Inconsistent facet labeller behaviour when using characters to facet

[naught101]

library(data.table)
library(ggplot2)

# Labeller function
iris_lblr <- function(var, value) {
    labels <- c('setosa'='SET', 'versicolor'='VERS', 'virginica'='VIRG')
        if (var=='Species') {
            return ( labels[value])
        }
}

# using data.table just for ease of filtering/mutation
dt <- data.table(iris)

# This plot works fine - short caps labels are applied correctly
ggplot(dt, aes(x=Sepal.Length, y=Petal.Length)) + geom_point() + facet_grid(.~Species, labeller=iris_lblr)

# this plot also has the correct CAPS labels applied, and the middle facet is missing
ggplot(dt[Species!='versicolor'], aes(x=Sepal.Length, y=Petal.Length)) + geom_point() + facet_grid(.~Species, labeller=iris_lblr)

dt[, Species:=as.character(Species)]

# This plot shows "VERS" where it should show "VIRG". 
ggplot(dt[Species!='versicolor'], aes(x=Sepal.Length, y=Petal.Length)) + geom_point() + facet_grid(.~Species, labeller=iris_lblr)

[hadley]

Could you please create a minimal reprex without data table?

[naught101]

library(dplyr)
library(ggplot2)

# Labeller function
iris_lblr <- function(var, value) {
    labels <- c('setosa'='SET', 'versicolor'='VERS', 'virginica'='VIRG')
    if (var=='Species') {
        return ( labels[value])
    }
}

# This plot works fine - short caps labels are applied correctly
ggplot(iris, aes(x=Sepal.Length, y=Petal.Length)) + geom_point() + facet_grid(.~Species, labeller=iris_lblr)

# this plot also has the correct CAPS labels applied, and the middle facet is missing
ggplot(iris %>% filter(Species!='versicolor'), aes(x=Sepal.Length, y=Petal.Length)) + geom_point() + facet_grid(.~Species, labeller=iris_lblr)

df <- iris %>% mutate(Species=as.character(Species))

# This plot shows "VERS" where it should show "VIRG". 
ggplot(df %>% filter(Species!='versicolor'), aes(x=Sepal.Length, y=Petal.Length)) + geom_point() + facet_grid(.~Species, labeller=iris_lblr)

[hadley]

Hmmm, that's because value is a factor, not a character vector, as you expect. I'm probably missing a stringsAsFactors = FALSE somewhere.