[R] Calling update on an lm-object inside a function

[ONKELINX, Thierry]

Dear Soren,

I would try adding the new variable to the dataset and use the data = argument of lm

foo <- function(mod, data){
   data$y3 <- c(1,3,3,4,6)
   update(mod, y3 ~ ., data = data)
}
x <- 1:5
y <- c(1,2,3,3,6)
dataset <- data.frame(x = x, y = y)
mm <- lm(y~x, data = dataset)
foo(mm, dataset)

Best regards,

Thierry

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx op inbo.be
www.inbo.be

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-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org] Namens Søren Højsgaard
Verzonden: zondag 22 januari 2012 15:06
Aan: r-help op r-project.org
Onderwerp: [R] Calling update on an lm-object inside a function

Dear all,
I want to update an lm (or glm) object by changing the response variable and I want to do so inside a function. Doing the update outside of a function is straight forward:
 
 x <- 1:5
 y <- c(1,2,3,3,6)
 mm <- lm(y~x)
 y2 <- c(1,3,3,4,6)
 mm2<- update(mm, y2 ~ .)
 
But I want to make the update inside a function (where the new response variable is declared inside the function). If I do 
 
 foo <- function(mod){
   y3 <- c(1,3,3,4,6)
   update(mod, y3 ~ .)
 }
Then I get
 foo(mm)

Error in eval(expr, envir, enclos) : object 'y3' not found (because y3 is not known in the global environment - I suppose). To fix this I do
  
 foo2 <- function(mod){
   y3 <- c(1,3,3,4,6)
   mod2 <- eval(getCall(mod))
   update(mod2, y3 ~ .)
 }
 foo2(mm)

Call:
lm(formula = y3 ~ x)

Coefficients:
(Intercept)            x  
        0.1          1.1  

Question: Is this the "appropriate" way of making such a model "available" for an update inside a function, or is there a better way? I guess so - because:
If I change the model formula of my model and then invoke foo2 I get

mm3 <- update(mm,.~.-x)
> foo2(mm3)
Error in eval(expr, envir, enclos) : object 'y3' not found

This puzzles me. Question: can anyone help me clarify why this happens and what I can do to fix it.

Thanks in advance
Søren

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