def string_from_array(arr):
    """Encode an array as a string code.

    Parameters
    ----------
    arr : (N, k) array_like
        *Numpy* array.

    Returns
    -------
    str
        String code of an array.

    Examples
    --------
    >>> string_from_array(np.array([1, 0, 0]))
    '100'
    >>> string_from_array(np.array([[1,0], [3,4]]))
    '1034'
    """
    return ''.join(map(str, arr.flat))