Using facet tags and strip labels together in ggplot2

Question

I\'d like to create a figure using ggplot2\'s facet_grid, like below:

# Load ggplot2 librar         


        

Answer 1

Of course, I find a solution immediately after asking. The problem appears to be that tag_facet sets strip labels to element_blank, which can be fixed by calling theme after calling tag_facet.

# Load libraries
library(ggplot2)
library(egg)
#> Warning: package 'egg' was built under R version 3.5.3
#> Loading required package: gridExtra

# Create plot
p <- ggplot(mtcars, aes(mpg, wt)) 
p <- p + geom_point() 
p <- p + facet_grid(gear ~ cyl)
p <- tag_facet(p)
p <- p + theme(strip.text = element_text())
print(p)

^{Created on 2019-05-09 by the reprex package (v0.2.1)}

Answer 2

You can view the code for tag_facet here. As you can see, the function explicitly and deliberately removes the facet strips (see also the "value" in the documentation). You can fix that by creating your own function, and just removing the theme call from the original code:

tag_facet2 <- function(p, open = "(", close = ")", tag_pool = letters, x = -Inf, y = Inf, 
    hjust = -0.5, vjust = 1.5, fontface = 2, family = "", ...) {

    gb <- ggplot_build(p)
    lay <- gb$layout$layout
    tags <- cbind(lay, label = paste0(open, tag_pool[lay$PANEL], close), x = x, y = y)
    p + geom_text(data = tags, aes_string(x = "x", y = "y", label = "label"), ..., hjust = hjust, 
        vjust = vjust, fontface = fontface, family = family, inherit.aes = FALSE)
}

Answer 3

This can be done using only geom_text() :

data_text <- data.frame(
  cyl   = c(4, 6, 8, 4, 6, 8, 4, 6, 8),
  gear  = c(3, 3, 3, 4, 4, 4, 5, 5, 5)
  label = c('(a)', '(b)', '(c)', '(d)', '(e)', '(f)', '(g)', '(h)', '(i)')
)

ggplot(mtcars, aes(mpg, wt)) +
geom_point() +
facet_grid(gear ~ cyl) +
geom_text(data=data_text, aes(x=12, y=5, label=label), fontface='bold', size=4)

Answer 4

With {tagger} package, this can be made a little simpler. You can install tagger by using devtools::install_github("eliocamp/tagger"). After installing tagger, let's load it.

library(tagger)
library(ggplot2)

# Plot dummy data
p <- ggplot(mtcars, aes(mpg, wt)) 
p <- p + geom_point() 
p + facet_grid(gear ~ cyl) + tag_facets()