Append multiple rows to an openCV matrix [duplicate] - c++

Question

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Add a row to a matrix in OpenCV
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Closed 5 years ago.
Can alyone tell me how to append a couple of rows (as a cv::Mat) at the end of an existing cv::Mat? since it is a lot of data, I don't want to go through the rows with a for-loop and add them one-by-one. So here is what I want to do:
cv::Mat existing; //This is a Matrix, say of size 700x16
cv::Mat appendNew; //This is the new Matrix with additional data, say of size 200x16.
existing.push_back(appendNew);
If I try to push back the smaller matrix, I get an error of non-matching sizes:
OpenCV Error: Sizes of input arguments do not match
(Pushed vector length is not equal to matrix row length)
So I guess .push_back() tries to append the whole matrix like a kind of new channel, which won't work because it is much smaller than the existing matrix. Does someone know if the appending of the rows at the end of the existing matrix is possible as a whole, not going through them with a for-loop?
It seems like an easy question to me, nevertheless I was not able to find a simple solution online... So thanks in advance!
Cheers:)

Answer 1

You can use cv::hconcat() to append rows, either on top or bottom of a given matrix as:
import cv2
import numpy as np
box = np.ones((50, 50, 3), dtype=np.uint8)
box[:] = np.array([0, 0, 255])
sample_row = np.ones((1, 50, 3), dtype=np.uint8)
sample_row[:] = np.array([255, 0, 0])
for i in xrange(5):
box = cv2.vconcat([box, sample_row])
===>
For visualization purposes I have created a RGB matrix with red color and tried to append Blue rows to the bottom, You may replace with original data, Just make sure that both the matrices to be concatenated have same number of columns and same data type. I have explicitly defined the dtype while creating matrices.