Add a Select expression in the Array module which mimics a coeff-wise ?: operator.

Example:
  mat = (mat.cwise().abs().cwise() < Ones()).select(0,mat);
replaces all small values by 0. (the scalar version is "s = abs(s)<1 ? 0 : s")

Eigen/src/Array/Select.h

@@ -0,0 +1,153 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra. Eigen itself is part of the KDE project.
+//
+// Copyright (C) 2008 Gael Guennebaud <g.gael@free.fr>
+//
+// Eigen is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 3 of the License, or (at your option) any later version.
+//
+// Alternatively, you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of
+// the License, or (at your option) any later version.
+//
+// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License or the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License and a copy of the GNU General Public License along with
+// Eigen. If not, see <http://www.gnu.org/licenses/>.
+
+#ifndef EIGEN_SELECT_H
+#define EIGEN_SELECT_H
+
+/** \array_module \ingroup Array
+  *
+  * \class Select
+  *
+  * \brief Expression of a coefficient wise version of the C++ ternary operator ?:
+  *
+  * \param ConditionMatrixType the type of the \em condition expression which must be a boolean matrix
+  * \param ThenMatrixType the type of the \em then expression
+  * \param ElseMatrixType the type of the \em else expression
+  *
+  * This class represents an expression of a coefficient wise version of the C++ ternary operator ?:.
+  * It is the return type of MatrixBase::select() and most of the time this is the only way it is used.
+  *
+  * \sa MatrixBase::select(const MatrixBase<ThenDerived>&, const MatrixBase<ElseDerived>&) const
+  */
+
+template<typename ConditionMatrixType, typename ThenMatrixType, typename ElseMatrixType>
+struct ei_traits<Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> >
+{
+  typedef typename ei_traits<ThenMatrixType>::Scalar Scalar;
+  enum {
+    RowsAtCompileTime = ConditionMatrixType::RowsAtCompileTime,
+    ColsAtCompileTime = ConditionMatrixType::ColsAtCompileTime,
+    MaxRowsAtCompileTime = ConditionMatrixType::MaxRowsAtCompileTime,
+    MaxColsAtCompileTime = ConditionMatrixType::MaxColsAtCompileTime,
+    Flags = (unsigned int)ThenMatrixType::Flags & ElseMatrixType::Flags & HereditaryBits,
+    CoeffReadCost = ei_traits<ConditionMatrixType>::CoeffReadCost
+                  + EIGEN_ENUM_MAX(ei_traits<ThenMatrixType>::CoeffReadCost,
+                                   ei_traits<ElseMatrixType>::CoeffReadCost)
+  };
+};
+
+template<typename ConditionMatrixType, typename ThenMatrixType, typename ElseMatrixType>
+class Select : ei_no_assignment_operator,
+  public MatrixBase<Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> >
+{
+  public:
+
+    EIGEN_GENERIC_PUBLIC_INTERFACE(Select)
+
+    Select(const ConditionMatrixType& conditionMatrix,
+           const ThenMatrixType& thenMatrix,
+           const ElseMatrixType& elseMatrix)
+      : m_condition(conditionMatrix), m_then(thenMatrix), m_else(elseMatrix)
+    {
+      ei_assert(m_condition.rows() == m_then.rows() && m_condition.rows() == m_else.rows());
+      ei_assert(m_condition.cols() == m_then.cols() && m_condition.cols() == m_else.cols());
+    }
+
+    int rows() const { return m_condition.rows(); }
+    int cols() const { return m_condition.cols(); }
+
+    const Scalar coeff(int i, int j) const
+    {
+      if (m_condition.coeff(i,j))
+        return m_then.coeff(i,j);
+      else
+        return m_else.coeff(i,j);
+    }
+    
+    const Scalar coeff(int i) const
+    {
+      if (m_condition.coeff(i))
+        return m_then.coeff(i);
+      else
+        return m_else.coeff(i);
+    }
+
+  protected:
+    const typename ConditionMatrixType::Nested m_condition;
+    const typename ThenMatrixType::Nested m_then;
+    const typename ElseMatrixType::Nested m_else;
+};
+
+
+/** \array_module
+  *
+  * \returns a matrix where each coefficient (i,j) is equal to \a thenMatrix(i,j)
+  * if \c *this(i,j), and \a elseMatrix(i,j) otherwise.
+  *
+  * \sa class Select
+  */
+template<typename Derived>
+template<typename ThenDerived,typename ElseDerived>
+inline const Select<Derived,ThenDerived,ElseDerived>
+MatrixBase<Derived>::select(const MatrixBase<ThenDerived>& thenMatrix,
+                            const MatrixBase<ElseDerived>& elseMatrix) const
+{
+  return Select<Derived,ThenDerived,ElseDerived>(derived(), thenMatrix.derived(), elseMatrix.derived());
+}
+
+/** \array_module
+  *
+  * Version of MatrixBase::select(const MatrixBase&, const MatrixBase&) with
+  * the \em else expression being a scalar value.
+  *
+  * \sa MatrixBase::select(const MatrixBase<ThenDerived>&, const MatrixBase<ElseDerived>&) const, class Select
+  */
+template<typename Derived>
+template<typename ThenDerived>
+inline const Select<Derived,ThenDerived, NestByValue<typename ThenDerived::ConstantReturnType> >
+MatrixBase<Derived>::select(const MatrixBase<ThenDerived>& thenMatrix,
+                            typename ThenDerived::Scalar elseScalar) const
+{
+  return Select<Derived,ThenDerived,NestByValue<typename ThenDerived::ConstantReturnType> >(
+    derived(), thenMatrix.derived(), ThenDerived::Constant(rows(),cols(),elseScalar));
+}
+
+/** \array_module
+  *
+  * Version of MatrixBase::select(const MatrixBase&, const MatrixBase&) with
+  * the \em then expression being a scalar value.
+  *
+  * \sa MatrixBase::select(const MatrixBase<ThenDerived>&, const MatrixBase<ElseDerived>&) const, class Select
+  */
+template<typename Derived>
+template<typename ElseDerived>
+inline const Select<Derived, NestByValue<typename ElseDerived::ConstantReturnType>, ElseDerived >
+MatrixBase<Derived>::select(typename ElseDerived::Scalar thenScalar,
+                            const MatrixBase<ElseDerived>& elseMatrix) const
+{
+  return Select<Derived,NestByValue<typename ElseDerived::ConstantReturnType>,ElseDerived>(
+    derived(), ElseDerived::Constant(rows(),cols(),thenScalar), elseMatrix.derived());
+}
+
+#endif // EIGEN_SELECT_H