Sorting cv::Mat in OpenCv

Question

Is there an equivalent function in OpenCV similar to [srtd,srtdinds] = sort(dst,'ascend'); in Matlab? I have tried cv::sortIdx(source, dst, cv::SORT_ASCENDING); but it doesn't work. My source Mat contains a single column.

Answer 1

From the documentation of cv::sortIdx():

Instead of reordering the elements themselves, it stores the indices of sorted elements in the output array.

This means that you will need to call cv::sort() to sort the elements themselves after calling cv::sortIdx() to replicate the behavior of Matlab's sort() function:

cv::Mat source = cv::Mat::eye(3,3,CV_32F), dst;
cv::sortIdx(source, dst, CV_SORT_EVERY_ROW + CV_SORT_ASCENDING);
cv::sort(source, source, CV_SORT_EVERY_ROW + CV_SORT_ASCENDING);

Now dst contains the permuted indices, and source contains the sorted data itself.