick', angle=45)

p2 <- as.ggplot(expression(plot(rnorm(10))))
p3 <- as.ggplot(function() plot(sin))

p4 <- as.ggplot(~mosaic(Titanic))

p5 <- as.ggplot(densityplot(~mpg|cyl, data=mtcars))

Align plots

With all the plots converted to ggplot objects, we are able to align plots produced by ‘base’ and ‘grid’ graphic systems usingcowplot or patchwork.

library(cowplot)

library(colorspace)
col <- rainbow_hcl(3)
names(col) <- unique(iris$Species)

color <- col[iris$Species]
p6 <- as.ggplot(~plot(iris$Sepal.Length, iris$Sepal.Width, col=color, pch=15))

p7 <- ggplot(iris, aes(Sepal.Length, Sepal.Width, color=Species)) +
    geom_point(shape=15) + scale_color_manual(values=col, name="")

legend <- get_legend(p7)

## also able to annotate base or other plots using ggplot2
library(ggimage)
p8 <- p6 + geom_subview(x=.7, y=.78, subview=legend)


p9 <- as.ggplot(~image(volcano))

plot_grid(p1, p2, p3, p4, p5, p6, p7, p8, p9, ncol=3, labels=LETTERS[1:9])