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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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# See the License for the specific language governing permissions and
# limitations under the License.
Objetivos de aprendizaje:
Nuestro objetivo es asignar cada imagen de entrada al dígito numérico correcto. Crearemos una red neural con algunas capas ocultas y una capa de softmax en la parte superior para seleccionar la clase ganadora.
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from __future__ import print_function
import glob
import math
import os
from IPython import display
from matplotlib import cm
from matplotlib import gridspec
from matplotlib import pyplot as plt
import numpy as np
import pandas as pd
import seaborn as sns
from sklearn import metrics
import tensorflow as tf
from tensorflow.python.data import Dataset
tf.logging.set_verbosity(tf.logging.ERROR)
pd.options.display.max_rows = 10
pd.options.display.float_format = '{:.1f}'.format
mnist_dataframe = pd.read_csv(
"https://download.mlcc.google.com/mledu-datasets/mnist_train_small.csv",
sep=",",
header=None)
# Use just the first 10,000 records for training/validation.
mnist_dataframe = mnist_dataframe.head(10000)
mnist_dataframe = mnist_dataframe.reindex(np.random.permutation(mnist_dataframe.index))
mnist_dataframe.head()
La primera columna contiene la etiqueta de clase. Las columnas restantes contienen los valores de los atributos, uno por píxel para los valores de píxel de 28×28=784. La mayoría de estos valores de píxel de 784 son cero; es posible que quieras dedicar un minuto a confirmar que no sean todos cero.
Estos ejemplos son imágenes de números escritos a mano con una resolución relativamente baja y alto contraste. Se representa cada uno de los diez dígitos de 0-9, con una etiqueta de clase única para cada dígito posible. Por lo tanto, este es un problema de clasificación de clase múltiple con 10 clases.
Ahora, analicemos las etiquetas y atributos, y observemos algunos ejemplos. Observa el uso de loc, que nos permite extraer columnas en función de la ubicación original, ya que no tenemos una fila de encabezado en este conjunto de datos.
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def parse_labels_and_features(dataset):
"""Extracts labels and features.
This is a good place to scale or transform the features if needed.
Args:
dataset: A Pandas `Dataframe`, containing the label on the first column and
monochrome pixel values on the remaining columns, in row major order.
Returns:
A `tuple` `(labels, features)`:
labels: A Pandas `Series`.
features: A Pandas `DataFrame`.
"""
labels = dataset[0]
# DataFrame.loc index ranges are inclusive at both ends.
features = dataset.loc[:,1:784]
# Scale the data to [0, 1] by dividing out the max value, 255.
features = features / 255
return labels, features
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training_targets, training_examples = parse_labels_and_features(mnist_dataframe[:7500])
training_examples.describe()
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validation_targets, validation_examples = parse_labels_and_features(mnist_dataframe[7500:10000])
validation_examples.describe()
Muestra un ejemplo al azar y su etiqueta correspondiente.
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rand_example = np.random.choice(training_examples.index)
_, ax = plt.subplots()
ax.matshow(training_examples.loc[rand_example].values.reshape(28, 28))
ax.set_title("Label: %i" % training_targets.loc[rand_example])
ax.grid(False)
Primero, creemos un modelo de punto de referencia que sirva como comparación. El LinearClassifier proporciona un conjunto de clasificadores k de uno frente a todos, uno para cada clase k.
Observarás que, además de informar la exactitud y representar la pérdida logística en el tiempo, también mostramos una matriz de confusión. La matriz de confusión muestra qué clases se clasificaron de forma incorrecta como otras clases. ¿Qué dígitos se confundieron con otros?
Observa también que el error del modelo se rastrea a través de la función de log_loss. Esta no debe confundirse con la función de pérdida interna de LinearClassifier que se usó para el entrenamiento.
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def construct_feature_columns():
"""Construct the TensorFlow Feature Columns.
Returns:
A set of feature columns
"""
# There are 784 pixels in each image.
return set([tf.feature_column.numeric_column('pixels', shape=784)])
Aquí, haremos funciones de entrada independientes para el entrenamiento y la predicción. Las anidaremos en create_training_input_fn() y create_predict_input_fn(), respectivamente, para poder invocarlas para devolver las funciones _input_fn correspondientes para pasar nuestras llamadas de .train() y .predict().
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def create_training_input_fn(features, labels, batch_size, num_epochs=None, shuffle=True):
"""A custom input_fn for sending MNIST data to the estimator for training.
Args:
features: The training features.
labels: The training labels.
batch_size: Batch size to use during training.
Returns:
A function that returns batches of training features and labels during
training.
"""
def _input_fn(num_epochs=None, shuffle=True):
# Input pipelines are reset with each call to .train(). To ensure model
# gets a good sampling of data, even when number of steps is small, we
# shuffle all the data before creating the Dataset object
idx = np.random.permutation(features.index)
raw_features = {"pixels":features.reindex(idx)}
raw_targets = np.array(labels[idx])
ds = Dataset.from_tensor_slices((raw_features,raw_targets)) # warning: 2GB limit
ds = ds.batch(batch_size).repeat(num_epochs)
if shuffle:
ds = ds.shuffle(10000)
# Return the next batch of data.
feature_batch, label_batch = ds.make_one_shot_iterator().get_next()
return feature_batch, label_batch
return _input_fn
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def create_predict_input_fn(features, labels, batch_size):
"""A custom input_fn for sending mnist data to the estimator for predictions.
Args:
features: The features to base predictions on.
labels: The labels of the prediction examples.
Returns:
A function that returns features and labels for predictions.
"""
def _input_fn():
raw_features = {"pixels": features.values}
raw_targets = np.array(labels)
ds = Dataset.from_tensor_slices((raw_features, raw_targets)) # warning: 2GB limit
ds = ds.batch(batch_size)
# Return the next batch of data.
feature_batch, label_batch = ds.make_one_shot_iterator().get_next()
return feature_batch, label_batch
return _input_fn
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def train_linear_classification_model(
learning_rate,
steps,
batch_size,
training_examples,
training_targets,
validation_examples,
validation_targets):
"""Trains a linear classification model for the MNIST digits dataset.
In addition to training, this function also prints training progress information,
a plot of the training and validation loss over time, and a confusion
matrix.
Args:
learning_rate: A `float`, the learning rate to use.
steps: A non-zero `int`, the total number of training steps. A training step
consists of a forward and backward pass using a single batch.
batch_size: A non-zero `int`, the batch size.
training_examples: A `DataFrame` containing the training features.
training_targets: A `DataFrame` containing the training labels.
validation_examples: A `DataFrame` containing the validation features.
validation_targets: A `DataFrame` containing the validation labels.
Returns:
The trained `LinearClassifier` object.
"""
periods = 10
steps_per_period = steps / periods
# Create the input functions.
predict_training_input_fn = create_predict_input_fn(
training_examples, training_targets, batch_size)
predict_validation_input_fn = create_predict_input_fn(
validation_examples, validation_targets, batch_size)
training_input_fn = create_training_input_fn(
training_examples, training_targets, batch_size)
# Create a LinearClassifier object.
my_optimizer = tf.train.AdagradOptimizer(learning_rate=learning_rate)
my_optimizer = tf.contrib.estimator.clip_gradients_by_norm(my_optimizer, 5.0)
classifier = tf.estimator.LinearClassifier(
feature_columns=construct_feature_columns(),
n_classes=10,
optimizer=my_optimizer,
config=tf.estimator.RunConfig(keep_checkpoint_max=1)
)
# Train the model, but do so inside a loop so that we can periodically assess
# loss metrics.
print("Training model...")
print("LogLoss error (on validation data):")
training_errors = []
validation_errors = []
for period in range (0, periods):
# Train the model, starting from the prior state.
classifier.train(
input_fn=training_input_fn,
steps=steps_per_period
)
# Take a break and compute probabilities.
training_predictions = list(classifier.predict(input_fn=predict_training_input_fn))
training_probabilities = np.array([item['probabilities'] for item in training_predictions])
training_pred_class_id = np.array([item['class_ids'][0] for item in training_predictions])
training_pred_one_hot = tf.keras.utils.to_categorical(training_pred_class_id,10)
validation_predictions = list(classifier.predict(input_fn=predict_validation_input_fn))
validation_probabilities = np.array([item['probabilities'] for item in validation_predictions])
validation_pred_class_id = np.array([item['class_ids'][0] for item in validation_predictions])
validation_pred_one_hot = tf.keras.utils.to_categorical(validation_pred_class_id,10)
# Compute training and validation errors.
training_log_loss = metrics.log_loss(training_targets, training_pred_one_hot)
validation_log_loss = metrics.log_loss(validation_targets, validation_pred_one_hot)
# Occasionally print the current loss.
print(" period %02d : %0.2f" % (period, validation_log_loss))
# Add the loss metrics from this period to our list.
training_errors.append(training_log_loss)
validation_errors.append(validation_log_loss)
print("Model training finished.")
# Remove event files to save disk space.
_ = map(os.remove, glob.glob(os.path.join(classifier.model_dir, 'events.out.tfevents*')))
# Calculate final predictions (not probabilities, as above).
final_predictions = classifier.predict(input_fn=predict_validation_input_fn)
final_predictions = np.array([item['class_ids'][0] for item in final_predictions])
accuracy = metrics.accuracy_score(validation_targets, final_predictions)
print("Final accuracy (on validation data): %0.2f" % accuracy)
# Output a graph of loss metrics over periods.
plt.ylabel("LogLoss")
plt.xlabel("Periods")
plt.title("LogLoss vs. Periods")
plt.plot(training_errors, label="training")
plt.plot(validation_errors, label="validation")
plt.legend()
plt.show()
# Output a plot of the confusion matrix.
cm = metrics.confusion_matrix(validation_targets, final_predictions)
# Normalize the confusion matrix by row (i.e by the number of samples
# in each class).
cm_normalized = cm.astype("float") / cm.sum(axis=1)[:, np.newaxis]
ax = sns.heatmap(cm_normalized, cmap="bone_r")
ax.set_aspect(1)
plt.title("Confusion matrix")
plt.ylabel("True label")
plt.xlabel("Predicted label")
plt.show()
return classifier
Dedica 5 minutos a observar qué nivel de eficacia tienes con respecto a la exactitud en un modelo lineal de esta forma. Para este ejercicio, limítate a experimentar con los hiperparámetros para el tamaño del lote, la tasa de aprendizaje y los pasos.
Detente si obtienes algún resultado de una exactitud por encima de 0.9 aproximadamente.
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classifier = train_linear_classification_model(
learning_rate=0.02,
steps=100,
batch_size=10,
training_examples=training_examples,
training_targets=training_targets,
validation_examples=validation_examples,
validation_targets=validation_targets)
Aquí se incluye un conjunto de parámetros que debería dar una exactitud de aproximadamente 0.9.
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_ = train_linear_classification_model(
learning_rate=0.03,
steps=1000,
batch_size=30,
training_examples=training_examples,
training_targets=training_targets,
validation_examples=validation_examples,
validation_targets=validation_targets)
Reemplaza el LinearClassifier anterior por un DNNClassifier y busca una combinación de parámetros que dé una exactitud de 0.95 o mejor.
Es posible que quieras experimentar con otros métodos de regularización, como de retirados. Estos métodos de regularización adicionales están documentados en los comentarios de la clase DNNClassifier.
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#
# YOUR CODE HERE: Replace the linear classifier with a neural network.
#
Una vez que tengas un buen modelo, comprueba no haber sobreajustado el conjunto de validación al evaluar los datos de prueba que cargaremos más abajo.
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mnist_test_dataframe = pd.read_csv(
"https://download.mlcc.google.com/mledu-datasets/mnist_test.csv",
sep=",",
header=None)
test_targets, test_examples = parse_labels_and_features(mnist_test_dataframe)
test_examples.describe()
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#
# YOUR CODE HERE: Calculate accuracy on the test set.
#
El código que aparece más abajo es casi idéntico al código de entrenamiento de LinearClassifer original, a excepción de la configuración específica de la red neural, como el hiperparámetro para unidades ocultas.
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def train_nn_classification_model(
learning_rate,
steps,
batch_size,
hidden_units,
training_examples,
training_targets,
validation_examples,
validation_targets):
"""Trains a neural network classification model for the MNIST digits dataset.
In addition to training, this function also prints training progress information,
a plot of the training and validation loss over time, as well as a confusion
matrix.
Args:
learning_rate: A `float`, the learning rate to use.
steps: A non-zero `int`, the total number of training steps. A training step
consists of a forward and backward pass using a single batch.
batch_size: A non-zero `int`, the batch size.
hidden_units: A `list` of int values, specifying the number of neurons in each layer.
training_examples: A `DataFrame` containing the training features.
training_targets: A `DataFrame` containing the training labels.
validation_examples: A `DataFrame` containing the validation features.
validation_targets: A `DataFrame` containing the validation labels.
Returns:
The trained `DNNClassifier` object.
"""
periods = 10
# Caution: input pipelines are reset with each call to train.
# If the number of steps is small, your model may never see most of the data.
# So with multiple `.train` calls like this you may want to control the length
# of training with num_epochs passed to the input_fn. Or, you can do a really-big shuffle,
# or since it's in-memory data, shuffle all the data in the `input_fn`.
steps_per_period = steps / periods
# Create the input functions.
predict_training_input_fn = create_predict_input_fn(
training_examples, training_targets, batch_size)
predict_validation_input_fn = create_predict_input_fn(
validation_examples, validation_targets, batch_size)
training_input_fn = create_training_input_fn(
training_examples, training_targets, batch_size)
# Create the input functions.
predict_training_input_fn = create_predict_input_fn(
training_examples, training_targets, batch_size)
predict_validation_input_fn = create_predict_input_fn(
validation_examples, validation_targets, batch_size)
training_input_fn = create_training_input_fn(
training_examples, training_targets, batch_size)
# Create feature columns.
feature_columns = [tf.feature_column.numeric_column('pixels', shape=784)]
# Create a DNNClassifier object.
my_optimizer = tf.train.AdagradOptimizer(learning_rate=learning_rate)
my_optimizer = tf.contrib.estimator.clip_gradients_by_norm(my_optimizer, 5.0)
classifier = tf.estimator.DNNClassifier(
feature_columns=feature_columns,
n_classes=10,
hidden_units=hidden_units,
optimizer=my_optimizer,
config=tf.contrib.learn.RunConfig(keep_checkpoint_max=1)
)
# Train the model, but do so inside a loop so that we can periodically assess
# loss metrics.
print("Training model...")
print("LogLoss error (on validation data):")
training_errors = []
validation_errors = []
for period in range (0, periods):
# Train the model, starting from the prior state.
classifier.train(
input_fn=training_input_fn,
steps=steps_per_period
)
# Take a break and compute probabilities.
training_predictions = list(classifier.predict(input_fn=predict_training_input_fn))
training_probabilities = np.array([item['probabilities'] for item in training_predictions])
training_pred_class_id = np.array([item['class_ids'][0] for item in training_predictions])
training_pred_one_hot = tf.keras.utils.to_categorical(training_pred_class_id,10)
validation_predictions = list(classifier.predict(input_fn=predict_validation_input_fn))
validation_probabilities = np.array([item['probabilities'] for item in validation_predictions])
validation_pred_class_id = np.array([item['class_ids'][0] for item in validation_predictions])
validation_pred_one_hot = tf.keras.utils.to_categorical(validation_pred_class_id,10)
# Compute training and validation errors.
training_log_loss = metrics.log_loss(training_targets, training_pred_one_hot)
validation_log_loss = metrics.log_loss(validation_targets, validation_pred_one_hot)
# Occasionally print the current loss.
print(" period %02d : %0.2f" % (period, validation_log_loss))
# Add the loss metrics from this period to our list.
training_errors.append(training_log_loss)
validation_errors.append(validation_log_loss)
print("Model training finished.")
# Remove event files to save disk space.
_ = map(os.remove, glob.glob(os.path.join(classifier.model_dir, 'events.out.tfevents*')))
# Calculate final predictions (not probabilities, as above).
final_predictions = classifier.predict(input_fn=predict_validation_input_fn)
final_predictions = np.array([item['class_ids'][0] for item in final_predictions])
accuracy = metrics.accuracy_score(validation_targets, final_predictions)
print("Final accuracy (on validation data): %0.2f" % accuracy)
# Output a graph of loss metrics over periods.
plt.ylabel("LogLoss")
plt.xlabel("Periods")
plt.title("LogLoss vs. Periods")
plt.plot(training_errors, label="training")
plt.plot(validation_errors, label="validation")
plt.legend()
plt.show()
# Output a plot of the confusion matrix.
cm = metrics.confusion_matrix(validation_targets, final_predictions)
# Normalize the confusion matrix by row (i.e by the number of samples
# in each class).
cm_normalized = cm.astype("float") / cm.sum(axis=1)[:, np.newaxis]
ax = sns.heatmap(cm_normalized, cmap="bone_r")
ax.set_aspect(1)
plt.title("Confusion matrix")
plt.ylabel("True label")
plt.xlabel("Predicted label")
plt.show()
return classifier
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classifier = train_nn_classification_model(
learning_rate=0.05,
steps=1000,
batch_size=30,
hidden_units=[100, 100],
training_examples=training_examples,
training_targets=training_targets,
validation_examples=validation_examples,
validation_targets=validation_targets)
A continuación, verificaremos la exactitud del conjunto de prueba.
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mnist_test_dataframe = pd.read_csv(
"https://download.mlcc.google.com/mledu-datasets/mnist_test.csv",
sep=",",
header=None)
test_targets, test_examples = parse_labels_and_features(mnist_test_dataframe)
test_examples.describe()
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predict_test_input_fn = create_predict_input_fn(
test_examples, test_targets, batch_size=100)
test_predictions = classifier.predict(input_fn=predict_test_input_fn)
test_predictions = np.array([item['class_ids'][0] for item in test_predictions])
accuracy = metrics.accuracy_score(test_targets, test_predictions)
print("Accuracy on test data: %0.2f" % accuracy)
Dediquemos unos minutos a examinar nuestra red neural y observar qué aprendió al acceder al atributo weights_ de nuestro modelo.
La capa de entrada de nuestro modelo tiene 784 ponderaciones correspondientes a las imágenes de entrada de 28×28 píxeles. La primera capa oculta tendrá 784×N ponderaciones, donde N es el número de nodos en esa capa. Podemos regresar esas ponderaciones a imágenes de 28×28 al cambiar la forma de cada una de las matrices N de 1×784 de las ponderaciones a matrices N de un tamaño de 28×28.
Ejecuta la siguiente celda para representar las ponderaciones. Ten en cuenta que esta celda requiere que ya se haya entrenado un DNNClassifier denominado "clasificador".
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print(classifier.get_variable_names())
weights0 = classifier.get_variable_value("dnn/hiddenlayer_0/kernel")
print("weights0 shape:", weights0.shape)
num_nodes = weights0.shape[1]
num_rows = int(math.ceil(num_nodes / 10.0))
fig, axes = plt.subplots(num_rows, 10, figsize=(20, 2 * num_rows))
for coef, ax in zip(weights0.T, axes.ravel()):
# Weights in coef is reshaped from 1x784 to 28x28.
ax.matshow(coef.reshape(28, 28), cmap=plt.cm.pink)
ax.set_xticks(())
ax.set_yticks(())
plt.show()
La primera capa oculta de la red neural debe modelar atributos de un nivel bastante bajo, de manera que la visualización de las ponderaciones probablemente mostrará algunas manchas borrosas o, posiblemente, partes de dígitos. Es posible que también veas algunas neuronas que básicamente sean inconsistencias; estas no tienen convergencia o se ignoran por parte de las capas más altas.
Puede resultar interesante detener el entrenamiento en diferentes números de iteraciones y observar el efecto.
Entrena el clasificador para 10, 100 y 1,000 pasos, respectivamente. A continuación, vuelve a ejecutar esta visualización.
¿Qué diferencias observas visualmente para los diferentes niveles de convergencia?