[R] bug with subset and plot?

[Erik Iverson]

http://stackoverflow.com/questions/1195826/dropping-factor-levels-in-a-subsetted-data-frame-in-r

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Knut Helge Jensen
Sent: Friday, August 07, 2009 5:02 AM
To: r-help at stat.math.ethz.ch
Subject: [R] bug with subset and plot?

Hi!

I have the following problem that I beleive is a bug:

I have a dataframe with one categorical and one numerical vector. The 
categorical vector has three levels (uc, up and vc). A plot of the 
vectors with the categorical vector on the x-axis gives a boxplot with 
three boxes - exactly as expected.

If I then use the subset function to make a dataset that only includes 
two of the levels of the categorical vector and do the plot again, all 
three levels are still shown on the x-axis even though one of them 
doesn't exist in the dataset. The plot shows correct number of boxes (2).

The whole syntax for what I describe is as follows:
exploration.df <- read.table('clipboard', header=T)
attach(exploration.df)
plot(treatment,total.escapes)

exp.df <- subset(exploration.df, treatment!='up')
attach(exp.df)
plot(treatment, total.escapes)

I use R version 2.9.1 (2009-06-26) for Debian.

Knut Helge Jensen