Somewhat coincidentally this will work if you don't supply 'data=Data'.
On Thu, 31 Jul 2008, Prof Brian Ripley wrote:
On Thu, 31 Jul 2008, Lisa Readdy wrote:The following warning message occurs when running the nls on some data: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Warning message: In is.na(wts) : is.na() applied to non-(list or vector) of type 'NULL' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ and I would like to know what is causing it and how I can fix it. As an example, the following, from Venables and Ripley, which does not produce the warning message and then on the data which does procude the warning message. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ##Venables and rippley library(MASS) data(wtloss) wtloss.st = c(b0=90, b1=95, th=120) n1<-length(wtloss) Weight=c(1,rep(0.1,n1-1))wtloss.fm = nls(Weight ~ b0 + b1*2^(-Days/th), data=wtloss, start=wtloss.st,trace=T, weights=Weight )I am not sure what you think that does. It uses the Weight column of the data frame as the weights, which is not what you seem to have intended.wtloss.fm ##My data y<-c(73,73,70,74,75,115,105,107,124,107,116,125,102,144,178,149,177,124,157,128, 169,165,186,152,181,139,173,151,138,181,152,188,173,196,180,171,188,174,198,172, 176,162,188,182,182,141,191,190,159,170,163,197) x<-c(1,1,1,1,1,2,2,3,3,3,3,3,3,4,4,4,5,5,5,5,6,6,6,6,6,6,7,7,7,7,7,7,7,7,7,8,8,8, 8,8,8,8,8,8,8,9,9,9,9,9,11,12) Data<-data.frame(cbind(y,x)) n2<-length(x) weight<-c(1,rep(0.1,n2-1)) Ta<-min(Data$x) Tb<-max(Data$x) G.st<-c(k=0.005, g1=50,g2=550) #no weights growthFit<-nls(y~((g1)*exp((log(g2/g1))*(1-exp(-k*(x-Ta))) /(1-exp(-k*(Tb-Ta))))), data=Data, start=G.st, trace=T) #with weights growthFit.wts<-nls(y~((g1)*exp((log(g2/g1))*(1-exp(-k*(x-Ta))) /(1-exp(-k*(Tb-Ta))))), data=Data, start=G.st, trace=T, weights=weight)The difference here is that you don't have all your variables of the same length:Browse[1]> print(n) y x Ta Tb 52 52 1 1and the variable-finding mechanism is not set up to find weights in that case. That's a bug, but you can avoid it by substituting the scalars (e.g. using substitute()).-- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ 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.
-- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ 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.
