/* Load libraries */ import numpy as np from keras.datasets import imdb from keras.preprocessing.text import Tokenizer from keras import models from keras import layers /* Set random seed */ np.random.seed(0)
Using TensorFlow backend.
Load Movie Review Data
/* Set the number of features we want */ number_of_features = 1000 /* Load data and target vector from movie review data */ (train_data, train_target), (test_data, test_target) = imdb.load_data(num_words=number_of_features) /* Convert movie review data to one-hot encoded feature matrix */ tokenizer = Tokenizer(num_words=number_of_features) train_features = tokenizer.sequences_to_matrix(train_data, mode='binary') test_features = tokenizer.sequences_to_matrix(test_data, mode='binary')
Construct Neural Network Architecture
Because this is a binary classification problem, one common choice is to use the sigmoid activation function in a one-unit output layer.
/* Start neural network */ network = models.Sequential() /* Add fully connected layer with a ReLU activation function */ network.add(layers.Dense(units=16, activation='relu', input_shape=(number_of_features,))) /* Add fully connected layer with a ReLU activation function */ network.add(layers.Dense(units=16, activation='relu')) /* Add fully connected layer with a sigmoid activation function */ network.add(layers.Dense(units=1, activation='sigmoid'))
Compile Feedforward Neural Network
/* Compile neural network */ network.compile(loss='binary_crossentropy', # Cross-entropy optimizer='rmsprop', # Root Mean Square Propagation metrics=['accuracy']) # Accuracy performance metric
Train Feedforward Neural Network
In Keras, we train our neural network using the
fit method. There are six significant parameters to define. The first two parameters are the features and target vector of the training data.
epochs parameter defines how many epochs to use when training the data.
verbose determines how much information is outputted during the training process, with
0 being no out,
1 outputting a progress bar, and
2 one log line per epoch.
batch_size sets the number of observations to propagate through the network before updating the parameters.
Finally, we held out a test set of data to use to evaluate the model. These test features and test target vector can be arguments of the
validation_data, which will use them for evaluation. Alternatively, we could have used
validation_split to define what fraction of the training data we want to hold out for evaluation.
fit method returned a trained model, however in Keras the
fit method returns a
History object containing the loss values and performance metrics at each epoch.
/* Train neural network */ history = network.fit(train_features, # Features train_target, # Target vector epochs=3, # Number of epochs verbose=1, # Print description after each epoch batch_size=100, # Number of observations per batch validation_data=(test_features, test_target)) # Data for evaluation
Train on 25000 samples, validate on 25000 samples Epoch 1/3 25000/25000 [==============================] - 2s - loss: 0.4215 - acc: 0.8102 - val_loss: 0.3385 - val_acc: 0.8558 Epoch 2/3 25000/25000 [==============================] - 1s - loss: 0.3241 - acc: 0.8646 - val_loss: 0.3261 - val_acc: 0.8626 Epoch 3/3 25000/25000 [==============================] - 2s - loss: 0.3120 - acc: 0.8700 - val_loss: 0.3268 - val_acc: 0.8593