tom_pienkowski <tom.pienkowski <at> blueyonder.co.uk> writes: > I'm trying to use the 'by' function to extract the co-efficients from a > mixed model which is performed on multiple individuals. I basically have a > group of individuals and for each individual I want the co-efficient for > there change in 'pots_hauled' in response to a change in 'vpue' with my > random variable being 'ns_a_vpue'. > > The problem I am having is that the co-efficients for all my individuals are > returning as the same! So I'm not getting the individuals co-efficients, I'm > not even sure what it is returning. Here is a sample of my code: > > mod_1 <- lme(pots_hauled ~ rc_a_vpue ,(random = ~1 | a_vpue), data = data1) > > by(data1, id, summary) > > by(data1, list(pots_hauled=pots_hauled,id=id ), summary) > > by(data1, id, function(x) lme(pots_hauled ~ a_vpue ,(random = ~1 | > ns_a_vpue), data = data1))) > > lmid <- by(data1, id, function(x) lme(pots_hauled ~ a_vpue ,(random = ~1 | > ns_a_vpue), data = data1)) > > sapply(lmid, coef) >
I think your problem is that you're specifying "data=data1" in your function call, which means that by() doesn't get a chance to substitute the correct individual-specific data. I would suggest lmid <- by(data1, id, lme, fixed= pots_hauled ~ a_vpue , random = ~1 | ns_a_vpue) which should automatically insert the appropriate chunk of 'data1' as the data= argument in lme. I would further suggest that you probably want sapply(lmid,fixef) rather than sapply(lmid,coef) (which will return the coefficients for each random-effects level within individuals) I would furthermore suggest that you might want to (a) consider using a multilevel random-effects model where individuals were also a random effect (rather than testing each individual separately and (b) send followups to r-sig-mixed-mod...@r-project.org (the special interest group on mixed models) Ben Bolker ______________________________________________ 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.
