[R] Error when using step

[Dieter Menne]

Chris Friedl <cfriedalek <at> gmail.com> writes:

> I have two questions about the built-in function step. Ultimately I want to
> apply a lm fitting and subsequent step procedure to thousands of data sets
> groups by a factor defined as a unique ID.
> 
> Q1. The code below creates a data.frame comprising three marginally noisy
> surfaces. The code below fails when I use step in a function but summary
> seems to show the model fits are legitimate. Any ideas on what I'm doing
> wrong?

... Well designed example code omitted
 
> function(x){lm(model, data = x)})
> lapply(fits, function(x){summary(x)})
> 
> # FAIL
> lapply(fits, function(x){step(x)})
....
> Error in as.data.frame.default(data) : 
>   cannot coerce class "lm" into a data.frame

Looks like an environment problem. I could not find a workaround quickly,
but you might have a look at 

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/16599.html

We call it "Ripley's Game" here, because variants of it can help you quite often.

Dieter