text_fast.py

import tensorflow as tf
import numpy as np


class TextFast(object):
    """
    A FastText for text classification/regression.
    Uses an embedding layer, followed by a average, fully-connected (and softmax) layer.
    """
    def __init__(
      self, model_type, sequence_length, num_classes, vocab_size,
      embedding_size, l2_reg_lambda=0.0):

        # Placeholders for input, output and dropout
        self.input_x = tf.placeholder(tf.int32, [None, sequence_length], name="input_x")
        self.input_y = tf.placeholder(tf.float32, [None, num_classes], name="input_y")
        self.dropout_keep_prob = tf.placeholder(tf.float32, name="dropout_keep_prob")
        self.learning_rate = tf.placeholder(tf.float32, name="learning_rate")

        # Keeping track of l2 regularization loss (optional)
        l2_loss = tf.constant(0.0)

        # Embedding layer
        with tf.device('/cpu:0'), tf.name_scope("embedding"):
            # When trainable parameter equals True the embedding vector is non-static, otherwise is static
            self.W = tf.Variable(
                tf.random_uniform([vocab_size, embedding_size], -1.0, 1.0),
                name="W", trainable=True)
            self.embedded_chars = tf.nn.embedding_lookup(self.W, self.input_x) # [None, sequence_length, embedding_size]

        # Create a average layer (avg pooling)
        with tf.name_scope("avg-pool"):
            self.output = tf.reduce_mean(self.embedded_chars, axis=1)

        # Add dropout
        with tf.name_scope("dropout"):
            self.h_drop = tf.nn.dropout(self.output, self.dropout_keep_prob)

        # Final (unnormalized) scores and predictions
        with tf.name_scope("output"):
            W = tf.get_variable(
                "W",
                shape=[embedding_size, num_classes],
                initializer=tf.contrib.layers.xavier_initializer())
            b = tf.Variable(tf.constant(0.1, shape=[num_classes]), name="b")
            l2_loss += tf.nn.l2_loss(W)
            l2_loss += tf.nn.l2_loss(b)
            self.scores = tf.nn.xw_plus_b(self.h_drop, W, b, name="scores")
            if model_type == 'clf':
                self.predictions = tf.argmax(self.scores, 1, name="predictions")
            elif model_type == 'reg':
                self.predictions = tf.reduce_max(self.scores, 1, name="predictions")
                self.predictions = tf.expand_dims(self.predictions, -1)

        # Calculate mean cross-entropy loss, or root-mean-square error loss
        with tf.name_scope("loss"):
            if model_type == 'clf':
                losses = tf.nn.softmax_cross_entropy_with_logits(logits=self.scores, labels=self.input_y)
                self.loss = tf.reduce_mean(losses) + l2_reg_lambda * l2_loss
            elif model_type == 'reg':
                losses = tf.sqrt(tf.losses.mean_squared_error(predictions=self.predictions, labels=self.input_y))
                self.loss = tf.reduce_mean(losses) + l2_reg_lambda * l2_loss

        # Accuracy
        with tf.name_scope("accuracy"):
            if model_type == 'clf':
                correct_predictions = tf.equal(self.predictions, tf.argmax(self.input_y, 1))
                self.accuracy = tf.reduce_mean(tf.cast(correct_predictions, "float"), name="accuracy")
            elif model_type == 'reg':
                self.accuracy = tf.constant(0.0, name="accuracy")