def plot_two_digit_freqs(f2):
    """
    Plot two digits frequency counts using matplotlib.
    """
    f2_copy = f2.copy()
    f2_copy.shape = (10,10)
    ax = plt.matshow(f2_copy)
    plt.colorbar()
    for i in range(10):
        for j in range(10):
            plt.text(i-0.2, j+0.2, str(j)+str(i))
    plt.ylabel('First digit')
    plt.xlabel('Second digit')
    return ax
Plot two digits frequency counts using matplotlib.