##Multilevel data frame of tree-ring widths:
data(Prings05,envir = environment())
## Names of variables in Prings05 data containing numeric classes:
cClass(Prings05, 'numeric') # 'x'
## Names of variables containing time units:
cClass(Prings05, 'integer') # 'year'
## Names of variables containing factors:
cClass(Prings05, 'factor') # 'sample', 'tree', 'plot'
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