[R] bug in nls?

From: Petr PIKAL <petr.pikal_at_precheza.cz>
Date: Thu, 26 Jun 2008 13:57:39 +0200


Dear all

Nobody responded to my previous post so far so I try with more offending subject.

I just encountered a strange problem with nls formula. I tried to use nls in cycle but I was not successful. I traced the problem to some parse command.

Here is an example

DF<-data.frame(x=1:10, y=3*(1:10)^.5+rnorm(10))

coef(lm(log(DF[,2])~log(DF[,1])))
 (Intercept) log(DF[, 1])
   0.7437320 0.6831726
# this works

coef(nls(y~a*x^b, data=DF, start=list(a=3, b=.7)))

        a b
2.6412881 0.5545907
# OK, this works too

coef(nls(DF[,2]~a*DF[,1]^b, data=DF, start=list(a=3, b=.7))) Error in parse(text = x) : unexpected end of input in "~ " coef(nls(DF[,2]~a*DF[,1]^b, start=list(a=3, b=.7))) Error in parse(text = x) : unexpected end of input in "~ " # but this does not

Browse[1]>
debug: mf$formula <- as.formula(paste("~", paste(varNames[varIndex],

    collapse = "+")), env = environment(formula)) Browse[1]>
Error in parse(text = x) : unexpected end of input in "~ "
>

Actually the problem is that with calling nls with DF[,n]~... varNames and varIndex is not correctly specified.

I am not sure if this behaviour is a bug or feature. If it is a feature, please help me how to call variables from data frame when using nls inside cycle

for (i in ....) result[i,] <- coef(nls( ...., ))

Thank you
Petr

> sessionInfo()

R version 2.8.0 Under development (unstable) (2008-05-18 r45723) i386-pc-mingw32

locale:

LC_COLLATE=Czech_Czech Republic.1250;LC_CTYPE=Czech_Czech 
Republic.1250;LC_MONETARY=Czech_Czech 
Republic.1250;LC_NUMERIC=C;LC_TIME=Czech_Czech Republic.1250

attached base packages:
[1] stats     grDevices datasets  utils     graphics  methods   base 

other attached packages:
[1] nlme_3.1-88 lattice_0.17-7 fun_0.1

loaded via a namespace (and not attached): [1] grid_2.8.0 tools_2.8.0

Petr Pikal
petr.pikal_at_precheza.cz
724008364, 581252140, 581252257



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