[R] help with colsplit (reshape)

[Ista Zahn]

Thanks Hadley, with your help I'm getting things figured out.
On Jun 13, 2008, at 2:09 PM, hadley wickham wrote:

>> M.Data2 <- data.frame(M.Data, colsplit(M.Data$variable, split = "\ 
>> \.", names
>> = c("treatment", "time")))
>>
>> which gave:
>>
>> head(M.Data2)
>> pid variable value treatment  time
>> 1   1    predA    -1     predA predA
>> 2   2    predA    -2     predA predA
>> 3   3    predA    -1     predA predA
>> 4   4    predA    -2     predA predA
>> 5   5    predA    -1     predA predA
>> 6   6    predA    -2     predA predA
>>
>> Closer but no cigar.
>
> Have a look at the whole thing - it's getting it right most of the
> time.  Going back to the original variable names, I see that "PredA"
> does not have a time associated with it.  What do you expect the time
> to be?
Right, there is no time associated with this variable. So I tried  
again, treating it as an id:

M.Data <- melt(Data, id = c("pid", "predA"))

 From here I was able to achieve the desired result, as follows:

M.Data <- data.frame(M.Data, colsplit(M.Data$variable, split = "\\.",  
names=c("measure", "time")))
M.Data$variable <- M.Data$measure
M.Data <- M.Data[-5]
L.Data <- cast(M.Data, ... ~ variable)

This is perhaps a bit inelegant but it works! I'm interested in  
knowing if there is a better way to do it, but I'm happy that I've at  
least figured out this much. As always I'm humbled by the generosity  
of people who not only make their software available but also take the  
time to answer questions on this list. Thank you!

-Ista
>
>
>> I would be grateful if someone will tell me (a) how to reshape the  
>> data as
>> described above using the reshape package, (b) what difference  
>> between split
>> = "." and split = "\\." is,
>
> The splitting argument is a regular expression, and in regular
> expression speak "." means to match any one character.  "\\." escapes
> the full stop, so it only matches full stops.
>
>> and (c) if more information about the colsplit
>> command is available anywhere.
>
> Probably the best way is just to look at the code (it's pretty  
> simple):
>
>> colsplit.character
> function (x, split = "", names)
> {
>   vars <- as.data.frame(do.call(rbind, strsplit(x, split)))
>   names(vars) <- names
>   as.data.frame(lapply(vars, function(x)  
> type.convert(as.character(x))))
> }
>
> If strsplit doesn't do what you want, you might need to write your own
> function following those lines.
>
> Hadley
>
> -- 
> http://had.co.nz/