将向量推入向量

Question

I have a 2d vector

typedef vector <double> record_t;
typedef vector <record_t> data_t;
data_t data;

So my 2d vector is data here. It has elements like say,

1 1 1 1 1
2 2 2 2 2
3 3 3 3 3
4 4 4 4 4
5 5 5 5 5

Now I want to insert these elements into another 2d vector

 std::vector< vector<double> > window;

So what I did was to create an iterator for traversing through the rows of data and pushing it into window like

std::vector< std::vector<double> >::iterator data_it;

    for (data_it = data.begin() ; data_it != data.end() ; ++data_it){
      window.push_back ( *data_it );
      // Do something else
      }

Can anybody tell me where I'm wrong or suggest a way to do this ? BTW I want to push it just element by element because I want to be able to do something else inside the loop too. ie I want to check for a condition and increment the value of the iterator inside. for example, if a condition satisfies then I'll do data_it+=3 or something like that inside the loop.

Thanks

PS I asked this question last night and didn't get any response and that's why I'm posting it again.

Answer 1

If what you need is:

to check for a condition and increment the value of the iterator inside. for example, if a condition satisfies then I'll do it+=3 or something like that inside the loop.

Then using a while loop instead of a for migth help:

std::vector< std::vector<double> >::iterator data_it = data.begin();

while (data_it != data.end()) {
  window.push_back ( *data_it );
  if (SatisfiesCondition(*data_it)) {
    data_it += 3;
  }
  else {
    ++data_it;
  }
}

Answer 2

Your code currently copies the data row-by-row, not element-by-element.

For element-wise copying of a 2D array, you need a nested loop, as @AmbiguousX already mentioned. If you start with an empty 2D array window , the code should look like this:

for (std::vector< record_t >::iterator i = data.begin(); i != data.end(); i++)
{
  std::vector<double> row;
  for (std::vector<double>::iterator j = i->begin(); j != i->end(); j++)
  {
    row.push_back(*j);
    // do something else with *j
  }
  window.push_back(row);
}