On Fri, 24 Sep 2010, Prof Brian Ripley wrote:

On Thu, 23 Sep 2010, Peter Ehlers wrote:

On 2010-09-21 5:51, Nikhil Kaza wrote:
example(factor)

iris1$Species<- factor(iris1$Species, drop=T)

will get you what you need.

Hmm, doesn't work for me. ?factor does not list a 'drop='
argument.

I suspect

iris1$Species <- [iris1$Species, drop=TRUE]

I don't know what happened there:

iris1$Species <- iris1$Species[, drop=TRUE]

is what I saw before sending.


was meant.  See ?`[.factor` .


 -Peter Ehlers



Nikhil Kaza
Asst. Professor,
City and Regional Planning
University of North Carolina

nikhil.l...@gmail.com

On Sep 21, 2010, at 7:41 AM, pdb wrote:


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)




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--
Brian D. Ripley,                  rip...@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

______________________________________________
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
and provide commented, minimal, self-contained, reproducible code.


--
Brian D. Ripley,                  rip...@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

______________________________________________
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
and provide commented, minimal, self-contained, reproducible code.

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