Can I create a vector[][] from a vector[]

[tonnot]

I have a unidimensional vector with 10 rows of data
I'd like to fill my bidimensional vector[][] with the unidimensional vecto.
Using the example, I will have a vector[10][1].
I dont want to fill the data using a loop
Any idea ? Is there some method to construc the new vector directly from the unidimensional initial vector ?
Thanks

[jeffbmartinez]

If you don't want to *use* a loop, I'm not sure. But if you simply don't want to type the loop, you can do the following:

int const rows = 10;
int const columns = 10;

int uni[rows * columns];
int bi[rows][columns];

memcpy(bi, uni, sizeof(uni));

I'm guessing memcpy uses some kind of loop to do it's job internally.

Edit: An alternative that does not use a loop at all

Depending on what you're actually trying to do, you could avoid copying altogether and use a pointer to the unidimensional data to dereference as a bidimensional:

int TreatAs2D(int const *const uni, int const num_columns, int const column, int const row) {
    assert(row * column < sizeof(uni) / sizeof(uni[0])); // Don't go past your bounds
    return *(uni + (row * num_columns + column));
}

Now, instead of bi[1][2], you say TreatAs2D(uni, 10, 1, 2)

The second parameter is what tells TreatAs2D how many columns wide to treat your new "2D" array.

[tonnot]

Thanks, I'm going to try it.

[Osmar]

Let me see if I got it right!

The vector container has a ctor that allow you to fill elements in the vector like;

// all the includes and stuff...
vector<double> my_vec(10, .5);

Right there is a vector of ten doubles filled with value .5 (0.5) each. Now for what I understand you want to fill a matrix of 10 elements initilized with another vector, say, our 'my_vec' in this example. If so, it could be done like this:

typedef vector<vector<double>> Matrix;
Matrix mat(10, my_vec); // here is ur matrix filled with my_vec, without looping.
typedef Matrix::size_type index;

//Now to inspect the matrix you do need some looping
for(index i(0); i < mat.size(); ++i)
{
		for(index j(0); j < mat[0].size(); ++j)
			cout << mat[i][j] << ' '; // Note you use [][] sintax!
		endl(cout);
}

I'd prefer to wrap all that in a class of course, like this is horrible code but helps ilustrating...
Hope it helps!