[R] Reshaping data

[Dimitris Rizopoulos]

just try

mymatrix <- matrix(0, 12, 10)
mymatrix[cbind(mydf$age, mydf$yr)] <- mydf$no
mymatrix


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Rau, Roland" <Rau at demogr.mpg.de>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, December 08, 2005 9:50 AM
Subject: [R] Reshaping data


> Dear all,
>
> given I have data in a data.frame which indicate the number of 
> people in
> a
> specific year at a specific age:
>
> n <- 10
> mydf <- data.frame(yr=sample(1:10, size=n, replace=FALSE),
>                   age=sample(1:12, size=n, replace=FALSE),
>                   no=sample(1:10, size=n, replace=FALSE))
>
> Now I would like to make a matrix with (in this simple example)
> 10 columns (for the years) and 12 rows (for the ages). In each cell,
> I would like to put the correct number of individuals.
>
> So far I was doing this as follows:
>
> mymatrix <- matrix(0, ncol=10, nrow=12)
> for (year in unique(mydf$yr)) {
>  for (age in unique(mydf$age)) {
>    if (length(mydf$no[mydf$yr==year & mydf$age==age]) > 0) {
>      mymatrix[age,year] <- mydf$no[mydf$yr==year & mydf$age==age]
>    } else {
>      mymatrix[age,year] <- 0
>    }
>  }
> }
>
> This is fairly fast in such a simple setting.
> But with more years and ages (and for roughly 300 datasets) this 
> becomes
> pretty slow. And in addition, this is not really elegant R-code.
>
> Can somebody point me into the direction how I can do that in a more
> elegant
> way, possibly avoiding the loops?
>
> Thanks,
> Roland
>
> +++++
> This mail has been sent through the MPI for Demographic 
> Rese...{{dropped}}
>
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