Fix predict for drop_intercept models (#76)

* - fixed predict with drop_intercept model and categorical variabels bug
- add tests that used to fail but now pass

* reverted end of line changes

src/statsmodel.jl

@@ -90,12 +90,14 @@ StatsBase.r2(mm::DataFrameRegressionModel, variant::Symbol) = r2(mm.model, varia
 StatsBase.adjr2(mm::DataFrameRegressionModel, variant::Symbol) = adjr2(mm.model, variant)
 
 # Predict function that takes data frame as predictor instead of matrix
-function StatsBase.predict(mm::DataFrameRegressionModel, df::AbstractDataFrame; kwargs...)
+function StatsBase.predict(mm::DataFrameRegressionModel{T}, df::AbstractDataFrame; kwargs...) where T
     # copy terms, removing outcome if present (ModelFrame will complain if a
     # term is not found in the DataFrame and we don't want to remove elements with missing y)
     newTerms = dropresponse!(mm.mf.terms)
     # create new model frame/matrix
+    drop_intercept(T) && (newTerms.intercept = true)
     mf = ModelFrame(newTerms, df; contrasts = mm.mf.contrasts)
+    drop_intercept(T) && (mf.terms.intercept = false)
     newX = ModelMatrix(mf).m
     yp = predict(mm, newX; kwargs...)
     out = missings(eltype(yp), size(df, 1))

test/statsmodel.jl

@@ -39,6 +39,8 @@ StatsBase.coeftable(mod::DummyModNoIntercept) =
               ["'beta' value"],
               ["" for n in 1:size(mod.x,2)],
               0)
+StatsBase.predict(mod::DummyModNoIntercept) = mod.x * mod.beta
+StatsBase.predict(mod::DummyModNoIntercept, newX::Matrix) = newX * mod.beta
 
 ## Another dummy model type to test fall-through show method
 struct DummyModTwo <: RegressionModel
@@ -122,14 +124,20 @@ Base.show(io::IO, m::DummyModTwo) = println(io, m.msg)
     ct1 = coeftable(m1)
     ct2 = coeftable(m2)
     @test ct1.rownms == ct2.rownms == ["x1", "x2", "x1 & x2"]
+    @test predict(m1, d[2:4, :]) == predict(m1)[2:4]
+    @test predict(m2, d[2:4, :]) == predict(m2)[2:4]
 
     f1 = @formula(y ~ 1 + x1p)
     f2 = @formula(y ~ 0 + x1p)
     m1 = fit(DummyModNoIntercept, f1, d)
     m2 = fit(DummyModNoIntercept, f2, d)
+    m3 = fit(DummyModNoIntercept, f3, d, contrasts = Dict(:x1p => EffectsCoding()))
     ct1 = coeftable(m1)
     ct2 = coeftable(m2)
     @test ct1.rownms == ct2.rownms == ["x1p: 6", "x1p: 7", "x1p: 8"]
+    @test predict(m1, d[2:4, :]) == predict(m1)[2:4]
+    @test predict(m2, d[2:4, :]) == predict(m2)[2:4]
+    @test predict(m3, d[2:4, :]) == predict(m3)[2:4]
 
     m2 = fit(DummyModTwo, f, d)
     show(io, m2)