R help - Aug 2009 - 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

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

See
http://wiki.r-project.org/rwiki/doku.php?id=tips:data-manip:drop_unused_levels

-Ista
> 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

hi knut

may be:

treatment<-factor(treatment)
plot(...)

cheers
milton
On Fri, Aug 7, 2009 at 6:02 AM, Knut Helge Jensen
<knut.jensen@bio.uib.no>wrote:
> 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
>
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
>
http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
>
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