example(factor)

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

will get you what you need.


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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