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Tensorflow: Kaggle Spooky Authors Bag of Words Model

I've been playing around with some Tensorflow tutorials recently and wanted to see if I could create a submission for Kaggle's Spooky Author Identification competition that I've written about recently.

My model is based on one from the text classification tutorial. The tutorial shows how to create custom Estimators which we can learn more about in a post on the Google Developers blog.

Imports

Let's get started. First, our imports:


from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import numpy as np
import pandas as pd
import tensorflow as tf
from sklearn import preprocessing
from sklearn.model_selection import train_test_split

We've obviously got Tensorflow, but also scikit-learn which we'll use to split our data into a training and test sets as well as convert the author names into numeric values.

Model building functions

Next we'll create a function to create a bag of words model. This function calls another one that creates different EstimatorSpecs depending on the context it's called from.


EMBEDDING_SIZE = 50
MAX_LABEL = 3
WORDS_FEATURE = 'words'  # Name of the input words feature.


def bag_of_words_model(features, labels, mode):
    bow_column = tf.feature_column.categorical_column_with_identity(WORDS_FEATURE, num_buckets=n_words)
    bow_embedding_column = tf.feature_column.embedding_column(bow_column, dimension=EMBEDDING_SIZE)
    bow = tf.feature_column.input_layer(features, feature_columns=[bow_embedding_column])
    logits = tf.layers.dense(bow, MAX_LABEL, activation=None)
    return create_estimator_spec(logits=logits, labels=labels, mode=mode)


def create_estimator_spec(logits, labels, mode):
    predicted_classes = tf.argmax(logits, 1)
    if mode == tf.estimator.ModeKeys.PREDICT:
        return tf.estimator.EstimatorSpec(
            mode=mode,
            predictions={
                'class': predicted_classes,
                'prob': tf.nn.softmax(logits),
                'log_loss': tf.nn.softmax(logits),
            })

    loss = tf.losses.sparse_softmax_cross_entropy(labels=labels, logits=logits)
    if mode == tf.estimator.ModeKeys.TRAIN:
        optimizer = tf.train.AdamOptimizer(learning_rate=0.01)
        train_op = optimizer.minimize(loss, global_step=tf.train.get_global_step())
        return tf.estimator.EstimatorSpec(mode, loss=loss, train_op=train_op)

    eval_metric_ops = {
        'accuracy': tf.metrics.accuracy(labels=labels, predictions=predicted_classes)
    }
    return tf.estimator.EstimatorSpec(mode=mode, loss=loss, eval_metric_ops=eval_metric_ops)

Loading data

Now we're ready to load our data.


Y_COLUMN = "author"
TEXT_COLUMN = "text"
le = preprocessing.LabelEncoder()

train_df = pd.read_csv("train.csv")
X = pd.Series(train_df[TEXT_COLUMN])
y = le.fit_transform(train_df[Y_COLUMN].copy())
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.33, random_state=42)

The only interesting thing here is the LabelEncoder. We'll keep that around as we'll use it later as well.

Transform documents

At the moment our training and test dataframes contain text, but Tensorflow works with vectors so we need to convert our data into that format. We can use the VocabularyProcessor to do this:


MAX_DOCUMENT_LENGTH = 100
vocab_processor = tf.contrib.learn.preprocessing.VocabularyProcessor(MAX_DOCUMENT_LENGTH)

X_transform_train = vocab_processor.fit_transform(X_train)
X_transform_test = vocab_processor.transform(X_test)

X_train = np.array(list(X_transform_train))
X_test = np.array(list(X_transform_test))

n_words = len(vocab_processor.vocabulary_)
print('Total words: %d' % n_words)

Training our model

Finally we're ready to train our model! We'll call the Bag of Words model we created at the beginning and build a train input function where we pass in the training arrays that we just created:


model_fn = bag_of_words_model
classifier = tf.estimator.Estimator(model_fn=model_fn)

train_input_fn = tf.estimator.inputs.numpy_input_fn(
    x={WORDS_FEATURE: X_train},
    y=y_train,
    batch_size=len(X_train),
    num_epochs=None,
    shuffle=True)
classifier.train(input_fn=train_input_fn, steps=100)

Evaluating our model

Let's see how our model fares. We'll call the evaluate function with our test data:


test_input_fn = tf.estimator.inputs.numpy_input_fn(
    x={WORDS_FEATURE: X_test},
    y=y_test,
    num_epochs=1,
    shuffle=False)

scores = classifier.evaluate(input_fn=test_input_fn)
print('Accuracy: {0:f}, Loss {1:f}'.format(scores['accuracy'], scores["loss"]))

INFO:tensorflow:Saving checkpoints for 1 into /var/folders/k5/ssmkw9vd2yb3h5wnqlxnqbkw0000gn/T/tmpb6v4rrrn/model.ckpt.
INFO:tensorflow:loss = 1.0888131, step = 1
INFO:tensorflow:Saving checkpoints for 100 into /var/folders/k5/ssmkw9vd2yb3h5wnqlxnqbkw0000gn/T/tmpb6v4rrrn/model.ckpt.
INFO:tensorflow:Loss for final step: 0.18394235.
INFO:tensorflow:Starting evaluation at 2018-01-28-22:41:34
INFO:tensorflow:Restoring parameters from /var/folders/k5/ssmkw9vd2yb3h5wnqlxnqbkw0000gn/T/tmpb6v4rrrn/model.ckpt-100
INFO:tensorflow:Finished evaluation at 2018-01-28-22:41:34
INFO:tensorflow:Saving dict for global step 100: accuracy = 0.8246673, global_step = 100, loss = 0.44942895
Accuracy: 0.824667, Loss 0.449429

Not too bad! I managed to get a log loss score of ~ 0.36 with a scikit-learn ensemble model but it is better than some of my first attempts.

Generating predictions

I wanted to see how it'd do against Kaggle's test dataset so I generated a CSV file with predictions:


test_df = pd.read_csv("test.csv")

X_test = pd.Series(test_df[TEXT_COLUMN])
X_test = np.array(list(vocab_processor.transform(X_test)))

test_input_fn = tf.estimator.inputs.numpy_input_fn(
    x={WORDS_FEATURE: X_test},
    num_epochs=1,
    shuffle=False)

predictions = classifier.predict(test_input_fn)
y_predicted_classes = np.array(list(p['prob'] for p in predictions))

output = pd.DataFrame(y_predicted_classes, columns=le.classes_)
output["id"] = test_df["id"]
output.to_csv("output.csv", index=False, float_format='%.6f')

Here we go:

2018 01 29 06 44 30

The score is roughly the same as we saw with the test split of the training set. If you want to see all the code in one place I've put it on my Spooky Authors GitHub repository.

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