[R] removed data is still there!

[ONKELINX, Thierry]

Removing elements from a factor does not change the levels of the
factor.

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium

tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey
  

> -----Oorspronkelijk bericht-----
> Van: r-help-bounces op r-project.org 
> [mailto:r-help-bounces op r-project.org] Namens pdb
> Verzonden: dinsdag 21 september 2010 13:42
> Aan: r-help op r-project.org
> Onderwerp: [R] removed data is still there!
> 
> 
> I'm confused, hope someone can point out what is not obvious to me.
> 
> I thought I was creating a new data frame by 'deleting' rows 
> from an existing dataframe - I've tried 2 methods.
> 
> But this new data frame seems to remember values from its 
> parent - even though there are no occurences.  
> 
> Where does it get the values versicolor  and virginica from 
> and give then a count of 0?
> 
> What am I missing?
> 
> Thanks in advance. 
> 
> > summary(iris$Species)
>     setosa versicolor  virginica 
>         50         50         50 
> 
> > nrow(iris)
> [1] 150
> 
> > iris1 <- iris[iris$Species == 'setosa',]
> 
> > nrow(iris1)
> [1] 50
> 
> > summary(iris1$Species)
>     setosa versicolor  virginica 
>         50          0          0 
> 
> boxplot(Petal.Width ~ Species, data = iris1, plot=1)
> 
> > iris2 <- subset(iris, Species == 'setosa')
> 
> > nrow(iris2)
> [1] 50
> 
> > summary(iris2$Species)
>     setosa versicolor  virginica 
>         50          0          0 
> 
> > boxplot(Petal.Width ~ Species, data = iris2, plot=1)
> 
> 
> 
> 
> --
> View this message in context: 
> http://r.789695.n4.nabble.com/removed-data-is-still-there-tp25
> 48440p2548440.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help op 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
> and provide commented, minimal, self-contained, reproducible code.
> 

Druk dit bericht a.u.b. niet onnodig af.
Please do not print this message unnecessarily.

Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer 
en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is
door een geldig ondertekend document. The views expressed in  this message 
and any annex are purely those of the writer and may not be regarded as stating 
an official position of INBO, as long as the message is not confirmed by a duly 
signed document.