[R] Faceted bar plot shows wrong counts (ggplot2)

[Helios de Rosario]

I have encountered a problem with faceted bar plots. I have tried to
create something like the example explained in the ggplot2 book (see pp.
126-128):

library(ggplot2)
mpg4  <-  subset(mpg,  manufacturer  %in%
c("audi",  "volkswagen",  "jeep"))
mpg4$manufacturer  <-  as.character(mpg4$manufacturer)
mpg4$model  <-  as.character(mpg4$model)

base  <-  ggplot(mpg4,  aes(fill  =  model))  +
geom_bar(position  =  "dodge")  +
opts(legend.position  =  "none")
base  +  aes(x  =  model)  +
facet_grid(.  ~  manufacturer)

That example works fine; the bar heights are just the same as the
counts in the table:

table(mpg4[,1:2])
          model
manufacturer a4 a4 quattro a6 quattro grand cherokee 4wd gti jetta new
beetle
  audi        7          8          3                  0   0     0     
    0
  jeep        0          0          0                  8   0     0     
    0
  volkswagen  0          0          0                  0   5     9     
    6
          model
manufacturer passat
  audi            0
  jeep            0

But in other cases this does not occur. For instance, take a small
subset of data(diamonds):

diamonds25 <- droplevels(diamonds[1:25,2:3])
table(diamonds25)
           color
cut         E F H I J
  Fair      1 0 0 0 0
  Good      1 0 0 1 4
  Very Good 1 0 3 1 4
  Premium   3 1 0 1 0
  Ideal     1 0 0 1 2

And change the variables mapped in the previous plot:

base  <-  ggplot(diamonds25,  aes(fill  =  cut))  +
geom_bar(position  =  "dodge")  +
opts(legend.position  =  "none")
base  +  aes(x  =  cut)  +
facet_grid(.  ~  color)

I see all bars with height = 1.
I have ovserved this problem (wrong bar heights, but not always = 1),
in other cases when all counts are very small or zero.
What's wrong here?

Regards,
Helios

sessionInfo()
R version 2.14.2 (2012-02-29)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=Spanish_Spain.1252  LC_CTYPE=Spanish_Spain.1252
[3] LC_MONETARY=Spanish_Spain.1252 LC_NUMERIC=C
[5] LC_TIME=Spanish_Spain.1252

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

other attached packages:
[1] ggplot2_0.9.0

loaded via a namespace (and not attached):
 [1] colorspace_1.1-1   dichromat_1.2-4    digest_0.5.1      
grid_2.14.2
 [5] MASS_7.3-17        memoise_0.1        munsell_0.3       
plyr_1.7.1
 [9] proto_0.3-9.2      RColorBrewer_1.0-5 reshape2_1.2.1    
scales_0.2.0
[13] stringr_0.6



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