def fillbackward(nds):
    for col in range(nds.shape[1]):
        for row in range(nds.shape[0] - 2, -1, -1):
            if math.isnan(nds[row, col]):
                nds[row, col] = nds[row+1, col]
@summary Removes NaNs from a 2D array by scanning backward in the 
dataset/ETHPy150Open QuantSoftware/QuantSoftwareToolkit/QSTK/qstkutil/tsutil.py/fillbackward