[R] How do I include a factor in a groupedData object? Meaning and use of inner and outer parameters

Sorkin, John jsorkin at som.umaryland.edu
Thu Mar 22 13:59:44 CET 2018

Windows 10 64-bit, R-Studio, R version 3.4.3

Several questions relating to groupedData:

(1) I am trying to create a groupedData object that can be used to run an analysis that I have been able to urn using lmer. When I include the interaction terms in the groupedData opbject I get an error message stating that + is not meaningful for factors. How do I include factors in my model? See code and error below.

(2) I have read the help file for groupedData multiple times. I am unable to understand the meaning or, or the use for the inner= and outer= parameters in the call to groupedData. Can someone either explain the meaning of these parameters or refer me to a source that give a clear explanation?

> fit0 <- lmer(THmean~INTRVNTN+factor(TimePtID)+INTRVNTN*factor(TimePtID)+(1|PatientID),data=smalldata)
> sdgd <- groupedData(THmean~INTRVNTN+TimePtID+INTRVNTN*TimePtID|PatientID,data=smalldata)
Warning messages:
1: In Ops.factor(INTRVNTN, TimePtID) : �+� not meaningful for factors
2: In Ops.factor(INTRVNTN, TimePtID) : �*� not meaningful for factors

Thank you,


John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
Baltimore VA Medical Center
10 North Greene Street
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)

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