CNTK - Neural Network Classification


In this chapter, we will study how to classify neural network by using CNTK.

Introduction

Classification may be defined as the process to predict categorial output labels or responses for the given input data. The categorised output, which will be based on what the model has learned in training phase, can have the form such as "Black" or "White" or "spam" or "no spam".

On the other hand, mathematically, it is the task of approximating a mapping function say f from input variables say X to the output variables say Y.

A classic example of classification problem can be the spam detection in e-mails. It is obvious that there can be only two categories of output, "spam" and "no spam".

To implement such classification, we first need to do training of the classifier where "spam" and "no spam" emails would be used as the training data. Once, the classifier trained successfully, it can be used to detect an unknown email.

Here, we are going to create a 4-5-3 NN using iris flower dataset having the following −

Loading Dataset

We will be using iris flower dataset, from which we want to classify species of iris flowers based on the physical properties of sepal width and length, and petal width and length. The dataset describes the physical properties of different varieties of iris flowers −

We have iris.CSV file which we used before in previous chapters also. It can be loaded with the help of Pandas library. But, before using it or loading it for our classifier, we need to prepare the training and test files, so that it can be used easily with CNTK.

Preparing training & test files

Iris dataset is one of the most popular datasets for ML projects. It has 150 data items and the raw data looks as follows −

5.1 3.5 1.4 0.2 setosa
4.9 3.0 1.4 0.2 setosa
…
7.0 3.2 4.7 1.4 versicolor
6.4 3.2 4.5 1.5 versicolor
…
6.3 3.3 6.0 2.5 virginica
5.8 2.7 5.1 1.9 virginica

As told earlier, the first four values on each line describes the physical properties of different varieties, i.e. Sepal length, Sepal width, Petal length, Petal width of iris flowers.

But, we should have to convert the data in the format, that can be easily used by CNTK and that format is .ctf file (we created one iris.ctf in previous section also). It will look like as follows −

|attribs 5.1 3.5 1.4 0.2|species 1 0 0
|attribs 4.9 3.0 1.4 0.2|species 1 0 0
…
|attribs 7.0 3.2 4.7 1.4|species 0 1 0
|attribs 6.4 3.2 4.5 1.5|species 0 1 0
…
|attribs 6.3 3.3 6.0 2.5|species 0 0 1
|attribs 5.8 2.7 5.1 1.9|species 0 0 1

In the above data, the |attribs tag mark the start of the feature value and the |species tags the class label values. We can also use any other tag names of our wish, even we can add item ID as well. For example, look at the following data −

|ID 001 |attribs 5.1 3.5 1.4 0.2|species 1 0 0 |#setosa
|ID 002 |attribs 4.9 3.0 1.4 0.2|species 1 0 0 |#setosa
…
|ID 051 |attribs 7.0 3.2 4.7 1.4|species 0 1 0 |#versicolor
|ID 052 |attribs 6.4 3.2 4.5 1.5|species 0 1 0 |#versicolor
…

There are total 150 data items in iris dataset and for this example, we will be using 80-20 hold-out dataset rule i.e. 80% (120 items) data items for training purpose and remaining 20% (30 items) data items for testing purpose.

Constructing Classification model

First, we need to process the data files in CNTK format and for that we are going to use the helper function named create_reader as follows −

def create_reader(path, input_dim, output_dim, rnd_order, sweeps):
x_strm = C.io.StreamDef(field='attribs', shape=input_dim, is_sparse=False)
y_strm = C.io.StreamDef(field='species', shape=output_dim, is_sparse=False)
streams = C.io.StreamDefs(x_src=x_strm, y_src=y_strm)
deserial = C.io.CTFDeserializer(path, streams)
mb_src = C.io.MinibatchSource(deserial, randomize=rnd_order, max_sweeps=sweeps)
return mb_src

Now, we need to set the architecture arguments for our NN and also provide the location of the data files. It can be done with the help of following python code −

def main():
print("Using CNTK version = " + str(C.__version__) + "\n")
input_dim = 4
hidden_dim = 5
output_dim = 3
train_file = ".\\...\\" #provide the name of the training file(120 data items)
test_file = ".\\...\\" #provide the name of the test file(30 data items)

Now, with the help of following code line our program will create the untrained NN −

X = C.ops.input_variable(input_dim, np.float32)
Y = C.ops.input_variable(output_dim, np.float32)
with C.layers.default_options(init=C.initializer.uniform(scale=0.01, seed=1)):
hLayer = C.layers.Dense(hidden_dim, activation=C.ops.tanh, name='hidLayer')(X)
oLayer = C.layers.Dense(output_dim, activation=None, name='outLayer')(hLayer)
nnet = oLayer
model = C.ops.softmax(nnet)

Now, once we created the dual untrained model, we need to set up a Learner algorithm object and afterwards use it to create a Trainer training object. We are going to use SGD learner and cross_entropy_with_softmax loss function −

tr_loss = C.cross_entropy_with_softmax(nnet, Y)
tr_clas = C.classification_error(nnet, Y)
max_iter = 2000
batch_size = 10
learn_rate = 0.01
learner = C.sgd(nnet.parameters, learn_rate)
trainer = C.Trainer(nnet, (tr_loss, tr_clas), [learner])

Code the learning algorithm as follows −

max_iter = 2000
batch_size = 10
lr_schedule = C.learning_parameter_schedule_per_sample([(1000, 0.05), (1, 0.01)])
mom_sch = C.momentum_schedule([(100, 0.99), (0, 0.95)], batch_size)
learner = C.fsadagrad(nnet.parameters, lr=lr_schedule, momentum=mom_sch)
trainer = C.Trainer(nnet, (tr_loss, tr_clas), [learner])

Now, once we finished with Trainer object, we need to create a reader function to read the training data−

rdr = create_reader(train_file, input_dim, output_dim, rnd_order=True, sweeps=C.io.INFINITELY_REPEAT)
iris_input_map = { X : rdr.streams.x_src, Y : rdr.streams.y_src }

Now it’s time to train our NN model−

for i in range(0, max_iter):
curr_batch = rdr.next_minibatch(batch_size, input_map=iris_input_map) trainer.train_minibatch(curr_batch)
if i % 500 == 0:
mcee = trainer.previous_minibatch_loss_average
macc = (1.0 - trainer.previous_minibatch_evaluation_average) * 100
print("batch %4d: mean loss = %0.4f, accuracy = %0.2f%% " \ % (i, mcee, macc))

Once, we have done with training, let’s evaluate the model using test data items −

print("\nEvaluating test data \n")
rdr = create_reader(test_file, input_dim, output_dim, rnd_order=False, sweeps=1)
iris_input_map = { X : rdr.streams.x_src, Y : rdr.streams.y_src }
num_test = 30
all_test = rdr.next_minibatch(num_test, input_map=iris_input_map) acc = (1.0 - trainer.test_minibatch(all_test)) * 100
print("Classification accuracy = %0.2f%%" % acc)

After evaluating the accuracy of our trained NN model, we will be using it for making a prediction on unseen data −

np.set_printoptions(precision = 1, suppress=True)
unknown = np.array([[6.4, 3.2, 4.5, 1.5]], dtype=np.float32)
print("\nPredicting Iris species for input features: ")
print(unknown[0]) pred_prob = model.eval(unknown)
np.set_printoptions(precision = 4, suppress=True)
print("Prediction probabilities are: ")
print(pred_prob[0])

Complete Classification Model

Import numpy as np
Import cntk as C
def create_reader(path, input_dim, output_dim, rnd_order, sweeps):
x_strm = C.io.StreamDef(field='attribs', shape=input_dim, is_sparse=False)
y_strm = C.io.StreamDef(field='species', shape=output_dim, is_sparse=False)
streams = C.io.StreamDefs(x_src=x_strm, y_src=y_strm)
deserial = C.io.CTFDeserializer(path, streams)
mb_src = C.io.MinibatchSource(deserial, randomize=rnd_order, max_sweeps=sweeps)
return mb_src
def main():
print("Using CNTK version = " + str(C.__version__) + "\n")
input_dim = 4
hidden_dim = 5
output_dim = 3
train_file = ".\\...\\" #provide the name of the training file(120 data items)
test_file = ".\\...\\" #provide the name of the test file(30 data items)
X = C.ops.input_variable(input_dim, np.float32)
Y = C.ops.input_variable(output_dim, np.float32)
with C.layers.default_options(init=C.initializer.uniform(scale=0.01, seed=1)):
hLayer = C.layers.Dense(hidden_dim, activation=C.ops.tanh, name='hidLayer')(X)
oLayer = C.layers.Dense(output_dim, activation=None, name='outLayer')(hLayer)
nnet = oLayer
model = C.ops.softmax(nnet)
tr_loss = C.cross_entropy_with_softmax(nnet, Y)
tr_clas = C.classification_error(nnet, Y)
max_iter = 2000
batch_size = 10
learn_rate = 0.01
learner = C.sgd(nnet.parameters, learn_rate)
trainer = C.Trainer(nnet, (tr_loss, tr_clas), [learner])
max_iter = 2000
batch_size = 10
lr_schedule = C.learning_parameter_schedule_per_sample([(1000, 0.05), (1, 0.01)])
mom_sch = C.momentum_schedule([(100, 0.99), (0, 0.95)], batch_size)
learner = C.fsadagrad(nnet.parameters, lr=lr_schedule, momentum=mom_sch)
trainer = C.Trainer(nnet, (tr_loss, tr_clas), [learner])
rdr = create_reader(train_file, input_dim, output_dim, rnd_order=True, sweeps=C.io.INFINITELY_REPEAT)
iris_input_map = { X : rdr.streams.x_src, Y : rdr.streams.y_src }
for i in range(0, max_iter):
curr_batch = rdr.next_minibatch(batch_size, input_map=iris_input_map) trainer.train_minibatch(curr_batch)
if i % 500 == 0:
mcee = trainer.previous_minibatch_loss_average
macc = (1.0 - trainer.previous_minibatch_evaluation_average) * 100
print("batch %4d: mean loss = %0.4f, accuracy = %0.2f%% " \ % (i, mcee, macc))
print("\nEvaluating test data \n")
rdr = create_reader(test_file, input_dim, output_dim, rnd_order=False, sweeps=1)
iris_input_map = { X : rdr.streams.x_src, Y : rdr.streams.y_src }
num_test = 30
all_test = rdr.next_minibatch(num_test, input_map=iris_input_map) acc = (1.0 - trainer.test_minibatch(all_test)) * 100
print("Classification accuracy = %0.2f%%" % acc)
np.set_printoptions(precision = 1, suppress=True)
unknown = np.array([[7.0, 3.2, 4.7, 1.4]], dtype=np.float32)
print("\nPredicting species for input features: ")
print(unknown[0])
pred_prob = model.eval(unknown)
np.set_printoptions(precision = 4, suppress=True)
print("Prediction probabilities: ")
print(pred_prob[0])
if __name__== ”__main__”:
main()

Output

Using CNTK version = 2.7
batch 0: mean loss = 1.0986, mean accuracy = 40.00%
batch 500: mean loss = 0.6677, mean accuracy = 80.00%
batch 1000: mean loss = 0.5332, mean accuracy = 70.00%
batch 1500: mean loss = 0.2408, mean accuracy = 100.00%
Evaluating test data
Classification accuracy = 94.58%
Predicting species for input features:
[7.0 3.2 4.7 1.4]
Prediction probabilities:
[0.0847 0.736 0.113]

Saving the trained model

This Iris dataset has only 150 data items, hence it would take only a few seconds to train the NN classifier model, but training on a large dataset having hundred or thousand data items can take hours or even days.

We can save our model so that, we won’t have to retain it from scratch. With the help of following Python code, we can save our trained NN −

nn_classifier = “.\\neuralclassifier.model” #provide the name of the file
model.save(nn_classifier, format=C.ModelFormat.CNTKv2)

Following are the arguments of save() function used above −

Loading the trained model

Once you saved the trained model, it’s very easy to load that model. We only need to use the load () function. Let’s check this in the following example −

import numpy as np
import cntk as C
model = C.ops.functions.Function.load(“.\\neuralclassifier.model”)
np.set_printoptions(precision = 1, suppress=True)
unknown = np.array([[7.0, 3.2, 4.7, 1.4]], dtype=np.float32)
print("\nPredicting species for input features: ")
print(unknown[0])
pred_prob = model.eval(unknown)
np.set_printoptions(precision = 4, suppress=True)
print("Prediction probabilities: ")
print(pred_prob[0])

The benefit of saved model is that, once you load a saved model, it can be used exactly as if the model had just been trained.