[R] Predicting from an nls model

From: Ranney, Steven <steven.ranney_at_montana.edu>
Date: Thu, 12 Jun 2008 06:42:20 -0600


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

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