[R] Help with tryCatch with a for loop

[Spencer S]

Hello all,

I'm a beginner in R working on a script that will produce a set of models
(linear, polynomial and logistic) for each location in a dataset.  However,
the self-starting logistic model often fails - if this happens I would like
to just skip to the next iteration of the loop using tryCatch.  

I've looked at a few examples and read the help file, but didn't understand
tryCatch in the context of my script.  Any help or suggestions (even telling
me where to insert the tryCatch command) would be much appreciated!!

Below is the script I am currently working on:

data<-read.csv(file.choose(),sep=",",header=T)
#File name is cbc.subset

data$location.code = as.character(data$location.code)

locs = unique(location.code)

pdf("mygraphs.pdf",height=8, width=10)
par(mfrow=c(3,4))

for(s in 1:length(locs)){
  #To plot data from a particular stateroute:
  sub.ECDO<-data[data$location.code == locs[s],]
  plot(abund~year, data=sub.ECDO, main=locs[s])

  #To plot the linear model for the specified location:
  lmodel<-lm(abund~year, data=sub.ECDO)
  abline(lmodel$coefficients[1],lmodel$coefficients[2],lty=2)
 
  #To plot the polynomial model for the specified location:
  polymodel<-lm(abund~year+I(year^2), data=sub.ECDO)
  xv<-seq(min(sub.ECDO$year),max(sub.ECDO$year),0.1)
  yv<-predict(polymodel,list(year=xv))
  lines(xv,yv)

  #To plot the logistic model
  #####tryCatch
  logis<-nls(abund~SSlogis(year,a,b,c),data=sub.ECDO)
  yv<-predict(logis,list(year=xv))
  lines(xv,yv)

  #To find which model is the best fit:
  if ("logis" %in% ls()) {
    AIC.results = AIC(lmodel,polymodel,logis)
  } else {
    AIC.results = AIC(lmodel,polymodel)
  }
  
  #Add text to plot
  text(min(sub.ECDO$year)+2,0.9*max(sub.ECDO$abund),paste("linear =
",AIC.results[1,2],"\npolynomial = ",AIC.results[2,2],"\nlogistic =
",AIC.results[3,2],sep=""))
  
  rm(logis)
  rm(polymodel)
  rm(lmodel)
  
}

dev.off()

Thank you!

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