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.
