reshape a matrix
At 18:21 20/08/2011, Uwe Ligges wrote:
On 20.08.2011 19:04, David Winsemius wrote:
On Aug 20, 2011, at 12:32 PM, Uwe Ligges wrote:
[snip original problem]
David, I think there are some good examples on the help page. What is missing? What is not clearly explained? If a longer tutorial is needed, that may be an article for the R Help Desk in The R Journal. Anybody volunteering?
Uwe I think the problem is that those of us who do not understand are in such a state of ignorance that we do not know what it is that we do not understand. I have resigned myself to the realisation that there are a very small number of things about R which I shall never understand and always solve by trial and error and the parameterisation of reshape is the leading example (closely followed by backslashes). I do not think the writers of the documentation are at fault here, it is either just inherently difficult to understand or my cortex is wired up inappropriately.
Best, Uwe
So Hadley wrote an alternate facility ... the reshape package that does not have a reshape function in it but rather two functions 'melt' and 'cast'. Your data is all ready "molten", i.e. it is in the long format (in the terminology of the base reshape function) with identifier values in each row and a single column of values.
> library(reshape) > cast(dataframe,A~B)
Using C as value column. Use the value argument to cast to override this choice A control sample 1 d0 1e+05 1e+05 2 d1 2e+02 3e+02 3 d2 4e+02 5e+02 Basically the cast formula keeps the LHS variables in the rows and hte RHD variables get arranges in columns. (For reasons that are unclear to me the dataframe argument was placed first when using positional argument passing, unlike most other formula methods in R.)
Michael Dewey info at aghmed.fsnet.co.uk http://www.aghmed.fsnet.co.uk/home.html