[R] Linear Contrasts in GLM - Query

Hi, Is there a way I can specify linear contrasts in glm? I'm looking for something equivalent to SAS' contrast statement. I'd like to do the following, suppose I have a categorical input with 4 levels (a,b,c,d), I'd like to test something like: (i) a+b=c+d, (ii) a=b, (iii) a=b+d, etc... Thanks

Re: [R] Linear Contrasts in GLM - Query

: [R] Linear Contrasts in GLM - Query Hi, Is there a way I can specify linear contrasts in glm? I'm looking for something equivalent to SAS' contrast statement. I'd like to do the following, suppose I have a categorical input with 4 levels (a,b,c,d), I'd like to test somethin