The unstack function is a bit clumsy for this problem:
library(MASS)
cbind(Treatment = unstack(Rabbit, Treatment ~ Animal)[,1],
Dose = unstack(Rabbit, Dose ~ Animal)[,1],
unstack(Rabbit, BPchange ~ Animal))
A much better choice would be to use the reshape package:
require(reshape)
recast(Rabbit, Treatment + Dose ~ Animal, measure.var="BPchange")
Kevin Wright
On Sun, Nov 15, 2009 at 1:34 PM, Tariq Perwez <tariq.per...@gmail.com>wrote:
> Hi Everyone,
>
> I am trying to understand the unstack() function but after struggling for
> two days, I have given up. More specifically, I am trying the exercises at
> the end of Chapter 1 of Data Analysis and Graphics Using R by Maindonald
> and Braun, 2nd ed. Exercise 18 (p. 41) asks to unstack the Rabbit data
> frame
> from the MASS package to get a certain data frame that is shown in the
> exercise. Authors suggest to use the unstack() three times but I am so new
> to R that I have absolutely no clue as to what is to be done each of those
> times. Sadly for me, the help page for unstack() does not give much help
> either. For example, the statement in the help page regarding the argument
> form, "a two-sided formula whose left side evaluates to the vector to be
> unstacked and whose right side evaluates to the indicator of the groups to
> create" is very cryptic to me. Basically, I have tried things like:
>
> unstack(Rabbit, Dose ~ Animal)
>
> but notice that what I get is a data frame in which other columns of the
> Rabbit data frame disappear. I would appreciate if someone could help me
> understand this function. On page 17 of the same book, there is an example
> of unstack() function but that one uses a very simple data frame (only two
> columns). I would like to know how to handle more complex data frames as in
> the exercise. BTW, this is not a school assignment; I am learning R using
> this book on my own. Thanks for any help. Regards,
>
> Tariq
>
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>
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>
--
Kevin Wright
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