R help - Jun 2008 - Predicting from an nls model

I keep running up against the same error when I try to plot a line from a nls
model.  The data is fisheries length/weight data.  Code follows:

require(graphics)
pow = nls(Weight~alpha*Length^beta, data=wae,
      start=list(alpha=0.0000001, beta=3.0), trace=TRUE)
predict(pow)
plot(Weight~Length, data = wae, pch=19,
     xlab="Length (mm)", ylab="Weight (g)",
     xlim = c(150,1000), ylim = c(0, 10050))
mod = seq(150, 1000)
lines(mod, predict(pow, list(Weight = mod)))

The error I get after I submit the final line is:

Error in xy.coords(x, y) : 'x' and 'y' lengths differ

Like my last post, I'm certain there's something simple I'm
overlooking.  I've been able to get this to work on other data sets, but
_how_ I've been able to get this to work, I'm unsure.

Thanks for your help, 

SR

Steven H. Ranney
Graduate Research Assistant (Ph.D)
USGS Montana Cooperative Fishery Research Unit
Montana State University
PO Box 173460
Bozeman, MT 59717-3460

phone: (406) 994-6643
fax:   (406) 994-7479


	[[alternative HTML version deleted]]

Ranney, Steven <steven.ranney <at> montana.edu> writes:
                                                 
> plot(Weight~Length, data = wae, pch=19,
>      xlab="Length (mm)", ylab="Weight (g)",
>      xlim = c(150,1000), ylim = c(0, 10050))
          
> mod = seq(150, 1000)
          
> lines(mod, predict(pow, list(Weight = mod)))
> 
> The error I get after I submit the final line is:
> 
> Error in xy.coords(x, y) : 'x' and 'y' lengths differ
   Don't you need to specify Length (predictor
variable) rather than Weight (response variable)
to predict() in this case?

  Ben Bolker

To predict from Weight~alpha*Length^beta you need to specify Length, not 
Weight.  It is most likely finding Length from your workspace.

On Thu, 12 Jun 2008, Ranney, Steven wrote:
> I keep running up against the same error when I try to plot a line from a
nls model.  The data is fisheries length/weight data.  Code follows:
>
> require(graphics)
> pow = nls(Weight~alpha*Length^beta, data=wae,
>      start=list(alpha=0.0000001, beta=3.0), trace=TRUE)
> predict(pow)
> plot(Weight~Length, data = wae, pch=19,
>     xlab="Length (mm)", ylab="Weight (g)",
>     xlim = c(150,1000), ylim = c(0, 10050))
> mod = seq(150, 1000)
> lines(mod, predict(pow, list(Weight = mod)))
>
> The error I get after I submit the final line is:
>
> Error in xy.coords(x, y) : 'x' and 'y' lengths differ
>
> Like my last post, I'm certain there's something simple I'm
overlooking.  I've been able to get this to work on other data sets, but
_how_ I've been able to get this to work, I'm unsure.
>
> Thanks for your help,
>
> SR
>
> Steven H. Ranney
> Graduate Research Assistant (Ph.D)
> USGS Montana Cooperative Fishery Research Unit
> Montana State University
> PO Box 173460
> Bozeman, MT 59717-3460
>
> phone: (406) 994-6643
> fax:   (406) 994-7479
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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,                  ripley at stats.ox.ac.uk
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