[R] Substituting the extracted coefficients into the formula, exctracted from the result of nls()

[Henrique Dallazuanna]

Try with predict:

plot(x, y)
lines(0:10, predict(yfit, list(x = 0:10)))

2009/10/9 Primoz PETERLIN <primozz.peterlin at gmail.com>:
> Dear all,
>
> Here I come with another stupid question.  Suppose I want to use nls()
> to fit a series of data (here modelled by generated points), then plot
> the points and the fitting curve. I figured out some way of doing it:
>
> x <- runif(1:20, 0, 10)
> y <- 0.1*x^2 - rep(3, length(x)) + rnorm(length(x), sd = 0.5)
>
> yfit <- nls(y ~ a*x^2 + b*x + c,
>            start = list(a = 1, b = 1, c = 1),
>            trace = TRUE)
>
> plot(x, y)
> curve(coef(yfit)[1]*x^2 + coef(yfit)[2]*x + coef(yfit)[3], 0, 10,
>      add = TRUE)
>
> However, this code is rather fortranesque, and most likely there
> exists a much more elegant way in R/S, something like abline() which
> exists for straight lines. Since both the formula and the coefficients
> are available as a result of nls() (here as formula(yfit) and
> coef(yfit)), I thought there ought to be a way something along the
> following lines:
>
> f <- substitute(formula(yfit), as.list(coef(yfit)))
> curve(f, ...)
>
> However, this snippet of code doesn't work. Am I thinking into the
> correct direction at all?
>
> Thanks in advance.
>
> All the best,
> Primož
>
> --
> Primož Peterlin,   Inštitut za biofiziko, Med. fakulteta, Univerza v Ljubljani
> Lipičeva 2, SI-1000 Ljubljana, Slovenija.        primoz.peterlin at mf.uni-lj.si
> Tel +386-1-5437612, fax +386-1-4315127,  http://biofiz.mf.uni-lj.si/~peterlin/
> F8021D69 OpenPGP fingerprint: CB 6F F1 EE D9 67 E0 2F  0B 59 AF 0D 79 56 19 0F
>
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-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O