On Mon, Dec 22, 2008 at 3:51 PM, Ranney, Steven <steven.ran...@montana.edu> wrote: > All - > > I have data that looks like > > psd Species Lake Length Weight St.weight Wr > Wr.1 vol > 432 substock SMB Clear 150 41.00 0.01 95.12438 > 95.10118 0.0105 > 433 substock SMB Clear 152 39.00 0.01 86.72916 > 86.70692 0.0105 > 434 substock SMB Clear 152 40.00 3.11 88.95298 > 82.03689 3.2655 > 435 substock SMB Clear 159 48.00 0.04 92.42095 > 92.34393 0.0420 > 436 substock SMB Clear 159 48.00 0.01 92.42095 > 92.40170 0.0105 > 437 substock SMB Clear 165 47.00 0.03 80.38023 > 80.32892 0.0315 > 438 substock SMB Clear 171 62.00 0.21 94.58105 > 94.26070 0.2205 > 439 substock SMB Clear 178 70.00 0.01 93.91912 > 93.90571 0.0105 > 440 substock SMB Clear 179 76.00 1.38 100.15760 > 98.33895 1.4490 > 441 S-Q SMB Clear 180 75.00 0.01 97.09330 > 97.08035 0.0105 > 442 S-Q SMB Clear 180 92.00 0.02 119.10111 > 119.07522 0.0210 > ... > [truncated] > > where psd and lake are categorical variables, with five and four > categories, respectively. I'd like to find the maximum vol and the > lengths associated with each maximum vol by each category by each lake. > In other words, I'd like to have a data frame that looks something like > > Lake Category Length vol > Clear substock 152 3.2655 > Clear S-Q 266 11.73 > Clear Q-P 330 14.89 > ... > Pickerel substock 170 3.4965 > Pickerel S-Q 248 10.69 > Pickerel Q-P 335 25.62 > Pickerel P-M 415 32.62 > Pickerel M-T 442 17.25 > > > In order to originally get this, I used > > with(smb[Lake=="Clear",], tapply(vol, list(Length, psd),max)) > with(smb[Lake=="Enemy.Swim",], tapply(vol, list(Length, psd),max)) > with(smb[Lake=="Pickerel",], tapply(vol, list(Length, psd),max)) > with(smb[Lake=="Roy",], tapply(vol, list(Length, psd),max)) > > and pulled the values I needed out by hand and put them into a .csv. > Unfortunately, I've got a number of other data sets upon which I'll need > to do the same analysis. Finding a programmable alternative would > provide a much easier (and likely less error prone) method to achieve > the same results. Ideally, the "Length" and "vol" data would be in a > data frame such that I could then analyze with nls. > > Does anyone have any thoughts as to how I might accomplish this?
You might want to have a look at the plyr package, http://had.co.nz/plyr, which provides a set of tools to make tasks like this easy. The are a number of similar examples in the introductory pdf that should get you started. Regards, Hadley -- http://had.co.nz/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
