Implement evaluator for Select.

Eigen/src/Core/CoreEvaluators.h

@@ -576,6 +576,45 @@ struct evaluator_impl<Block<XprType, BlockRows, BlockCols, InnerPanel, /* HasDir
 };
 
 
+// -------------------- Select --------------------
+
+template<typename ConditionMatrixType, typename ThenMatrixType, typename ElseMatrixType>
+struct evaluator_impl<Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> >
+{
+  typedef Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> SelectType;
+
+  evaluator_impl(const SelectType& select) 
+    : m_conditionImpl(select.conditionMatrix()),
+      m_thenImpl(select.thenMatrix()),
+      m_elseImpl(select.elseMatrix())
+  { }
+ 
+  typedef typename SelectType::Index Index;
+  typedef typename SelectType::CoeffReturnType CoeffReturnType;
+
+  CoeffReturnType coeff(Index row, Index col) const
+  {
+    if (m_conditionImpl.coeff(row, col))
+      return m_thenImpl.coeff(row, col);
+    else
+      return m_elseImpl.coeff(row, col);
+  }
+
+  CoeffReturnType coeff(Index index) const
+  {
+    if (m_conditionImpl.coeff(index))
+      return m_thenImpl.coeff(index);
+    else
+      return m_elseImpl.coeff(index);
+  }
+ 
+protected:
+  typename evaluator<ConditionMatrixType>::type m_conditionImpl;
+  typename evaluator<ThenMatrixType>::type m_thenImpl;
+  typename evaluator<ElseMatrixType>::type m_elseImpl;
+};
+
+
 } // namespace internal
 
 #endif // EIGEN_COREEVALUATORS_H

Eigen/src/Core/Select.h

@@ -101,6 +101,21 @@ class Select : internal::no_assignment_operator,
         return m_else.coeff(i);
     }
 
+    const ConditionMatrixType& conditionMatrix() const
+    {
+      return m_condition;
+    }
+
+    const ThenMatrixType& thenMatrix() const
+    {
+      return m_then;
+    }
+
+    const ElseMatrixType& elseMatrix() const
+    {
+      return m_else;
+    }
+
   protected:
     const typename ConditionMatrixType::Nested m_condition;
     const typename ThenMatrixType::Nested m_then;

test/evaluators.cpp

@@ -164,4 +164,7 @@ void test_evaluators()
   matXcd_ref.real() = mat1;
   matXcd_ref.imag() = mat2;
   VERIFY_IS_APPROX(matXcd, matXcd_ref);
+
+  // test Select
+  VERIFY_IS_APPROX_EVALUATOR(aX, (aXsrc > 0).select(aXsrc, -aXsrc));
 }