plot_digits_dataset.py

# Taken from example in scikit-learn examples
# Authors: Fabian Pedregosa <fabian.pedregosa@inria.fr>
#          Olivier Grisel <olivier.grisel@ensta.org>
#          Mathieu Blondel <mathieu@mblondel.org>
#          Gael Varoquaux
# License: BSD 3 clause (C) INRIA 2011

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import offsetbox
from sklearn import datasets, decomposition


def digits_plot():
    digits = datasets.load_digits(n_class=6)
    n_digits = 500
    X = digits.data[:n_digits]
    y = digits.target[:n_digits]
    n_samples, n_features = X.shape

    def plot_embedding(X, title=None):
        x_min, x_max = np.min(X, 0), np.max(X, 0)
        X = (X - x_min) / (x_max - x_min)

        plt.figure()
        ax = plt.subplot(111)
        for i in range(X.shape[0]):
            plt.text(X[i, 0], X[i, 1], str(digits.target[i]),
                     color=plt.cm.Set1(y[i] / 10.),
                     fontdict={'weight': 'bold', 'size': 9})

        if hasattr(offsetbox, 'AnnotationBbox'):
            # only print thumbnails with matplotlib > 1.0
            shown_images = np.array([[1., 1.]])  # just something big
            for i in range(X.shape[0]):
                dist = np.sum((X[i] - shown_images) ** 2, 1)
                if np.min(dist) < 1e5:
                    # don't show points that are too close
                    # set a high threshold to basically turn this off
                    continue
                shown_images = np.r_[shown_images, [X[i]]]
                imagebox = offsetbox.AnnotationBbox(
                    offsetbox.OffsetImage(digits.images[i], cmap=plt.cm.gray_r),
                    X[i])
                ax.add_artist(imagebox)
        plt.xticks([]), plt.yticks([])
        if title is not None:
            plt.title(title)

    n_img_per_row = 10
    img = np.zeros((10 * n_img_per_row, 10 * n_img_per_row))
    for i in range(n_img_per_row):
        ix = 10 * i + 1
        for j in range(n_img_per_row):
            iy = 10 * j + 1
            img[ix:ix + 8, iy:iy + 8] = X[i * n_img_per_row + j].reshape((8, 8))

    plt.imshow(img, cmap=plt.cm.binary)
    plt.xticks([])
    plt.yticks([])
    plt.title('A selection from the 64-dimensional digits dataset')
    print("Computing PCA projection")
    pca = decomposition.PCA(n_components=2).fit(X)
    X_pca = pca.transform(X)
    plot_embedding(X_pca, "Principal Components projection of the digits")
    plt.figure()
    plt.title("First Principal Component")
    plt.matshow(pca.components_[0, :].reshape(8, 8), cmap="gray")
    plt.axis('off')
    plt.figure()
    plt.title("Second Principal Component")
    plt.matshow(pca.components_[1, :].reshape(8, 8), cmap="gray")
    plt.axis('off')
    plt.show()