Control layout when displaying a series of ggplot plots stored in a list

Question

I would like to control the layout when plotting a series of ggplots that I have stored in a list (generated automatically elsewhere).

I can plot series of plots as below.

library(ggplot2)
library(grid)
library(gridExtra)
p1 <- ggplot(mtcars, (aes(x=mpg, fill=as.factor(1)))) + geom_density() +  
                      scale_fill_manual(values="red") 
p2 <- ggplot(mtcars, (aes(x=mpg, fill=as.factor(1)))) + geom_density() +  
                      scale_fill_manual(values="orange") 
p3 <- ggplot(mtcars, (aes(x=mpg, fill=as.factor(1)))) + geom_density() +  
                      scale_fill_manual(values="yellow") 
p4 <- ggplot(mtcars, (aes(x=mpg, fill=as.factor(1)))) + geom_density() +  
                      scale_fill_manual(values="green") 
grid.arrange(p1, p2, p3, p4)

I can then change their layout, as indicated here.

grid.arrange(p1, p2, p3, p4, layout_matrix=cbind(c(1,2), c(3,4)))

I can also plot a series of plots if they are stored in a list, as indicated here.

myplotslist <- list(p1, p2, p3, p4)
do.call(grid.arrange, c(myplotslist, ncol=2))

But if I try to change the layout using layout_matrix, I get an error (and some warnings).

do.call(grid.arrange, c(myplotslist, ncol=2, layout_matrix=cbind(c(1,2), c(3,4))))

Error in gList(list(grobs = list(list(x = 0.5, y = 0.5, width = 1, height = 1,  : 
  only 'grobs' allowed in "gList"
In addition: Warning messages:
1: In grob$wrapvp <- vp : Coercing LHS to a list
2: In grob$wrapvp <- vp : Coercing LHS to a list
3: In grob$wrapvp <- vp : Coercing LHS to a list
4: In grob$wrapvp <- vp : Coercing LHS to a list

I have tried coercing the plot objects to grobs, but encounter the same error.

myplotslist2 <- list(ggplotGrob(p1), ggplotGrob(p2), ggplotGrob(p3), ggplotGrob(p4))

I am using R 3.2.1, ggplot2 2.0.0, grid 3.2.1, and gridExtra 2.0.0, and would be extremely grateful for suggestions.

Answer 1

The arguments to the function you pass to do.call are really supposed to be a list. From ?do.call:

args a list of arguments to the function call. The names attribute of args gives the argument names.

The errors are telling you that your other arguments are getting passed to the grobs argument of grid.arrange. To stop that, put it in a list (c flattens too much here) and specify the grobs argument name for myplotslist:

do.call(grid.arrange, list(grobs = myplotslist, ncol=2, layout_matrix=cbind(c(1,2), c(3,4))))

...or you can ditch do.call entirely (h/t Baptiste):

grid.arrange(grobs = myplotslist, ncol=2, layout_matrix=cbind(c(1,2), c(3,4)))