[FIXED] c++ implement of array broadcast

Issue

In python language, we can use A[A!=0]=-10 to trans all the non-zero value in A to -10. How can I implement this function in C++ language or is here any similar function in 3rd party?

#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <iostream>

using namespace std;
using namespace cv;

int main()
{
    Mat A(3, 3, CV_16SC1);
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            A.at<short>(i, j) = i + j;
        }
    }
    for (auto& value : A) if (value != 2) value = -10;
}

Solution

Range-based for loops will not work since the cv::Mat::begin() is a member function template. You'll have to use begin<mat_type>() and end<mat_type>().

Example:

#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>

#include <algorithm>
#include <iostream>
#include <iterator>

int main() {
    cv::Mat A(3, 3, CV_16SC1);

    using mtype = short;                              // convenience typedef

    for(int i = 0; i < 3; i++) {
        for(int j = 0; j < 3; j++) {
            A.at<mtype>(i, j) = i + j;                // using mtype
        }
    }

    // using mtype:
    for(auto it = A.begin<mtype>(); it != A.end<mtype>(); ++it) {
        if(*it != 2) *it = -10;
    }

    // print result:
    std::copy(A.begin<mtype>(), A.end<mtype>(),
              std::ostream_iterator<mtype>(std::cout, "\n"));
}

Or using the std::replace_if algorithm to replace all non 2's with -10:

    std::replace_if(A.begin<mtype>(), A.end<mtype>(),  // using mtype
        [](auto& value) { return value != 2; }, -10);

Output:

-10
-10
2
-10
2
-10
2
-10
-10

Answered By - Ted Lyngmo