def create_dim(a, dim=''):
    """create dimension array for n-nested array
    example:
    >>> create_dim([[1,2],[3,4],[5,6,[7,8],]])
    [['0-0', '0-1'], ['1-0', '1-1'], ['2-0', '2-1', ['2-2-0', '2-2-1']]]
    >>> create_dim(5)
    ''
    >>> create_dim([5,5])
    ['0', '1']
    """
    if isinstance(a, list):
        if dim:
            prefix = dim + '-'
        else:
            prefix = ''
        return([create_dim(a_, prefix + str(i)) for i, a_ in enumerate(a)])
    else:
        return(dim)