def unshuffle(sinogram):
    """ unshuffle singram by angle

    Return a list of 51 sinograms, by unshuffling the provided
    sinogram; so that all projections in the result correspond
    to the same gantry rotation angle, analogous to a fluence map.

    Parameters
    ----------
    sinogram : np.array

    Returns
    -------
    unshuffled: list of sinograms

    """
    unshufd = [[] for i in range(51)]
    idx = 0
    for prj in sinogram:
        unshufd[idx].append(prj)
        idx = (idx + 1) % 51
    return unshufd
