`scale_colour_manual()` does not drop factor levels missing in data

[aphalo]

Argument passed to formal parameter drop is ignored, and unused factor levels are not dropped from the legend as indicated in the documentation. This used to work in the past. 3.3.6, 3.3.5, 3.3.4 are broken, 3.3.3 is good.

Reprex for version 3.3.6 (3.3.5, 3.3.4). drop = TRUE ignored in the manual scale, but obeyed by the default scale.

library(ggplot2)
packageVersion("ggplot2")
#> [1] '3.3.6'

my.df <- data.frame(x = rnorm(50),
                    y = rnorm(50),
                    outcome = factor(sample(letters[1:3], 50, replace = TRUE), 
                                     levels = letters[1:4]))

# level "d" is dropped
ggplot(my.df, aes(x, y, colour = outcome)) +
  geom_point()

# level "d" is not dropped
ggplot(my.df, aes(x, y, colour = outcome)) +
  geom_point() +
  scale_colour_manual(values = c(a = "red", b = "green", c = "blue", d = "orange"),
                      drop = TRUE)

^{Created on 2022-09-04 with reprex v2.0.2}

Reprex for version 3.3.3. drop = TRUE obeyed consistently.

library(ggplot2)
packageVersion("ggplot2")
#> [1] '3.3.3'

my.df <- data.frame(x = rnorm(50),
                    y = rnorm(50),
                    outcome = factor(sample(letters[1:3], 50, replace = TRUE), 
                                     levels = letters[1:4]))

# level "d" is dropped
ggplot(my.df, aes(x, y, colour = outcome)) +
  geom_point()

# level "d" is dropped as expected
ggplot(my.df, aes(x, y, colour = outcome)) +
  geom_point() +
  scale_colour_manual(values = c(a = "red", b = "green", c = "blue", d = "orange"),
                      drop = TRUE)

^{Created on 2022-09-04 with reprex v2.0.2}

[smouksassi]

related to #4723
and I think this has been fixed in the dev version:

library(ggplot2)

set.seed(13465)
my.df <- data.frame(x = rnorm(50),
                    y = rnorm(50),
                    outcome = factor(sample(letters[1:3], 50,
                                            replace = TRUE), 
                                     levels = letters[1:4]))


ggplot(my.df, aes(x, y, colour = outcome)) +
  geom_point() +
  scale_colour_manual(values = c(a = "red" , b = "green",
                                 c = "blue", d = "orange"),
                      drop = TRUE)

packageVersion("ggplot2")
#> [1] '3.3.6.9000'

^{Created on 2022-09-04 with reprex v2.0.2}

[yutannihilation]

Yes, I think so, too. Please wait for the next release.

[aphalo]

o.k., great! I tried to install the development version before reporting, but the installation of one of the dependencies not yet in CRAN failed repeatedly. I should not have given up so quickly!