Hi: Here are two more candidates, using packages plyr and data.table. Your toy data frame is called dd below.
library(plyr) ddply(dd, .(Site, Prof), transform, Hadj = H - min(H)) Site Prof H Hadj 1 1 1 24 8 2 1 1 16 0 3 1 1 67 51 4 1 2 23 0 5 1 2 56 33 6 1 2 45 22 7 2 1 67 21 8 2 1 46 0 library(data.table) dt <- data.table(dd, key = 'Site, Prof') dt[, list(H = H, Hadj = H - min(H)), by = 'Site, Prof'] <same output as above> HTH, Dennis On Tue, May 3, 2011 at 8:44 AM, Woida71 <w.gost...@ipp.bz.it> wrote: > Hello everybody, > I am beginning with loops and functions and would be glad to have help in > the following question: > If i have a dataframe like this > Site Prof H > 1 1 24 > 1 1 16 > 1 1 67 > 1 2 23 > 1 2 56 > 1 2 45 > 2 1 67 > 2 1 46 > And I would like to create a new column that subtracts the minimum of H from > H, but for S1 and P1 > only the minimum of the data points falling into this category should be > taken. > So for example the three first numbers of the new column write: 24-16, > 16-16, 67-16 > the following numbers refering to Site1 and Prof2 write: 23-23, 56-23, > 45-23. > I think with two loops one refering to the Site, the other to the Prof, it > should be possible to automatically > create the new column. > Thanks a lot for any help. > > -- > View this message in context: > http://r.789695.n4.nabble.com/Simple-loop-tp3492819p3492819.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > 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. > ______________________________________________ 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.
