[R] graphing repeated curves

[Jim Lemon]

Hi Richard,
This may be what you want:

data(mtcars)
m<-list()
for(i in 1:6) {
 rhterms<-paste(paste0("I(hp^",1:i,")"),sep="+")
 lmexp<-paste0("lm(mpg~",rhterms,",mtcars)")
 cat(lmexp,"\n")
 m[[i]]<-eval(parse(text=lmexp))
}
plot(mpg~hp,mtcars,type="n")
for(i in 1:6) abline(m[[i]],col=i)

Jim


On Thu, Aug 23, 2018 at 9:07 AM, Richard Sherman <rss.pdx using gmail.com> wrote:
> Hi all,
>
> I have a simple graphing question that is not really a graphing question, but a question about repeating a task.
>
> I’m fiddling with some of McElreath’s Statistical Rethinking, and there’s a graph illustrating extreme overfitting (a number of polynomial terms in x equal to the number of observations), a subject I know well having taught it to grad students for many years.
>
> The plot I want to reproduce has, in effect:
>
> m1 <- lm( y ~ x)
> m2 <- lm( y ~ x + x^2)
>
> …etc., through lm( y ~ x + x^2 + x^3 + x^4 + x^5 + x^6 ), followed by some plot() or lines() or ggplot2() call to render the data and fitted curves.
>
> Obviously I don’t want to run such regressions for any real purpose, but I think it might be useful to learn how to do such a thing in R without writing down each lm() call individually. It’s not obvious where I’d want to apply this, but I like learning how to repeat things in a compact way.
>
> So, something like:
>
> data( mtcars )
> d <- mtcars
> v <- c( 1 , 2 , 3 , 4 , 5 , 6  )
> m1 <- lm( mpg ~ hp  , data = d )
>
> and then somehow use for() with an index or some flavor of apply() with the vector v to repeat this process yielding
>
> m2 <- lm( mpg ~ hp + I( hp ^2 ) , data=d)
> m3 <- lm( mpg ~ hp + I( hp^2 ) + I(hp^3) , data=d )
>
> … and the rest through m6 <- lm( mpg ~ hp + I(hp^2) + I(hp^3) + I(hp^4) + I(hp^5) + I(hp^6) , data=d )
>
> But finding a way to index these values including not just each value but each value+1 , then value+1 and value+2, and so on escapes me. Obviously I don’t want to include index values below zero.
>
> ===
> Richard Sherman
> rss.pdx using gmail.com
>
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