Unequal breaks and label lengths error when alpha (transparency) level not present in data

Question

In ggplot2 version 2.2.0, E.g.:

tmp_df <- data.frame(x = 1:3, y = 1:3, alpha = rep(0.5, 3))

#   x y alpha
# 1 1 1   0.5
# 2 2 2   0.5
# 3 3 3   0.5

ggplot(t         


        

Answer 1

You must supply the limits for the scale because tmp_df$alpha is always the same, and ggplot does not know the 'range' of the scale.

library(ggplot2)
tmp_df <- data.frame(x = 1:3, y = 1:3, alpha = rep(0.5, 3))
tmp_df
#>   x y alpha
#> 1 1 1   0.5
#> 2 2 2   0.5
#> 3 3 3   0.5

ggplot(tmp_df, aes(x, y, alpha = alpha)) +
    geom_bar(stat = 'identity') +
    scale_alpha(breaks = c(0.25, 0.5, 1), labels = c('a', 'b', 'c'), limits = c(0, 1))

If the alpha dimension has a range itself, limits are no longer necessary, but note the in the following example the first break is ignored, as it is outside the range. limits would again be necessary if you want to include it.

tmp_df <- data.frame(x = 1:3, y = 1:3, alpha = seq(.5, 1.5, .5))
tmp_df
#>   x y alpha
#> 1 1 1   0.5
#> 2 2 2   1.0
#> 3 3 3   1.5

ggplot(tmp_df, aes(x, y, alpha = alpha)) +
    geom_bar(stat = 'identity') +
    scale_alpha(breaks = c(0.25, 0.5, 1), labels = c('a', 'b', 'c'))