[R] Extracting the names of coefficients of random effects

Brian Willis b.h.willis at bham.ac.uk
Sat Apr 19 17:51:19 CEST 2014

Hi All,
I need to be able to manipulate the names of the coefficients from

If there is any missing data when fitting a mixed model using lmer, no
estimate is returned for the associated level for that random effect. Thus
if the data input for regions had levels 
and there was missing data on Bradford then 
* ranef(model)*					gives 
Bolton:                               	          -0.0981763413
Cambridge		                                   0.0151102347
Durham						   0.1837142259

This becomes a problem if I want to use *predict( )* on new data where there
is no missing data on Bradford. In such an instance

	*predict (model, newdata = newInput) *	gives the following error message 

             ‘Error in (function (x, n)  : new levels detected in newdata’

I could get round this by checking the Region field of the new data
‘newInput’ against the names of the levels of the intercept coefficients
from* ranef().*
However, I’m not sure how to access these since if 
*x<- ranef(model)
x *
This gives the same output above, but

	*x[1,1]* only returns the numeric value  -0.0981763413

x is a dataframe with only one field (column) with numeric values and the
names of the levels are not present or identified. There must be a variable
which defines ‘Bolton’, Bradford’ etc since if I use the write.table
*write.table (x, file="/desktop/Dummy.csv", sep = ",",  col.names = NA, 
qmethod = "double")*
This outputs both the names (‘Bolton’, Bradford’..) and their corresponding
numeric values to a spreadsheet.

Does anyone know how to do this without resorting to outputting to a

Brian H Willis
Health and Population Sciences
University of Birmingham

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