Hello list
 
Does anybody know of any way to create an index of all the possible
combinations of variables (factors) in a data frame? ie for 3 factors A, B &
C we have 
 
A
B
C
AB
AC
BC
ABC
 
which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
 
I realise that a function like model.matrix does this, but how to get the
seqence of the index?
 
Any help would be greatly appreciated.
 
Regards
 
Alan Simpson
Roberts Research Group
 

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