def join_weights_and_biases(weights, biases):
    """
    joins two arrays into one
    :param weights: list of numpy arrays.
    :param biases: list of numpy arrays with same length as weights.
    :return: list of list with two numpy arrays for weights and biases, respectively.
        - the first index is defines layer and the second weight (0) or bias (1)
    """
    out = list()
    for i, _ in enumerate(weights):
        out.append([weights[i], biases[i]])
    return out