Trains and evaluate a simple MLP on the Reuters newswire topic classification task.

    from __future__ import print_function

    import numpy as np
    import keras
    from keras.datasets import reuters
    from keras.models import Sequential
    from keras.layers import Dense, Dropout, Activation
    from keras.preprocessing.text import Tokenizer

    max_words = 1000
    batch_size = 32
    epochs = 5

    print('Loading data...')
    (x_train, y_train), (x_test, y_test) = reuters.load_data(num_words=max_words,
                                                             test_split=0.2)
    print(len(x_train), 'train sequences')
    print(len(x_test), 'test sequences')

    num_classes = np.max(y_train) + 1
    print(num_classes, 'classes')

    print('Vectorizing sequence data...')
    tokenizer = Tokenizer(num_words=max_words)
    x_train = tokenizer.sequences_to_matrix(x_train, mode='binary')
    x_test = tokenizer.sequences_to_matrix(x_test, mode='binary')
    print('x_train shape:', x_train.shape)
    print('x_test shape:', x_test.shape)

    print('Convert class vector to binary class matrix '
          '(for use with categorical_crossentropy)')
    y_train = keras.utils.to_categorical(y_train, num_classes)
    y_test = keras.utils.to_categorical(y_test, num_classes)
    print('y_train shape:', y_train.shape)
    print('y_test shape:', y_test.shape)

    print('Building model...')
    model = Sequential()
    model.add(Dense(512, input_shape=(max_words,)))
    model.add(Activation('relu'))
    model.add(Dropout(0.5))
    model.add(Dense(num_classes))
    model.add(Activation('softmax'))

    model.compile(loss='categorical_crossentropy',
                  optimizer='adam',
                  metrics=['accuracy'])

    history = model.fit(x_train, y_train,
                        batch_size=batch_size,
                        epochs=epochs,
                        verbose=1,
                        validation_split=0.1)
    score = model.evaluate(x_test, y_test,
                           batch_size=batch_size, verbose=1)
    print('Test score:', score[0])
    print('Test accuracy:', score[1])

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