R: shared legend from a subplot to the 2x2 grid.ar

Question

This question already has an answer here:

• Global legend using grid.arrange (gridExtra) and lattice based plots 3 answers

I am working on this question here to get a legend from a subplot of 2x2 plots to its whole window. The goal is to get a single legend and then remove the other legends, only one legend is enough and that should be positioned on the right of the whole pane.

Perhaps relevant

1. Global legend using grid.arrange (gridExtra) and lattice based plots

Code

require(lattice)
require(gridExtra)

f<-function(x) as.double(as.character(x))   #factors converted to vectors https://stackoverflow.com/a/40680020/54964

data.female <- structure(list(N11.1 = structure(c(3L, 3L), .Label = c("", "0.0", 
"1.0", "N11"), class = "factor"), N22.1 = structure(c(2L, 2L), .Label = c("", 
"0.0", "2.0", "N22"), class = "factor"), N33.1 = structure(c(2L, 
2L), .Label = c("", "0.0", "N33"), class = "factor"), N44.1 = structure(2:3, .Label = c("", 
"0.0", "0.1", "0.2", "N44"), class = "factor"), N21.1 = structure(c(2L, 
2L), .Label = c("", "0.0", "N21"), class = "factor"), N31.1 = structure(c(2L, 
2L), .Label = c("", "0.0", "N31"), class = "factor"), N32.1 = structure(c(5L, 
7L), .Label = c("", "0.0", "10.8", "11.0", "12.0", "17.0", "20.9", 
"22.8", "24.0", "3.0", "4.0", "44.0", "N32"), class = "factor")), .Names = c("N11.1", 
"N22.1", "N33.1", "N44.1", "N21.1", "N31.1", "N32.1"), row.names = c("Sinus", 
"Arr/AHB"), class = "data.frame")

data.male <- structure(list(N11.1 = structure(c(3L, 3L), .Label = c("", "0.0", 
"1.0", "N11"), class = "factor"), N22.1 = structure(c(2L, 2L), .Label = c("", 
"0.0", "2.0", "N22"), class = "factor"), N33.1 = structure(c(2L, 
2L), .Label = c("", "0.0", "N33"), class = "factor"), N44.1 = structure(c(2L, 
2L), .Label = c("", "0.0", "0.1", "0.2", "N44"), class = "factor"), 
    N21.1 = structure(c(2L, 2L), .Label = c("", "0.0", "N21"), class = "factor"), 
    N31.1 = structure(c(2L, 2L), .Label = c("", "0.0", "N31"), class = "factor"), 
    N32.1 = structure(c(11L, 9L), .Label = c("", "0.0", "10.8", 
    "11.0", "12.0", "17.0", "20.9", "22.8", "24.0", "3.0", "4.0", 
    "44.0", "N32"), class = "factor")), .Names = c("N11.1", "N22.1", 
"N33.1", "N44.1", "N21.1", "N31.1", "N32.1"), row.names = c("Sinus", 
"Arr/AHB"), class = "data.frame")

ID<-c("Sinus","Arr/AHB")

tl <- "female"
p1 <- barchart(f(N11.1)+f(N22.1)+f(N33.1)+f(N44.1)+f(N21.1)+f(N31.1)+f(N32.1) ~ ID,
         data=data.female,
         auto.key=list(space='right'), 
         ylim=c(0,50),
     beside=TRUE,
     ylab = "Number of cases", 
     xlab = "Population/Sample",
     main = tl
         )
tl <- "male"
p2 <- barchart(f(N11.1)+f(N22.1)+f(N33.1)+f(N44.1)+f(N21.1)+f(N31.1)+f(N32.1) ~ ID,
         data=data.male,
         auto.key=list(space='right'),
         ylim=c(0,50),
     beside=TRUE,
     ylab = "Number of cases", 
     xlab = "Population/Sample",
     main = tl 
         )

# Just repeat two barcharts more to get 2x2 example
tl <- "female"
p3 <- barchart(f(N11.1)+f(N22.1)+f(N33.1)+f(N44.1)+f(N21.1)+f(N31.1)+f(N32.1) ~ ID,
         data=data.female,
         auto.key=list(space='right'), 
         ylim=c(0,50),
     beside=TRUE,
     ylab = "Number of cases", 
     xlab = "Population/Sample",
     main = tl
         )
tl <- "male"
p4 <- barchart(f(N11.1)+f(N22.1)+f(N33.1)+f(N44.1)+f(N21.1)+f(N31.1)+f(N32.1) ~ ID,
         data=data.male,
         auto.key=list(space='right'),
         ylim=c(0,50),
     beside=TRUE,
     ylab = "Number of cases", 
     xlab = "Population/Sample",
     main = tl)



grid.arrange(p1,p2,p3,p4, ncol=2, nrow=2,left=("LEFT TITLE"),right=("RIGHT"),bottom=("BOTTOM"), top=("TOP"))

that compiles producing the above grid plots but the following does not work because of the legend

grid.arrange(p1,p2,p3,p4, ncol=2, nrow=2,
        legend=list(space='right',
        text=c("N11.1","N22.1","N33.1","N44.1","N21.1","N31.1","N32.1"),
                    columns=1))

where the easiest way would be to inherit the legend from some of the subplots and use something like auto.key but I could not get such commond working so trying to create the grop object with legend command.

What is wrong in the legend command and is there any convient way to inherit the legend of the subplots to the whole pane so auto.key could be used in the exterior of the pane?

Helper questions

1. How does the colours get inherited from the automatic glob creation command auto.key to the legend?

2. Instead of manually writing the legend labels (N11.1,N22.1,...), how can you conveniently get it from a subplot?

Answer 1

I posted an answer here. The idea is to avoid inserting the key within the plot and use draw.key() to print a defined key anywhere on the final grid.arranged plot.