I have to confess that plyr has made me lazy about remembering tapply, by, aggregate et al., so I'm no help there. But if you want to use plyr it's just
ddply(dat, .(V1), summarize, cor.v2.v3 = cor(V2, V3)) Best, Ista On Wed, Jun 15, 2011 at 10:31 AM, jfdawson <j.f.daw...@aston.ac.uk> wrote: > I'm hoping there is a simple answer to this - it seems that there should be, > but I can't figure it out. > > I have a matrix/data frame with three variables of interest - V1, V2, V3. > One, V1, is a factor with x levels (x may be a large number); I want to > calculate the correlation between the other two (i.e. cor(V2,V3)) for each > level, and store it as a vector of length x. > > I should think this should be possible using a function like tapply, but I > cannot work out what the syntax would be - everything I have tried produces > either an error, or just repeats the correlations between V2 & V3 on the > whole matrix. > > Could anyone suggest what I should be doing? > > Many thanks, > Jeremy > > -- > View this message in context: > http://r.789695.n4.nabble.com/Correlations-by-subgroups-tp3599548p3599548.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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.
