Use ggplot2 to plot data from a data.frame where the columns are S4 classes extending the class &quo-CodePudding

I defined the two classes

setClass("myDF", contains = "data.frame")
setClass("myCol", contains = "factor")

I then create two test data.frame

orig_df <- data.frame(A = factor(sample(c("1", "2"), size = 100, replace = T), levels = c("1", "2"), labels = c("Apple", "Banana")))
my_df <- new("myDF", data.frame(A = new("myCol", orig_df$A)))

When plotting a barplot using ggplot2, there are no bars when I use the data.frame containing the column of class myCol.

ggplot(orig_df, aes(x = A))    geom_bar(stat = "count")  # works fine

ggplot(my_df, aes(x = A))    geom_bar(stat = "count")  # no bars visible

It also works on an object of class myDF, which contains common factors as a column.

I struggle to figure out what I missed. Do I need to define a method for some generic (an accessor like [)?

R version 4.1.3 (2022-03-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19044)

Matrix products: default

locale:
[1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252    LC_MONETARY=German_Germany.1252
[4] LC_NUMERIC=C                    LC_TIME=German_Germany.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] ggplot2_3.3.6

loaded via a namespace (and not attached):
 [1] magrittr_2.0.3   tidyselect_1.1.2 munsell_0.5.0    colorspace_2.0-3 R6_2.5.1         rlang_1.0.2     
 [7] fansi_1.0.3      dplyr_1.0.9      tools_4.1.3      grid_4.1.3       gtable_0.3.0     utf8_1.2.2      
[13] cli_3.3.0        DBI_1.1.2        withr_2.5.0      ellipsis_0.3.2   digest_0.6.29    assertthat_0.2.1
[19] tibble_3.1.7     lifecycle_1.0.1  crayon_1.5.1     farver_2.1.0     purrr_0.3.4      vctrs_0.4.1     
[25] glue_1.6.2       labeling_0.4.2   compiler_4.1.3   pillar_1.7.0     generics_0.1.2   scales_1.2.0    
[31] pkgconfig_2.0.3

CodePudding user response：

A workaround is to make an explicit call to factor:

ggplot(my_df, aes(x = factor(A)))    geom_bar(stat = "count", width = 1, fill = "steelblue")

When udpated to R 4.2, it is working without it.