Custom legend in ggpairs disappears after changing theme - r

Question

I am having problems with a vanishing legend in ggpairs.
I add a legend inside the top part of a lower triangular ggpairs plot as follows.
First I create a ggpairs plot without legend then I strip the legend I want from and ad hoc graph and place in the ggpairs plot it with putPlot. It works nicely until I try to modify the theme which makes the legend disappear.
# 1 produce graph without legend
library(GGally)
library(ggplot2)
plotwithoutlegend <-ggpairs(
iris,
columns=1:4,
switch="both",
upper="blank",
mapping=aes(color = Species,
shape= Species,
fill=Species,
alpha=0.5)
)
#2 grab the legend from a graph with the legend I want (without alpha).
auxplot <- ggplot(iris, aes(x=Petal.Length, y=Petal.Width,
color=Species,
shape=Species,
fill=Species)) + geom_point()
mylegend <- grab_legend(auxplot)
# 3 place the legend in the ggpairs grid with putPlot
graph1 <- putPlot(plotwithoutlegend,mylegend,3,4)
show(graph1)
This produces a graph with the legend in the desired place.
ggpairs graph with legend before changing theme:
However if I change some aspect of the theme the legend disappears.
graph2 <- graph1 +theme(strip.background =element_blank(), strip.placement = "outside")
show(graph2)
Legend vanishes after changing theme:

Answer 1

I had similar issue. I think you need to use library(grid). see my solution.
# plotwithoutlegend
plotwithoutlegend <- ggpairs(
iris,
columns=1:4,
switch="both",
upper="blank",
mapping=aes(color = Species,
shape= Species,
fill=Species,
alpha=0.5)
)+
theme(strip.background =element_blank(), strip.placement = "outside")
#2 grab the legend from a graph with the legend I want (without alpha).
auxplot <- ggplot(iris, aes(x=Petal.Length, y=Petal.Width,
color=Species,
shape=Species,
fill=Species)) + geom_point()
mylegend <- grab_legend(auxplot)
##### plot legend with plot
grid.newpage()
grid.draw(plotwithoutlegend)
vp = viewport(x=.9, y=.75, width=.35, height=.3) ## control legend position
pushViewport(vp)
grid.draw(mylegend)
upViewport()

Answer 2

Learned here: Legend using ggpairs
# first run your code until
graph2 <- graph1 +theme(strip.background =element_blank(), strip.placement = "outside")
# then run this code
colidx <- c(3,5,6,7)
for (i in 1:length(colidx)) {
# Address only the diagonal elements
# Get plot out of plot-matrix
inner <- getPlot(graph2, i, i);
# Add ggplot2 settings (here we remove gridlines)
inner <- inner + theme(panel.grid = element_blank()) +
theme(axis.text.x = element_blank())
# Put it back into the plot-matrix
graph2 <- putPlot(graph2, inner, i, i)
for (j in 1:length(colidx)){
if((i==1 & j==1)){
# Move the upper-left legend to the far right of the plot
inner <- getPlot(graph2, i, j)
inner <- inner + theme(legend.position=c(length(colidx)-0.25,0.50))
graph2 <- putPlot(graph2, inner, i, j)
}
else{
# Delete the other legends
inner <- getPlot(graph2, i, j)
inner <- inner + theme(legend.position="none")
graph2 <- putPlot(graph2, inner, i, j)
}
}
}
# then run this code
show(graph2)