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how to assign all items in vector std::vector<std::vector<cv::Point> > test to 0?

Jul 6, 2022 at 12:46am
jNc (66)
how to assign all items in vector std::vector<std::vector<cv::Point> > test to 0?
Jul 6, 2022 at 1:16am
JLBorges (13770)
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std::vector<std::vector<cv::Point> > test ;
// ...
for( auto& pt : test ) pt = {} ;
Jul 6, 2022 at 1:21am
deleted account xyzzy (5768)
Has the 2D vector already been sized and populated? If so loop through each dimension and zero out the individual elements.

Here's some code to illustrate how to deal with a 2D vector as a whole.
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#include <iostream>
#include <vector>

template <typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& v);

template <typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<std::vector<T>>& v);

int main()
{
   const size_t row_size { 3 };
   const size_t col_size { 4 };

   // create a sized 2D vector filled with a set value for all the elements.
   // 50 in this case.
   std::vector<std::vector<int>> a2DVec(row_size, std::vector<int>(col_size, 50));

   for (const auto& row : a2DVec)
   {
      for (const auto& col : row)
      {
         std::cout << col << ' ';
      }
      std::cout << '\n';
   }
   std::cout << '\n';

   const int zero { };

   for (auto& row : a2DVec)
   {
      for (auto& col : row)
      {
         col = zero;
      }
   }

   /*for (const auto& row : a2DVec)
   {
      for (const auto& col : row)
      {
         std::cout << col << ' ';
      }
      std::cout << '\n';
   }*/

   // let's use a couple of templated std::ostream::operator<< overrides.
   // they make displaying a 1D and 2D vector as easy as plain old data
   // like an int or std::string
   std::cout << a2DVec;
}

template <typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& v)
{
   for (auto const& x : v)
   {
      os << x << ' ';
   }

   return os;
}

template <typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<std::vector<T>>& v)
{
   for (auto const& x : v)
   {
      os << x << '\n';
   }

   return os;
}
Edit & run on cpp.sh
50 50 50 50
50 50 50 50
50 50 50 50

0 0 0 0
0 0 0 0
0 0 0 0

Changing all the elements in an already created 2D vector is easy.

I don't know what cv::Point is, and honestly don't bother telling me. :)

Creating a sized 2D vector from scratch with a set cv::Point value as default shouldn't be that hard. Just create a temp copy of your cv:Point object initialized to zero and have that value as col value instead of 50 in my example.
Jul 6, 2022 at 9:27pm
jNc (66)

JLBorges (13438)
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std::vector<std::vector<cv::Point> > test ;
// ...
for( auto& pt : test ) pt = {} ;


Thank you!

Now I initialize matrix 100x10 with CV:Point like this:

std::vector<std::vector<cv::Point> > test
{
{{0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}} ,
{{0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}, {0 , 0} , {0 , 0} , {0 , 0}} ,

How should Initialize it right?
Jul 6, 2022 at 11:29pm
mbozzi (3943)
std::vector<std::vector<cv::Point>> test(100, {10, {0, 0}});
You would have found an answer more quickly by reading the documentation:
https://en.cppreference.com/w/cpp/container/vector/vector

Last edited on Jul 6, 2022 at 11:29pm
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