[R] understanding I() in lmer formula

Don Cohen don-r-help at isis.cs3-inc.com
Tue Jun 13 20:25:54 CEST 2017


 Is there a difference between I(x*y) and I(y*x) ?
I have a call to lmer that results in this complaint:
  Error in is.alpha2.subordinate * ~z.min.co.res :  
  non-numeric argument to binary operator
when I change this line:
  I(is.alpha2.subordinate*z.min.co.res)+
to this:
  I(z.min.co.res*is.alpha2.subordinate)+
the complaint goes away.
I'd like to understand why.



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