R help - Aug 2006 - predict.lm within a function

Hi
I'm trying to wrap predict.lm within a function, but I'm having problems
passing arguments into it in this way.

Basically I want to create a lm object, then pass it into the predict.lm 
function and be able to tell predict.lm which variable I want to predict 
for, by passing the variable name as an argument of the wrapper 
function. This variable will always be a factor with 3 levels, so I want 
to predict the response within each of these levels evaluated at the 
mean value of all other variables in the model (as indicated below by 
replicating the means for the data 3 times in the data.frame part of 
predict.lm).

The simplest of all my attempts looks like this:

my.fun <- function(formula, mydata, predict_variable){
        my.lm <- lm(formula=formula, data=mydata)
        my.predict <- 
predict.lm(my.lm,(data.frame(predict_variable=y,rbind(mean(mydata, 
na.rm=T),mean(mydata, na.rm=T), mean(mydata,na.rm=T)), 
row.names=as.numeric(names(table(mydata$predict_variable))))))
        }

outside of the function, the following commands do exactly what I want:

my.lm <- lm(LDL ~ AGE + SEX + factor(SNP1_add), data=testdata)
predict.lm(my.lm,(data.frame(SNP1_add=y,rbind(mean(testdata, 
na.rm=T),mean(testdata, na.rm=T), mean(testdata,na.rm=T)), 
row.names=as.numeric(names(table(testdata$SNP1_add))))))

where SNP1_add is the variable to predict for, but when I run

my.fun(formula=LDL ~ AGE + SEX + factor(SNP1_add), mydata=testdata, 
predict_variable="SNP1_add")

I get: Error in sort(unique.default(x), na.last = TRUE) :
        'x' must be atomic

I figure I should be using eval() or substitute() somewhere to but none 
of my attempts have been successful. Any help would be appreciated.

-- 
Pamela A McCaskie
BSc(Mathematical Sciences)(Hons)

Laboratory for Genetic Epidemiology
Western Australian Institute for Medical Research
University of Western Australia
Ground Floor, B Block
Hospital Avenue, Nedlands
Western Australia  6009
AUSTRALIA
Email:        pmccask at cyllene.uwa.edu.au
Phone:        +61 (0)8 9346 1612
Mob:          +61 (0)417 926 607

This e-mail and all attachments contain information which is confidential and/or
subject to copyright. It may not be used or disclosed unless authorised by the
sender.

Dear All, Sorry for spamming you with something trivial. I would like to plot a
"stepwise increasing function" (if that makes sense? See crude ASCHII
art below). I think there is some clever paramter for solving the problem but I
just cannot find it.


        _______________|
        |
        |
________|
|
|
|


Thank you in advance!


Cheers, Patrik

see
plot(y~x,type="s")

?hagen Patrik wrote:
> Dear All, Sorry for spamming you with something trivial. I would like to
plot a "stepwise increasing function" (if that makes sense? See crude
ASCHII art below). I think there is some clever paramter for solving the problem
but I just cannot find it.
> 
> 
>         _______________|
>         |
>         |
> ________|
> |
> |
> |
> 
> 
> Thank you in advance!
> 
> 
> Cheers, Patrik
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

confidentiality notice:
The information contained in this e-mail is confidential and...{{dropped}}

--- ?hagen Patrik <Patrik.Ohagen at mpa.se> wrote:
> 
> Dear All, Sorry for spamming you with something
> trivial. I would like to plot a "stepwise increasing
> function" (if that makes sense? See crude ASCHII art
> below). I think there is some clever paramter for
> solving the problem but I just cannot find it.
> 
> 
>         _______________|
>         |
>         |
> ________|
> |
> |
> |
> 
methods(plot)
?plot.stepfun

This looks like what you want