data manipulation involving aggregate

as.data.frame.table(xtabs(area ~ habitat + sq, DF), responseName = "area.sum")[c(2:3, 1)]

hi all,

I often have a data frame like this example

data.frame(sq=c(1,1,1,2,2,3,3,3,3),area=c(1,2,3,1,2,3,1,2,3),habitat=c("garden","garden","pond","field","garden","river","garden","field","field"))

for each "sq" I have multiple "habitat"s each with an associated "area".

I want to aggregate the data frame so that for each "sq" I have a column of all possible "habitat"s and another column for the calculation of the summed areas for each "habitat". If a certain habitat doesnt exist in that square I want a zero, like this..

data.frame(sq=rep(seq(1:3),each=4),area.sum=c(3,3,0,0,2,0,1,0,1,0,5,3),habitat=rep(c("garden","pond","field","river") ))

Is there an eloquent, efficient way of doing this? My solution involves lots of intermediate aggregated data frames, one for each habitat, then a series of merges onto a bigger data frame.

Thanks peeps and have a good weekend,

Simon.





Dr. Simon Pickett
Research Ecologist
Land Use Department
Terrestrial Unit
British Trust for Ornithology
The Nunnery
Thetford
Norfolk
IP242PU
01842750050

? ? ? ?[[alternative HTML version deleted]]