R help - Apr 2009 - Plotting polynomial fit

Hi.

Is there an analog to abline() that can be used to plot a polynomial fit?

For example, I can draw the straight-line fit

    fit <- lm(y ~ x)

via

    abline(coef=fit$coef)

but I'm not sure how to draw the polynomial fit

    fit <- lm(y ~ poly(x,2))

I do see the function curve(), but not how to prepare an expr for 
curve() based on the coefficients returned by the polynomial fit.

Thanks for your help,

/Ronnen.

/P.S. E-mailed CCs of posted replies appreciated.

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On Apr 26, 2009, at 8:40 PM, Ronnen Levinson wrote:
> Hi.
>
> Is there an analog to abline() that can be used to plot a polynomial  
> fit?
>
> For example, I can draw the straight-line fit
>
>    fit <- lm(y ~ x)
>
> via
>
>    abline(coef=fit$coef)
>
> but I'm not sure how to draw the polynomial fit
>
>    fit <- lm(y ~ poly(x,2))
>
> I do see the function curve(), but not how to prepare an expr for
> curve() based on the coefficients returned by the polynomial fit.
>
> Thanks for your help,
Use instead the predict function. Something like:

lines(x=seq(min(x), max(x), length=100), y= predict( fit,  
newdata=  ....) #insert properly constructed dataframe



David Winsemius, MD
Heritage Laboratories
West Hartford, CT