Need a faster way to convert a cv::Mat into 1 dimensional vector form

Question

I have a for loop the takes an OpenCV Mat object of n x n dimensions, and returns a Mat object of n^2 x 1 dimensions. It works, but when I time the method it takes between 1 and 2 milliseconds. Since I am calling this method 3 or 4 million times its taking my program about an hour to run. A research paper I'm referencing suggests the author was able to produce a program with the same function that ran in only a few minutes, without running any threads in parallel. After timing each section of code, the only portion taking >1 ms is the following method.

static Mat mat2vec(Mat mat)
{

Mat toReturn = Mat(mat.rows*mat.cols, 1, mat.type());
float* matPt;
float* retPt;
for (int i = 0; i < mat.rows; i++) //rows
    {
        matPt = mat.ptr<float>(i);
        for (int j = 0; j < mat.row(i).cols; j++) //col
        {
            retPt = toReturn.ptr<float>(i*mat.cols + j);
            retPt[0] = matPt[j];
        }
    }
return toReturn;
}

Is there any way that I can increase the speed at which this method converts an n x n matrix into an n^2 x 1 matrix (or cv::Mat representing a vector)?

that solved most of the problem @berak, its running a lot faster now. however in some cases like below, the mat is not continuous. Any idea of how I can get an ROI in a continuous mat?

my method not looks like this:

static Mat mat2vec(Mat mat)
{
if ( ! mat.isContinuous() )
{ 
    mat = mat.clone();
}
return mat.reshape(1,2500);
}

Problems occur at:

Mat patch = Mat(inputSource, Rect((inputPoint.x - (patchSize / 2)), (inputPoint.y -        (patchSize / 2)), patchSize, patchSize));
Mat puVec = mat2vec(patch);

Answer 1

assuming that the data in your Mat is continuous, Mat::reshape() for the win.

and it's almost for free. only rows/cols get adjusted, no memory moved. i.e, mat = mat.reshape(1,1) would make a 1d float array of it.