Using arrangeGrob to add a sub plot as a legend - r

Question

I'm trying to graph two plots together, where one I a main plot and the other is a sub plot that I'd like to be located in the legend area of the main plot.
This code produces this plot:
gLegend <- function(a.gplot){
tmp <- ggplot_gtable(ggplot_build(a.gplot))
leg <- which(sapply(tmp$grobs, function(x) x$name) == "guide-box")
legend <- tmp$grobs[[leg]]
return(legend)
}
set.seed(1)
main.df <- data.frame(group=rep(LETTERS[1:4],3),
y=rnorm(12),x=c(rep(1,4),rep(2,4),rep(3,4)),col=rep(c("gray","blue","red","magenta"),3))
main.df$group <- factor(main.df$group,levels=LETTERS[1:4])
sub.df <- data.frame(group=c("B","C","D"),x=1:3,effect=runif(3,0,1),col=c("blue","red","magenta"))
sub.df$group <- factor(sub.df$group,levels=LETTERS[2:4])
main.plot <- ggplot(main.df,aes(x=x,y=y,color=factor(group)))+geom_point(size=3)+facet_wrap(~group,ncol=4)+scale_fill_manual(values=c("gray","blue","red","magenta"),labels=c("A","B","C","D"),name="group")+scale_colour_manual(values=c("gray","blue","red","magenta"),labels=c("A","B","C","D"),name="group")+scale_x_continuous(breaks=unique(main.df$x))
sub.plot <- ggplot(sub.df,aes(x=x,y=effect,color=factor(group)))+geom_point(size=2)+scale_fill_manual(values=c("blue","red","magenta"),labels=c("B","C","D"),name="group",guide=FALSE)+scale_colour_manual(values=c("blue","red","magenta"),labels=c("B","C","D"),name="group",guide=FALSE)+labs(x="group",y="effect")+ggtitle("effect summary")+scale_x_continuous(breaks=unique(sub.df$x),labels=c("B","C","D"))
sub.plot.grob <- ggplotGrob(sub.plot)
combined.plot <- arrangeGrob(main.plot+theme(legend.position="none"),widths=c(0.75,0.25),arrangeGrob(20,sub.plot.grob),ncol=2)
What I'd like to do is get rid of the legend of the main plot.
If I add guide=FALSE to scale_fill_manual scale_colour_manual gLegend throws the error:
Error in tmp$grobs[[leg]] :
attempt to select less than one element in get1index
Obviously because it cannot fine "guide-box"
Any idea how to solve this?

Answer 1

Here is an alternative solution using cowplot
library(ggplot2)
library(cowplot)
theme_set(theme_bw()) #cowplot automatically sets theme_classic
set.seed(1)
main.df <- data.frame(group=rep(LETTERS[1:4],3),
y=rnorm(12),x=c(rep(1,4),rep(2,4),rep(3,4)),col=rep(c("gray","blue","red","magenta"),3))
main.df$group <- factor(main.df$group,levels=LETTERS[1:4])
sub.df <- data.frame(group=c("B","C","D"),x=1:3,effect=runif(3,0,1),col=c("blue","red","magenta"))
sub.df$group <- factor(sub.df$group,levels=LETTERS[2:4])
sub.plot <- ggplot(sub.df,aes(x=x,y=effect,color=factor(group)))+
geom_point(size=2)+
scale_fill_manual(values=c("blue","red","magenta"),labels=c("B","C","D"),name="group",guide=FALSE)+
scale_colour_manual(values=c("blue","red","magenta"),labels=c("B","C","D"),name="group",guide=FALSE)+
labs(x="group",y="effect")+
ggtitle("effect summary")+
scale_x_continuous(breaks=unique(sub.df$x),labels=c("B","C","D"))
main.plot <- ggplot(main.df,aes(x=x,y=y,color=factor(group)))+
geom_point(size=3)+facet_wrap(~group,ncol=4)+
scale_fill_manual(values=c("gray","blue","red","magenta"),labels=c("A","B","C","D"),name="group")+
scale_colour_manual(values=c("gray","blue","red","magenta"),labels=c("A","B","C","D"),name="group")+
scale_x_continuous(breaks=unique(main.df$x)) +
theme(legend.position = "none")
ggdraw() +
draw_plot(main.plot, x = 0, y = 0, width = 0.75, height = 1) +
draw_plot(sub.plot, 0.75, 0, .25, .5)

Answer 2

try this,
grid.arrange(ggplot(), ggplot(),
layout_matrix=matrix(c(1,1,NA,2), 2), widths=c(1.5,1))

Answer 3

Here is solution using grid package, if you want a blank space where is the current legend:
library(grid)
set.seed(1)
main.df <- data.frame(group=rep(LETTERS[1:4],3),
y = rnorm(12),
x = c(rep(1,4), rep(2,4), rep(3,4)),
col = rep(c("gray", "blue", "red", "magenta"), 3))
main.df$group <- factor(main.df$group,levels=LETTERS[1:4])
sub.df <- data.frame(group=c("B", "C", "D"),
x = 1:3,
effect = runif(3, 0, 1),
col = c("blue", "red", "magenta"))
sub.df$group <- factor(sub.df$group, levels=LETTERS[2:4])
main.plot <- ggplot(main.df, aes(x = x,y = y, color = factor(group))) +
geom_point(size = 3) + facet_wrap(~group, ncol = 4) +
scale_fill_manual(values = c("gray", "blue", "red", "magenta"),
labels = c("A", "B", "C", "D"),name = "group") +
scale_colour_manual(values = c("gray", "blue", "red", "magenta"),
labels = c("A", "B", "C", "D"), name = "group") +
scale_x_continuous(breaks = unique(main.df$x)) + guides(color = F)
sub.plot <- ggplot(sub.df, aes(x = x, y = effect, color = factor(group))) +
geom_point(size = 2) +
scale_fill_manual(values = c("blue", "red", "magenta"),
labels = c("B", "C", "D"), name= "group" ,guide = FALSE) +
scale_colour_manual(values = c("blue", "red", "magenta"),
labels = c("B", "C", "D"), name = "group", guide=FALSE) +
labs(x = "group", y = "effect") +
ggtitle("effect summary") +
scale_x_continuous(breaks = unique(sub.df$x), labels = c("B", "C", "D"))
blank = grid.rect(gp = gpar(col = "white"))
sub.plot.grob <- arrangeGrob(blank, sub.plot, ncol = 1)
combined.plot <- arrangeGrob(main.plot, sub.plot.grob, ncol=2, widths=c(0.75,0.25))
grid.arrange(combined.plot)