[R] stepAIC invalid scope argument

[John Wilkinson (pipex)]

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