[R] plotting predicted values (lines) over data?

John Fox jfox at mcmaster.ca
Thu Jan 15 23:18:57 CET 2004

Dear Jeff,

I'm not sure that I follow entirely what you've done, but perhaps the 
following suggestions will help: (1) If the plotted curve isn't smooth 
because it's evaluated at too few x-values or at x-values that are too 
unevenly spaced, what about getting a sufficient number of predicted values 
[via predict()] that are evenly spaced along the range of ht -- i.e., not 
at the observations? (2) Rather than connecting the fitted values with line 
segments, you could use spline() to interpolate.

I hope that this helps,

At 11:23 AM 1/15/2004 -0800, Jeff D. Hamann wrote:
>I've been trying to plot the predicted values, as a line, over the data for
>a simple nonlinear fit with the following commands:
>plot( hg ~ ht )
>... define some function hg ~ ht + junk ...
>... blah, blah, obtain parameter estimates and predicted values, blah...
>... then...
>lines( sort( $predicted ) ~ sort( ht ) )
>which results in a line that isn't smooth (which I knew would happen). I've
>checked the FAQ,docs and archives and I'm not sure if there's function that
>will so what Heut et. al (2004) do with their plfit(). So, is there already
>an R function, or process to do this, or will I have to write one?

John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox

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