R help - Aug 2010 - "glmulti": defining which intractions between variables are to be included

Hello,

I'm using the "glmulti" package to run models of all the possible
combinations of my variables. However, I am only interested in a few
interactions between my variables.

I have tried the equivalent of:

mod1<-lm(y~a+b+c+a:b)
glmulti(mod1, level=1)

mod2<-lm(y~a+b+c+a:b)
glmulti(mod2, level=2)

and 

glmulti("y", c("a", "b", "c"),
exclude=c("a:c", "b:c" ), data=mydata)

where "mydata" is an object reading a text file.

However, the first code only gives me combinations of main effects (without
interactions), the second code doesn't allow me to exclude the a:c and b:c
interactions, and the third code doesn't allow me to define my variables as
factors becuase it uses character strings (and therefore runs a lot more models
than necessary).

Is there a way to use the third code, but tell R that some of the character
strings are factors?

Otherwise, since there are a lot more incteractions that I do not wish to test
than interactions that I do wish to test, is there an alternative by which
instead of having to exclude the interactions that I do not wish to test, I can
simply run models with the interaction terms that I include in my lm fromula?

Thank you in advance for your time,

Agnese

Hello,

I'm using the "glmulti" package to run models of all the possible
combinations of my variables. However, I am only interested in a few
interactions between my variables.

I have tried the equivalent of:

mod1<-lm(y~a+b+c+a:b)
glmulti(mod1, level=1)

mod2<-lm(y~a+b+c+a:b)
glmulti(mod2, level=2)

and

glmulti("y", c("a", "b", "c"),
exclude=c("a:c", "b:c" ), data=mydata)

where "mydata" is an object reading a text file.

However, the first code only gives me combinations of main effects (without
interactions), the second code doesn't allow me to exclude the a:c and b:c
interactions, and the third code doesn't allow me to define my variables as
factors becuase it uses character strings (and therefore runs a lot more models
than necessary).

Is there a way to use the third code, but tell R that some of the character
strings are factors?

Otherwise, since there are a lot more incteractions that I do not wish to test
than interactions that I do wish to test, is there an alternative by which
instead of having to exclude the interactions that I do not wish to test, I can
simply run models with only the interaction terms that I include in my lm
fromula?

Thank you in advance for your time,

Agnese