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copied!<p>You can define you own iterator over the columns, so that you can use standard algorithms (like <code>for_each</code>, or <code>transform</code> as mentionned in another answer) to apply you function either to rows or columns of you array by just changing the iterators:</p> <pre><code>#include <iostream> #include <iterator> #include <vector> #include <algorithm> // Custom iterator to iterate over columns // to be adapted to the underlying storage class ColIterator : public std::iterator<std::forward_iterator_tag, double> { public: typedef std::vector<std::vector<double> > MDarray; ColIterator(MDarray & array, int i, int j) : array_(array), i_(i), j_(j) {} ColIterator(const ColIterator& it) : array_(it.array_), i_(it.i_), j_(it.j_) {} ColIterator& operator++() { ++i_; return *this; } ColIterator operator++(int) { ColIterator tmp(*this); operator++(); return tmp; } bool operator==(const ColIterator& rhs) { return &array_==&rhs.array_ && i_==rhs.i_ && j_==rhs.j_; } bool operator!=(const ColIterator& rhs) { return !operator==(rhs); } double& operator*() {return array_[i_][j_];} private: MDarray & array_; int i_; int j_; }; // a function void mult2 (double & x) { x *= 2; } int main () { typedef std::vector<double>::iterator RowIterator; int nRows = 5; int nCols = 5; ColIterator::MDarray array (nRows, std::vector<double>(nCols, 1)); // Apply function mult2 to column 3 int col = 3; ColIterator beginCol (array, 0, col); ColIterator endCol (array, nRows, col); std::for_each(beginCol, endCol, mult2); // Apply function mult2 to row 4 int row = 4; RowIterator beginRow (array[row].begin()); RowIterator endRow (array[row].end()); std::for_each(beginRow, endRow, mult2); // Check results for (int i=0 ; i<nRows ; ++i) { for (int j=0 ; j<nCols ; ++j) { std::cout << " " << array[i][j]; } std::cout << std::endl; } return 0; } </code></pre>

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