Suppose I have a formula
mfTest = (y ~ a + b + c + d1 + d2 + d3);
When I update the formula
mfTest2nd = update(mfTest, .~.^2);
I get all the combinations a:b, a:c, etc. But I don't want the d1:d2, d2:d3,
etc. interactions. I've tried
mfTest2nd = update(fmTest, .~.^2 - (d1+d2+d3)^2);
But that removes the 1st order variables as well. Is there a way to remove
(with minimal typing) the d_i:d_j interactions only? Thanks.
--Brett
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