Thank you. Your suggestion is equivalent is the same as my second stepAIC command that failed in R-2.1.1. See Prof. Ripley's reply where he pointed out that this was due to using the name 'df' which clashes with built-in function with the same name from stats package. Regards, Adai
On Tue, 2005-08-16 at 15:52 +0100, John Wilkinson (pipex) wrote:
Adai, The following works.Perhaps you should define your 'upper' and 'lower' in the list as aov's, as you have done with your lo,hi and mid. John
stepAIC( mid, scope=list(upper = mid , lower = lo) )
Start: AIC= -594.66
y ~ x2 + x3
Df Sum of Sq RSS AIC
- x2 1 0.11 548.56 -596.45
- x3 1 0.95 549.40 -594.93
<none> 548.45 -594.66
Step: AIC= -596.45
y ~ x3
Adaikalavan Ramasamy wrote ---
I am trying to replicate the first example from stepAIC from the MASS
package with my own dataset but am running into error. If someone can
point where I have gone wrong, I would appreciate it very much.
Here is an example :
set.seed(1)
df <- data.frame( x1=rnorm(1000), x2=rnorm(1000), x3=rnorm(1000) )
df$y <- 0.5*df$x1 + rnorm(1000, mean=8, sd=0.5)
# pairs(df); head(df)
lo <- aov( y ~ 1, data=df )
hi <- aov( y ~ .^2, data=df )
mid <- aov( y ~ x2 + x3, data=df )
Running any of the following commands
stepAIC( mid, scope=list(upper = ~x1 + x2 + x3 , lower = ~1) )
stepAIC( mid, scope=list(upper = hi , lower = lo) )
addterm( mid, ~ x1 + x2 + x3 )
addterm( lo, hi )
gives the same error message :
Error in eval(expr, envir, enclos) : invalid second argumen