Douglas Bates wrote:
On Wed, Sep 30, 2009 at 2:42 PM, Douglas Bates <ba...@stat.wisc.edu> wrote:
On Wed, Sep 30, 2009 at 2:43 AM, Dieter Menne
<dieter.me...@menne-biomed.de> wrote:
Dear List,
creating factors in a given non-default orders is notoriously difficult to
explain in a course. Students love the ifelse construct given below most,
but I remember some comment from Martin Mächler (?) that ifelse should be
banned from courses.
Any better idea? Not necessarily short, easy to remember is important.
Dieter
data = c(1,7,10,50,70)
levs = c("Pre","Post")
# Typical C-Programmer style
factor(levs[as.integer(data >10)+1], levels=levs)
# Easiest to understand
factor(ifelse(data <=10, levs[1], levs[2]), levels=levs)
Why not
factor(data > 10, labels = c("Pre", "Post"))
[1] Pre Pre Pre Post Post
Levels: Pre Post
All you have to remember is that FALSE comes before TRUE.
And besides, Frank Harrell will soon be weighing in to tell you why
you shouldn't dichotomize in the first place.
And someone might also remind you that it is safest to include
levels=c(FALSE,TRUE), just in case the condition is always TRUE. (Terry
Thernau has the scars from the implementation of Surv()...)
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907
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