On Nov 1, 2009, at 3:51 PM, Kevin E. Thorpe wrote:
I'm sure this is simple enough, but an R site search on my subject
terms did suggest a solution. I have a numeric vector with many
values that I wish to create a factor from having only a few levels.
Here is a toy example.
> x <- 1:10
> x <-
factor
(x,levels=1:10,labels=c("A","A","A","B","B","B","C","C","C","C"))
You have thusly created a pathological situation. In 2.10.0 this is
what you might see:
> x <-
factor(x,levels=1:10,labels=c("A","A","A","B","B","B","C","C","C","C"))
Warning message:
In `levels<-`(`*tmp*`, value = c("A", "A", "A", "B", "B", "B", "C", :
duplicated levels will not be allowed in factors anymore
What you _should_ have done was:
x2 <- factor(c("A","A","A","B","B","B","C","C","C","C"))
The usual approach to getting rid of unused factor levels is just to
apply the function factor() again without additional arguments.
> x <- factor(x) # the "x" was from your code
Warning message:
In `levels<-`(`*tmp*`, value = c("A", "A", "A", "B", "B", "B", "C", :
duplicated levels will not be allowed in factors anymore
# but that will be the last time you will see the warning..
> summary(x)
A B C
3 3 4
--
David.
> x
[1] A A A B B B C C C C
Levels: A A A B B B C C C C
> summary(x)
A A A B B B C C C C
3 0 0 3 0 0 4 0 0 0
So, there are clearly still 10 underlying levels. The results I would
like to see from printing the value and summary(x) are:
> x
[1] A A A B B B C C C C
Levels: A B C
> summary(x)
A B C
3 3 4
Hopefully this makes sense.
Thanks,
Kevin
--
Kevin E. Thorpe
Biostatistician/Trialist, Knowledge Translation Program
Assistant Professor, Dalla Lana School of Public Health
University of Toronto
email: kevin.tho...@utoronto.ca Tel: 416.864.5776 Fax: 416.864.3016
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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