Merging vector of vectors

Question

My class is

 class aMatrix { private: std::vector<std::vector<double> > mat; unsigned rows; unsigned cols; ...}

I want to merge two matrixes using method

aMatrix aMatrix::merge(const aMatrix& ob){ this->mat.reserve(this->mat.size()+ob.mat.size()); this->cols+=ob.cols; this->mat.insert(this->mat.end(), ob.mat.begin(),ob.mat.end()); return *this; }

but it doesnt work. Any ideas how to make it work?

edit: there's no error. it just adds column of ~0 and then values than differ from ob.mat.

edit:

aMatrix mat1(3,3); mat1(0, 0) = 1; mat1(0, 1) = 1; mat1(0, 2) = 1; mat1(1, 0) = 2; mat1(1, 1) = 3; mat1(1, 2) = 5; mat1(2, 0) = 11; mat1(2, 1) = 0; mat1(2, 2) = 5; aMatrix ones(3,3); ones(0,0)=1; ones(1,1)=1; ones(2,2)=1; mat1.merge(ones);

the result is:

1, 1, 1, 1.11319e-308, 2, 3, 2, 3, 5, 1.11318e-308, 11, 0, 11, 0, 5, 1.11317e-308, 1, 0,

edit: How to make it work in such notation?

// Parameter Constructor aMatrix::aMatrix(unsigned _rows, unsigned _cols, const double& _initial) { mat.resize(_rows); for (unsigned i = 0; i < mat.size(); i++) { mat[i].resize(_cols, _initial); } rows = _rows; cols = _cols; }

edit: OK, it works now. right code:

aMatrix& aMatrix::merge(const aMatrix& ob){ this->mat.reserve(this->mat.size()+ob.mat.size()); this->cols+=ob.cols; for (unsigned i = 0; i < this->mat.size(); i++) { this->mat[i].insert(this->mat[i].end(), ob.mat[i].begin(),ob.mat[i].end() ); } return *this; }

thanks :)

can you provide a minimum working code that reproduces the error? — coyotte508
– coyotte508, Commented Apr 18, 2015 at 18:05
Aside: You probably meant for the return value to be aMatrix&, not aMatrix. — user1084944
– user1084944, Commented Apr 18, 2015 at 19:17

Xiaotian Pei · Accepted Answer · 2015-04-18 18:16:25Z

1

You should do the merge row by row. What you are doing in your code is adding more rows to the original matrix. What you are intended to do is add more columns to the original matrix.

answered Apr 18, 2015 at 18:16

Xiaotian Pei

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2 Comments

coyotte508 Over a year ago

Ah, nice catch. And here I was wondering why my code was running fine: ideone.com/UFJlCa .

Xiaotian Pei Over a year ago

@coyotte508, your are using a column-major way, then it's fine.

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