On Wed, 4 May 2005, Sean Davis wrote: > see ?aggregate.
Or maybe tapply, or its close relative, by: > by(df, list(df$station, df$date), function(x) + x$row[which.max(x$chlorophyll)]) : Ancona : 21/06/01 [1] NA ------------------------------------------------------------ : Castagneto : 21/06/01 [1] 3 ------------------------------------------------------------ : Ancona : 23/06/01 [1] 6 ------------------------------------------------------------ : Castagneto : 23/06/01 [1] NA since happily a row ID column was included in the data frame. Note that which.max only reports the row of the first maximum if there are ties. > > Sean > > On May 4, 2005, at 11:43 AM, alessandro carletti wrote: > > > Sorry for disturbing you with another newbie question! > > I have a data frame about coastal waters quality > > parameters: for some parameters (e.g. NH3) I have only > > 1 observation for each sampling station and each > > sampling date, while in other cases (chlorophyll) I > > have 1 obs for each meter-depth for each station and > > date. How can I select only the max chlorophyll value > > for each station/date? > > > > example > > > > row station date depth chlorophyll > > 1 Castagneto 21/06/01 -0.5 2.0 > > 2 Castagneto 21/06/01 -1.5 2.2 > > 3 Castagneto 21/06/01 -2.5 2.4 > > 4 Castagneto 21/06/01 -3.5 2.1 > > 5 Ancona 23/06/01 -0.5 2.4 > > 6 Ancona 23/06/01 -1.5 2.5 > > 7 Ancona 23/06/01 -2.5 2.2 > > 8 Ancona 23/06/01 -3.5 2.1 > > 9 Ancona 23/06/01 -4.5 1.9 > > ... > > > > I'd like to select only row 3 and 6, the ones with max > > chlorophyll values, or have the mean for the rows 1:4 > > and 5:9 > > > > Thanks > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! > > http://www.R-project.org/posting-guide.html > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > -- Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: [EMAIL PROTECTED] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
