[R] reshape a matrix

[Uwe Ligges]

On 21.08.2011 12:54, Michael Dewey wrote:
> 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.

In think tha major problem is that stuff like "id" and "time" etc. may 
be misleading, if they do not fit to the context. Don't believe I do 
things correct right away here. Nevertheless, improving the wording of 
the reshape() documentation is not easy at all if we want to be precise. 
Maybe we find another volunteer or I find some time to write a short 
column for the next issue of The R Journal.

Best wishes,
Uwe



>> 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
>