def _shape_array(array1, array2):
    """
    Function that equalises the input arrays by zero-padding the shortest one.

    ----------
    Parameters
    ----------
    array1: list or numpy.array
        Array
    array2: list or numpy.array
        Array

    Return
    ------
    arrays: numpy.array
        Array containing the equal-length arrays.
    """
    if len(array1) > len(array2):
        new_array = array2
        old_array = array1
    else:
        new_array = array1
        old_array = array2

    length = len(old_array) - len(new_array)

    for i in range(length):
        n = new_array[-1].copy()
        n[0::3] += 1
        n[2::3] = 0
        new_array = np.vstack([new_array, [n]])

    arrays = np.hstack([old_array, new_array])
    return arrays