please help by filling 2Dvector

Oct 29, 2012 at 1:45pm
noktalivirgul (53)
Hi;

I want to fill a 2D vector by some floats. can i use list.push_back again? How?for example I want to send 4.5 to the ithrow and jth column.
Last edited on Oct 29, 2012 at 2:28pm
Oct 29, 2012 at 3:34pm
SuperSonic (72)
If you want to push back something to the ith row then use this:
my_vector[i].push_back(4.5);

However, if you just want to assign 4.5 to the ith row and jth column, then do this:
my_vector[i][j] = 4.5;
Oct 29, 2012 at 3:52pm
noktalivirgul (53)
How do i define my vector if i use it in this way?? 1D or 2D?

my_vector[i].push_back(4.5);
does this line show in which column 4.5 is??
Oct 29, 2012 at 5:46pm
Stewbond (2827)
lets say you want a matrix like this: 
0 1 2
3 4 5
6 7 8


Just construct your rows, one at a time, then push them into the 2D vector like so:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
 
#include <vector>
#include <iostream>

int main()
{
    typedef std::vector<int> Row;
    std::vector<Row> my_vector;

    for (int row = 0; row < 3; ++row)
    {
        Row my_row;

        for (int col = 0; col < 3; ++col)
            my_row.push_back( row*3 + col );

        my_vector.push_back(my_row);
    }

    for (int row = 0; row < 3; ++row)
    {
        for (int col = 0; col < 3; ++col)
            std::cout << my_vector[row][col] << ' ';
        std::cout << std::endl;
    }
}
 
0 1 2 
3 4 5
6 7 8
Edit & run on cpp.sh


I like to use the Typedef when doing this because it makes it very clear that we have a vector of rows. std::vector< std::vector<int> > is too verbose for me.
Last edited on Oct 29, 2012 at 5:49pm
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