reshape a matrix
On Aug 20, 2011, at 1:21 PM, Uwe Ligges wrote:
On 20.08.2011 19:04, David Winsemius wrote:
On Aug 20, 2011, at 12:32 PM, Uwe Ligges wrote:
On 20.08.2011 17:04, Wendy wrote:
Hi all,
I have a data.frame like following
A<-c('d0','d0','d1','d1','d2','d2')
B<-rep(c('control','sample'),3)
C<-c(rep(100000,2),200,300,400,500)
dataframe<-data.frame(A,B,C)
I want to reshape the matrix, so the matrix with 'd0', 'd1' and
'd2'
in rows
and 'control' and 'sample' in columns. Is there a function for
doing
this
easily?
See ?reshape reshape(data=dataframe, idvar="A", timevar="B", direction="wide") Uwe Ligges
Many people have experienced problems understanding the mechanics of the base function 'reshape'. If you do not and if do continue to use it, you would be doing the world a great service by writing a tutorial manual with a bunch of worked examples. I have never found a tutorial that clarified how I should use it in the variety of situations where I have needed it.
David, I think there are some good examples on the help page. What is missing? What is not clearly explained?
The stumbling blocks I have encountered are in trying to figure out which of the multiple arguments are needed a) in going from wide to long and b) in going from long to wide, c) and what are the reasons for the various error messages I provoke . I am almost never able to do it correctly on the first try and rarely able to do it even on the fourth try. I bought Spector's book in hopes of understanding it better, but his efforts did not take root in my brain. In the instance above, how would I have know how to apply the help page description of timevar (below) to this problem? timevar the variable in long format that differentiates multiple records from the same group or individual. To my reading that does not distinguish the purpose of 'timevar' from the purpose of 'idvar' and then reading the 'idvar' definition just below it does not help at all.
David. > If a longer tutorial is needed, that may be an article for the R > Help Desk in The R Journal. Anybody volunteering? > > 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.) David Winsemius, MD West Hartford, CT