grouping.levels: Returns the levels of a grouping factor in a mixed effects regression model
Description
Helper function returning all the levels of a grouping factor in a mixed effects regression model.
Usage
grouping.levels(model, group)
Arguments
model
Mixed effects model of class 'mer'
group
Grouping factor of 'model' of which the levels are returned
Value
Returns a character vector containing all the names / labels of levels of the grouping factor.
Details
Please note that at times different results may be obtained by using nesting.levels(), compared with deriving the levels of the grouping factor directly from the (original) data. This is because nesting.levels() only extracts the nesting levels that were de facto used in the model. Due to missing values, this may diverge from those present in the actual data.
# Penicillin data originates from the lme4 package. model <- lmer(diameter ~ (1|plate) + (1|sample), Penicillin)
grouping.levels(model, "plate")
grouping.levels(model, "sample")