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src/statsmodel.jl

@@ -111,27 +111,48 @@ formula(m::TableRegressionModel) = m.mf.f
 
 Return the names of terms used in the formula of `model`.
 
-For regression models with only continuous predictors, this is the same as
+This is a convenience method for `termnames(formula(model))`.
+
+For `RegressionModel`s with only continuous predictors, this is the same as
 `(responsename(model), coefnames(model))`.
 
 For models with categorical predictors, the returned names reflect
 the variable name and not the coefficients resulting from
 the choice of contrast coding.
+"""
+termnames(model::StatisticalModel) = termnames(formula(model))
+"""
+    termnames(t::FormulaTerm)
+
+Return a two-tuple of `termnames` applied to the left and
+right hand sides of the formula.
+ 
+Note that until `apply_schema` has been called, literal `1` in formulae
+is interpreted as `ConstantTerm(1)` and will thus appear as `"1"` in the 
+returned term names.
 
 ```jldoctest
 julia> termnames(@formula(y ~ 1 + x * y + (1+x|g)))
 ("y", ["1", "x", "y", "x & y", "(1 + x) | g"])
 ```
+
+Similarly, formulae with an implicit intercept will not have a `"1"`
+in their term names, because the implicit intercept does not exist until 
+`apply_schema` is called (and may not exist for certain model contexts).
+
+```jldoctest
+julia> termnames(@formula(y ~ x * y + (1+x|g)))
+("y", ["x", "y", "x & y", "(1 + x) | g"])
+```
 """
-termnames(model::StatisticalModel) = termnames(formula(model))
+termnames(t::FormulaTerm) = (termnames(t.lhs), termnames(t.rhs))
 
 """
     termnames(term::AbstractTerm)
 
 Return the name(s) of column(s) generated by a term.  Return value is either a
 `String` or an iterable of `String`s.
 """
-termnames(t::FormulaTerm) = (termnames(t.lhs), termnames(t.rhs))
 termnames(::InterceptTerm{H}) where {H} = H ? "(Intercept)" : nothing
 termnames(t::ContinuousTerm) = string(t.sym)
 termnames(t::CategoricalTerm) = string(t.sym)