Overall Label for Facets

Question

Here is some minimal code to generate a graph with two sets of facets.

library("ggplot2", quietly = TRUE, warn.conflicts = FALSE)
library("RColorBrewer", quietly = TRUE, warn.conflicts = FALSE)
val.a <- rnorm(10)
val.b <- rnorm(10)
val.c <- c("A","B","A","A","B","B","B","B","A","B")
val.d <- c("D","D","E","D","E","E","E","D","D","E")
val.e <- rnorm(10)
maya <- data.frame(val.a,val.b,val.c,val.d,val.e)
ggplot(maya, aes(x=val.a, y=val.b)) +
  geom_point(shape=20,size=3, aes(colour=val.e)) +
  facet_grid(val.c~val.d) +
  xlab("Leonardo") + ylab("Michaelangelo") +
  scale_colour_gradientn(colours=brewer.pal(9,"YlGnBu"), name="Splinter")

I can't figure out how to add an overall facet label so that the names Donatello and Raphael are on the top and right hand side axis.

I saw some similar solutions on SO, but I can't make heads or tails of the code. Please would you suggest an answer to my conundrum?

Similar question here, but it fails for me if I have more than two facets. The labels show up somewhere inside the graph. Is there a way to make this work for the general case?

So I tried rawr's solution at the link above, and it ended up at the same place for multiple columns. Here's the code updated to rawr's solution, but it's producing the labels in unexpected (for me because I don't understand the solution) places.

library("ggplot2", quietly = TRUE, warn.conflicts = FALSE)
library("RColorBrewer", quietly = TRUE, warn.conflicts = FALSE)
val.a <- rnorm(20)
val.b <- rnorm(20)
val.c <- c("A","B","C","D","E","F","G","H","I","J")
val.d <- c("A","B","C","D","E","F","G","H","I","J")
val.e <- rnorm(20)
maya <- data.frame(val.a,val.b,val.c,val.d,val.e)
p <- ggplot(maya, aes(x=val.a, y=val.b)) + geom_point(shape=20,size=3, aes(colour=val.e)) + facet_grid(val.c~val.d) + xlab("Leonardo") + ylab("Michaelangelo") + scale_colour_gradientn(colours=brewer.pal(9,"YlGnBu"), name="Splinter")
z <- ggplotGrob(p)

library(grid)
library(gtable)
# add label for right strip
z <- gtable_add_cols(z, unit(z$width[[7]], 'cm'), 7)
z <- gtable_add_grob(z, 
                     list(rectGrob(gp = gpar(col = NA, fill = gray(0.5))),
                          textGrob("Variable 1", rot = -90, gp = gpar(col = gray(1)))),
                     4, 8, 6, name = paste(runif(2)))

# add label for top strip
z <- gtable_add_rows(z, unit(z$heights[[3]], 'cm'), 2)
z <- gtable_add_grob(z, 
                     list(rectGrob(gp = gpar(col = NA, fill = gray(0.5))),
                          textGrob("Variable 2", gp = gpar(col = gray(1)))),
                     3, 4, 3, 6, name = paste(runif(2)))

# add margins
z <- gtable_add_cols(z, unit(1/8, "line"), 7)
z <- gtable_add_rows(z, unit(1/8, "line"), 3)

# draw it
grid.newpage()
grid.draw(z)

Please would someone kindly point out to me the part of the code that's telling it how wide the general facet label should be?

Carter

You can get something with facet_grid(val.c + "Raphael" ~ "Donatello" + val.d), but to get a single overall strip label, you're probably going to have to hack it into place by drawing rectangles, unless you can break the constraints of the facetting labellers. Also, you need to add library(RColorBrewer) so the above code is reproducible. – Sideshow

Quick & dirty, i.e. without touching the underlying grid structures, maybe p <- ggplot(maya, aes(x=val.a, y=val.b)) + geom_point(shape=20,size=3, aes(colour=val.e)) + facet_grid(val.c~val.d) + xlab(NULL) + ylab(NULL) + scale_colour_gradientn(colours=brewer.pal(9,"YlGnBu"), name="Splinter") + theme(legend.position="bottom") and then gridExtra::grid.arrange(p, top = "Michaelangelo", right = "Leonardo"). – Achlamydeous

Unfortunately, neither is what I'm hoping for, although these two answers are quite useful. – Carter

@ReubenMathew I updated that answer you linked, try the code again – Entrails

rawr, I'm getting this for an error. Error in unit(z$width[[7]], "cm") : (list) object cannot be coerced to type 'double' – Carter

are you using your example? I copied your code and the answer and it works for me – Entrails

I am. I even tried copying your answer and running it, and I still get that error. – Carter

(Just a side note: the complexity you're encountering in making something that does this "more generally" is the main reason it isn't built into ggplot2. It's just too hard, given developer constraints.) – Lynnelle

Answer 1

This is fairly general. The current locations of the top and right strips are given in the layout data frame. This solution uses those locations to position the new strips. The new strips are constructed so that heights, widths, background colour, and font size and colour are the same as in current strips. There are some explanations below.

# Packages
library(ggplot2)
library(RColorBrewer)
library(grid)
library(gtable)

# Data
val.a <- rnorm(20)
val.b <- rnorm(20)
val.c <- c("A","B","C","D","E","F","G","H","I","J")
val.d <- c("A","B","C","D","E","F","G","H","I","J")
val.e <- rnorm(20)
maya <- data.frame(val.a,val.b,val.c,val.d,val.e)

# Base plot
p <- ggplot(maya, aes(x = val.a, y = val.b)) + 
   geom_point(shape = 20,size = 3, aes(colour = val.e)) + 
   facet_grid(val.c ~ val.d) + 
   xlab("Leonardo") + ylab("Michaelangelo") + 
   scale_colour_gradientn(colours = brewer.pal(9,"YlGnBu"), name = "Splinter")

# Labels 
labelR = "Variable 1"
labelT = "Varibale 2"

# Get the ggplot grob
z <- ggplotGrob(p)

# Get the positions of the strips in the gtable: t = top, l = left, ...
posR <- subset(z$layout, grepl("strip-r", name), select = t:r)
posT <- subset(z$layout, grepl("strip-t", name), select = t:r)

# Add a new column to the right of current right strips, 
# and a new row on top of current top strips
width <- z$widths[max(posR$r)]    # width of current right strips
height <- z$heights[min(posT$t)]  # height of current top strips

z <- gtable_add_cols(z, width, max(posR$r))  
z <- gtable_add_rows(z, height, min(posT$t)-1)

# Construct the new strip grobs
stripR <- gTree(name = "Strip_right", children = gList(
   rectGrob(gp = gpar(col = NA, fill = "grey85")),
   textGrob(labelR, rot = -90, gp = gpar(fontsize = 8.8, col = "grey10"))))

stripT <- gTree(name = "Strip_top", children = gList(
   rectGrob(gp = gpar(col = NA, fill = "grey85")),
   textGrob(labelT, gp = gpar(fontsize = 8.8, col = "grey10"))))

# Position the grobs in the gtable
z <- gtable_add_grob(z, stripR, t = min(posR$t)+1, l = max(posR$r) + 1, b = max(posR$b)+1, name = "strip-right")
z <- gtable_add_grob(z, stripT, t = min(posT$t), l = min(posT$l), r = max(posT$r), name = "strip-top")

# Add small gaps between strips
z <- gtable_add_cols(z, unit(1/5, "line"), max(posR$r))
z <- gtable_add_rows(z, unit(1/5, "line"), min(posT$t))

# Draw it
grid.newpage()
grid.draw(z)

Eaglet

Answer 2

FYI for those looking at this but hoping for a more streamlined implementation, you can achieve the same sort of outcome as Sandy Muspratt's using the facet_nested function from the ggh4x package.

# Packages
library(ggplot2)
library(ggh4x)
library(RColorBrewer)

# Data
val.a <- rnorm(20)
val.b <- rnorm(20)
val.c <- c("A","B","C","D","E","F","G","H","I","J")
val.d <- c("A","B","C","D","E","F","G","H","I","J")
val.e <- rnorm(20)
maya <- data.frame(val.a,val.b,val.c,val.d,val.e)

# plot
ggplot(maya, aes(x = val.a, y = val.b)) + 
  geom_point(shape = 20,size = 3, aes(colour = val.e)) + 
  facet_nested("Variable 2" * val.c ~ "Variable 1" * val.d) + 
  xlab("Leonardo") + ylab("Michaelangelo") + 
  scale_colour_gradientn(colours = brewer.pal(9,"YlGnBu"), name = "Splinter")

Bartholomeo