Hi I am not sure what you want to do as you speak about using different function for different part of your data.
> head(data) city year sex V 1 1 1975 F 25.3044 2 1 1975 M 16.5711 3 1 1976 M 16.6072 4 1 1976 F 24.2841 5 1 1977 M 14.8838 6 1 1977 F 24.8124 If it was only correlation coefficients you could use lapply split construction like lapply(split(data[,c(4,2)], interaction(data$city, data$sex)), function(x) summary(lm(x))$r.sq) $`1.M` [1] 0.923669 $`2.M` [1] 0.5151131 $`1.F` [1] 0.823817 $`2.F` [1] 0.7483883 or > lapply(split(data[,c(4,2)], interaction(data$city, data$sex)), cor) $`1.M` V year V 1.000000 -0.961077 year -0.961077 1.000000 $`2.M` V year V 1.0000000 -0.7177138 year -0.7177138 1.0000000 Regards Petr Pikal [EMAIL PROTECTED] 724008364, 581252140, 581252257 [EMAIL PROTECTED] napsal dne 14.05.2008 11:46:02: > Hallo All, > > I have difficulties understanding how factors work in R. Suppose a have > data in the panel form below. I would to compute a correlation coefficient > (actually apply a different function of two time series) in the V variable > between members of the two sexes in each city over time. How can this be > done? > > Thank you in advance, > Serguei > > city, year, sex, V > 1, 1975, 1, 25.3044 > 1, 1975, 0, 16.5711 > 1, 1976, 0, 16.6072 > 1, 1976, 1, 24.2841 > 1, 1977, 0, 14.8838 > 1, 1977, 1, 24.8124 > 1, 1978, 1, 23.0570 > 1, 1978, 0, 14.5627 > 1, 1979, 1, 21.2071 > 1, 1979, 0, 13.5277 > 2, 1975, 1, 62.4457 > 2, 1975, 0, 26.9745 > 2, 1976, 1, 67.3025 > 2, 1976, 0, 31.4600 > 2, 1977, 1, 53.0577 > 2, 1977, 0, 25.1941 > 2, 1978, 0, 23.3694 > 2, 1978, 1, 40.1452 > 2, 1979, 1, 44.5686 > 2, 1979, 0, 23.4042 > > ______________________________________________ > 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.