Slice the underlying numpy array in sheet coordinates.

def select(cls, dataset, selection_mask=None, **selection):
        """
        Slice the underlying numpy array in sheet coordinates.
        """
        selection = {k: slice(*sel) if isinstance(sel, tuple) else sel
                     for k, sel in selection.items()}
        coords = tuple(selection[kd.name] if kd.name in selection else slice(None)
                       for kd in dataset.kdims)
        if not any([isinstance(el, slice) for el in coords]):
            return dataset.data[dataset.sheet2matrixidx(*coords)]

        # Apply slices
        xidx, yidx = coords
        l, b, r, t = dataset.bounds.lbrt()
        if isinstance(xidx, slice):
            l = l if xidx.start is None else max(l, xidx.start)
            r = r if xidx.stop is None else min(r, xidx.stop)
        if isinstance(yidx, slice):
            b = b if yidx.start is None else max(b, yidx.start)
            t = t if yidx.stop is None else min(t, yidx.stop)
        bounds = BoundingBox(points=((l, b), (r, t)))
        slc = Slice(bounds, dataset)
        return slc.submatrix(dataset.data)