Estimating Weibull density parameters (error: “…initial value in 'vmmin' is not finite”)

Question

I am trying to estimate the shape and scale of a data set.
I used two different ways and for both I got an error message:

First, I tried by moments using the survey package:

survreg(Surv(all.ws)~1, dist="weibull")

I got the error message:

invalid survival times for this distribution

Second, I tried using fitdistr() function:

fitdistr(all.ws, densfun=dweibull, start=list(scale=1, shape=2))    

I got an error message:

Error in optim(x=c(2.2, 2.1,1.9....:
initial value in 'vmmin' is not finite

What is wrong with what I am doing?

Answer 1

A google search "fitdistr Weibull Error" shows this exact question was discussed a year ago on the R-help mailing list: http://r.789695.n4.nabble.com/Problems-with-fitdistr-td1334772.html

Some points from that link:

• zeros in your data will cause problems

• use pelwei() function from package lmom

Answer 2

I had a similar problem when using fitdistr() with a Beta distribution. In that case both ones and zeros in the data produced this error.

Additionally I found that when the limit argument is used in the fitdistr() call, a different error is produced: eg (where x is a vector of samples containing a 1.0 or 0):

fitdistr(x, "beta", list(shape1 = 1, shape2 = 0.2),lower=0.001)

   `Error in stats::optim: L-BFGS-B needs finite values of 'fn'`