add hasintercept

src/regressionmodel.jl

@@ -40,6 +40,17 @@ Return the model matrix (a.k.a. the design matrix).
 """
 function modelmatrix end
 
+"""
+    hasintercept(model::RegressionModel)
+
+Indicate whether the model has an intercept.
+"""
+function hasintercept(model::RegressionModel)
+    X = modelmatrix(model)
+    any(i -> all(==(1), view(X , :, i)), 1:size(X, 2))
+end
+
+
 """
     crossmodelmatrix(model::RegressionModel)
 

test/regressionmodel.jl

@@ -1,7 +1,7 @@
 module TestRegressionModel
 
 using Test, LinearAlgebra, StatsAPI
-using StatsAPI: RegressionModel, crossmodelmatrix
+using StatsAPI: RegressionModel, hasintercept, crossmodelmatrix
 
 struct MyRegressionModel <: RegressionModel
 end
@@ -10,9 +10,10 @@ StatsAPI.modelmatrix(::MyRegressionModel) = [1 2; 3 4]
 
 @testset "TestRegressionModel" begin
     m = MyRegressionModel()
-
+
+    @test !hasintercept(m) 
     @test crossmodelmatrix(m) == [10 14; 14 20]
     @test crossmodelmatrix(m) isa Symmetric
 end
 
-end # module TestRegressionModel
+end # module TestRegressionModel