From: Florence Combes <fcombes_at_gmail.com>

Date: Fri 07 Oct 2005 - 00:20:08 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Oct 07 00:40:57 2005

Date: Fri 07 Oct 2005 - 00:20:08 EST

> > > 2d I can't manage to deal with factors, so when I have some, I

*> transform
**> > > them in vectors (with levels()), but I think I miss the power and
**> utility
**> > of
**> > > the factor type ?
**> >
**> > levels() is not the conversion you want.
*

in fact I use

'as.numeric(levels(f))[f]'

(from the ?factor description)

That lists all the levels, but

> > it doesn't tell you how they correspond to individual observations. For

*> > example,
**> >
**> > > df <- data.frame(x=1:3, y=c('a','b','a'))
**> > > df
**> > x y
**> > 1 1 a
**> > 2 2 b
**> > 3 3 a
**> > > levels(df$y)
**> > [1] "a" "b"
**> >
**> > If you need to convert back to character values, use as.character():
**> >
**> > > as.character(df$y)
**> > [1] "a" "b" "a"
*

got it.

> > 1. You can't compare the levels of a factor unless you declared it to

*> > be ordered:
**> >
**> > > df$y[1] > df$y[2]
**> > [1] NA
**> > Warning message:
**> > > not meaningful for factors in: Ops.factor(df$y[1], df$y[2])
**> >
**> > but
**> >
**> > > df$y <- ordered(df$y)
**> > > df$y[1] > df$y[2]
**> > [1] FALSE
**> >
**> > However, you need to watch out here: the comparison is done by the order
**> > of the factors
*

I am sorry I don't understand this.

here you compare the position of a in the factor and the position of b in
the factor ?

, not an alphabetic comparison of their names:

*> >
*

> > > levels(df$y) <- c("before", "after")

*> > > df
**> > x y
**> > 1 1 before
**> > 2 2 after
**> > 3 3 before
**> > > df$y[1] > df$y[2]
*** > > [1] FALSE
**
best regards,

[[alternative HTML version deleted]]

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Oct 07 00:40:57 2005

*
This archive was generated by hypermail 2.1.8
: Fri 03 Mar 2006 - 03:40:38 EST
*