Arranging GGally plots with gridExtra?

Question

I would like to arrange ggpairs graphs using arrangeGrob :

 library(GGally) library(gridExtra) df <- structure(list(var1 = 1:5, var2 = 4:8, var3 = 6:10), .Names = c("var1", "var2", "var3"), row.names = c(NA, -5L), class = "data.frame") p1 <- ggpairs(df, 1:3) p2 <- ggpairs(df, 1:2) p <- arrangeGrob(p1, p2, ncol=2) 

leading to this error:

 Error in arrangeGrob(p1, p2, ncol = 2) : input must be grobs! 

Is there any way around this problem?

Answer 1

Unfortunately, I do not see how this is possible.

First, it will not work with gridExtra , since arrangeGrob works with TableGrob objects:

 > ggplotGrob(qplot(1:100)) stat_bin: binwidth defaulted to range/30. Use 'binwidth = x' to adjust this. TableGrob (6 x 5) "layout": 8 grobs z cells name grob 1 0 (1-6,1-5) background rect[plot.background.rect.3349] 2 3 (3-3,3-3) axis-l absoluteGrob[GRID.absoluteGrob.3341] 3 1 (4-4,3-3) spacer zeroGrob[NULL] 4 2 (3-3,4-4) panel gTree[GRID.gTree.3329] 5 4 (4-4,4-4) axis-b absoluteGrob[GRID.absoluteGrob.3335] 6 5 (5-5,4-4) xlab text[axis.title.x.text.3343] 7 6 (3-3,2-2) ylab text[axis.title.y.text.3345] 8 7 (2-2,4-4) title text[plot.title.text.3347] 

The internal representation of the ggpairs object contains only the methods that need to be called, and not the actual humps:

 > str(p1$plots) List of 9 $ : chr "ggally_diagAxis(ggally_data, ggplot2::aes(x = var1))" $ : chr "ggally_cor(ggally_data, ggplot2::aes(x = var2, y = var1))" $ : chr "ggally_cor(ggally_data, ggplot2::aes(x = var3, y = var1))" $ : chr "ggally_points(ggally_data, ggplot2::aes(x = var1, y = var2))" $ : chr "ggally_diagAxis(ggally_data, ggplot2::aes(x = var2))" $ : chr "ggally_cor(ggally_data, ggplot2::aes(x = var3, y = var2))" $ : chr "ggally_points(ggally_data, ggplot2::aes(x = var1, y = var3))" $ : chr "ggally_points(ggally_data, ggplot2::aes(x = var2, y = var3))" $ : chr "ggally_diagAxis(ggally_data, ggplot2::aes(x = var3))" 

All the work of building the actual gnomes is done by GGally:::print.ggpairs . Take a look at the source code and you will see grid.newpage() along with several popViewport and pushViewport s. This means that even a low-level grid approach (like the one described here ) is not applicable, since your grid constructs will be overwritten by GGally:::print.ggpairs .

Of course, there is always a way. Changing the source code is always an option, although I believe that this is a long and difficult path for your task. I would be happy to be mistaken if anyone could come up with a simple workaround.

Answer 2

 library(GGally) library(gridExtra) library(grid) # reproducing initial data df <- structure(list(var1 = 1:5, var2 = 4:8, var3 = 6:10), .Names = c("var1", "var2", "var3"), row.names = c(NA, -5L), class = "data.frame") p1 <- ggpairs(df, 1:3) p2 <- ggpairs(df, 1:2) # declaring new method for drawing ggmatrix objects using grid.draw grid.draw.ggmatrix <- function(x, recording = T) print(x, gridNewPage = F) # then making them look like grob objects attributes(p1)$class <- c(attributes(p1)$class, "grob") attributes(p2)$class <- c(attributes(p2)$class, "grob") p <- arrangeGrob(p1, p2, ncol=2) grid.newpage() grid.draw(p)