Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Max Kuhn
> Sent: Monday, December 06, 2010 8:35 AM
> To: r-help at r-project.org
> Subject: [R] less than full rank contrast methods
>
> I'd like to make a less than full rank design using dummy variables
> for factors. Here is some example data:
>
> when <- data.frame(time = c("afternoon", "night", "afternoon",
> "morning", "morning", "morning",
> "morning", "afternoon", "afternoon"),
> day = c("Monday", "Monday", "Monday",
> "Wednesday", "Wednesday", "Friday",
> "Saturday", "Saturday", "Friday"))
>
> For a single factor, I can do this this using
>
> > head(model.matrix(~time -1, data = when))
> timeafternoon timemorning timenight
> 1 1 0 0
> 2 0 0 1
> 3 1 0 0
> 4 0 1 0
> 5 0 1 0
> 6 0 1 0
>
> but this breakdown muti-variable formulas such as "time + day" or
> "time + dat + time:day".
>
> I've looked for alternate contrast functions to do this and I haven't
> figured out a way to coerce existing functions to get the desired
> output. Hopefully I haven't missed anything obvious.
>
> Thanks,
>
> Max
>
> > sessionInfo()
> R version 2.11.1 Patched (2010-09-11 r52910)
> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
>
> locale:
> [1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base
>
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