How to efficiently retrieve a subset of cv :: Mat

Question

A common goal of machine learning is to have the first column of a data set representing the class to which the corresponding row for the data point belongs.

Basically, I have cv :: Mat, and I want to efficiently create a cv :: Mat containing this matrix with the first column removed. Is there a more efficient way to do this than iterate over columns and rows and add items one by one with mat.at<data_type>(row, col) = elem; ?

Answer 1

See Mat :: operator () from the OpenCV documentation.